NBME Clinical Science Subject Examination (Shelf Exam) — Questions and Answers

Question 1: A 16-year-old boy is undergoing evaluation for jaundice. Laboratory studies show normal hepatic enzyme activities, a negative direct antiglobulin (Coombs) test, increased mean corpuscular hemoglobin concentration, and increased osmotic fragility of erythrocytes. Which of the following types of erythrocyte is most likely to be seen on a peripheral blood smear?

Spherocyte (Correct answer)
Schistocyte
Target cell
Teardrop cell
Ovalocyte

Correct answer: Spherocyte

The combination of jaundice, normal hepatic enzymes, negative Coombs test, increased mean corpuscular hemoglobin concentration (MCHC), and increased osmotic fragility is highly characteristic of hereditary spherocytosis. This genetic disorder causes red blood cells to be spherical, rigid, and more fragile, leading to their premature destruction in the spleen. Spherocytes are the hallmark finding on a peripheral blood smear in this condition.

Question 2: A 32-year-old heroin user presents to the ED in acute opioid withdrawal with severe anxiety, mydriasis, piloerection, and cramping. Which agent reduces autonomic symptoms of opioid withdrawal?

Naloxone
Clonidine (Correct answer)
Buprenorphine
Methadone

Correct answer: Clonidine

Clonidine, an alpha-2 agonist, suppresses the noradrenergic storm driving autonomic symptoms of opioid withdrawal.

Question 3: A previously healthy 39-year-old woman is brought to the physician because of a tingling sensation in her fingers and toes for 2 days and rapidly progressive weakness of her legs. She had an upper respiratory tract infection 2 weeks ago. She was unable to get up from bed this morning. Examination shows weakness of all four extremities, distal greater than proximal. Deep tendon reflexes are absent. Sensation is mildly decreased over the feet. Which of the following is the most likely diagnosis?

Myasthenia gravis
Guillain-Barré syndrome (Correct answer)
Multiple sclerosis
Poliomyelitis
Tick paralysis

Correct answer: Guillain-Barré syndrome

This patient's presentation of rapidly progressive, ascending weakness (legs first, then all four extremities, distal greater than proximal), accompanied by tingling sensations and absent deep tendon reflexes, is highly characteristic of Guillain-Barré syndrome (GBS). The preceding upper respiratory tract infection 2 weeks prior is a common trigger for this acute demyelinating polyneuropathy, where the immune system attacks peripheral nerves.

Question 4: A 2-year-old boy is diagnosed with staphylococcal scalded skin syndrome. In vitro studies show the causal organism to be resistant to penicillin. Which of the following mechanisms of action is most likely involved in this resistance?

Mutation of the 50S ribosomal subunit
Active efflux of the antibiotic from the bacteria
Mutation of the 30S ribosomal subunit
Production of β-lactamase by the bacteria (Correct answer)
Decreased uptake of the antibiotic into the bacteria

Correct answer: Production of β-lactamase by the bacteria

Staphylococcus aureus is a common cause of staphylococcal scalded skin syndrome. The most prevalent mechanism of penicillin resistance in S. aureus is the production of β-lactamase (penicillinase). This enzyme hydrolyzes the β-lactam ring of penicillin, rendering the antibiotic inactive and preventing it from interfering with bacterial cell wall synthesis. This resistance mechanism necessitates the use of penicillinase-resistant penicillins or other classes of antibiotics.

Question 5: Prednisone is prescribed for an acute asthma exacerbation. Which mechanism is responsible for its anti-inflammatory effect?

Directly inhibits COX-2 enzyme activity
Blocks H1 histamine receptors on mast cells
Binds glucocorticoid receptor → inhibits NF-κB → decreases cytokine transcription (Correct answer)
Stabilizes mast cell membranes via calcium channel blockade

Correct answer: Binds glucocorticoid receptor → inhibits NF-κB → decreases cytokine transcription

Glucocorticoids bind intracellular receptors that translocate to the nucleus and inhibit NF-κB, reducing transcription of pro-inflammatory cytokines and mediators.

Question 6: A 22-year-old woman comes to the physician because of a 10-day history of pain in multiple joints. She first had pain in her right elbow, and then her right shoulder, and now has pain, redness, and swelling in her left knee that began 2 days ago. She currently has no pain in the right shoulder and elbow. There is no history of trauma. She is sexually active, and she and her partner use condoms for contraception inconsistently. Examination of the left knee shows warmth, erythema, tenderness, and soft-tissue swelling. Range of motion of the knee is limited to 10 degrees of flexion. The remainder of the examination, including pelvic examination, shows no abnormalities. Arthrocentesis of the knee joint yields 10 mL of cloudy fluid with a leukocyte count of 18,300/mm3 (97% segmented neutrophils). Microscopic examination of the leukocytes within the joint fluid is most likely to show which of the following?

Gram-negative diplococci
Gram-positive cocci in clusters (Correct answer)
Acid-fast bacteria
Needle-shaped negatively birefringent crystals
Cuboidal positively birefringent crystals

Correct answer: Gram-positive cocci in clusters

The patient's migratory polyarthralgia followed by acute monoarthritis in a young, sexually active woman with inconsistent condom use strongly suggests disseminated gonococcal infection. However, the question asks for the *most likely* microscopic finding in the joint fluid. While Neisseria gonorrhoeae (gram-negative diplococci) is a strong clinical suspicion, Staphylococcus aureus (gram-positive cocci in clusters) remains the most common cause of septic arthritis overall, even in this demographic. Therefore, gram-positive cocci in clusters are the most likely finding on Gram stain of the synovial fluid.

Question 7: A previously healthy 2-year-old boy is brought to the emergency department because of bloody stools for 2 days. His vital signs are within normal limits. Abdominal examination shows no abnormalities. Laboratory studies show: Hemoglobin 11 g/dL Hematocrit 37% Leukocyte count 9500/mm3 Platelet count 250,000/mm3 Test of the stool for occult blood is positive. During an emergency laparotomy, a 3 × 2-cm protrusion is found on the antimesenteric border of the small intestine approximately 50 cm proximal to the ileocecal valve. Which of the following is the most likely cause of this patient’s condition?

Ectopic adrenal gland
Retrocecal appendix
Carcinoid tumor
Umbilical hernia
Meckel diverticulum (Correct answer)

Correct answer: Meckel diverticulum

The patient's presentation of painless bloody stools in a 2-year-old boy, combined with the surgical finding of a 3x2 cm protrusion on the antimesenteric border of the small intestine approximately 50 cm proximal to the ileocecal valve, is classic for a Meckel diverticulum. This congenital anomaly is a remnant of the omphalomesenteric duct, and often contains ectopic gastric or pancreatic tissue that can cause ulceration and bleeding.

Question 8: During a routine examination, a 25-year-old woman expresses concern about her risk for ovarian cancer because her mother died of the disease. Which of the following is the most appropriate course of action?

Annual CT scans of the abdomen
Recommend a diet high in beta-carotene
Prophylactic oophorectomy
Obtain a more detailed family history of cancer (Correct answer)
Reassure her that ovarian cancer is not hereditary

Correct answer: Obtain a more detailed family history of cancer

Ovarian cancer can have a hereditary component, particularly with a first-degree relative affected. Before providing reassurance or recommending drastic measures, it is essential to obtain a more detailed family history of cancer, including types of cancer, age of onset, and affected relatives, to assess the true genetic risk and determine if genetic counseling or testing is warranted.

Question 9: A 68-year-old man undergoes elective CABG. On postoperative day 3, his urine output drops to 15 mL/hr, creatinine rises from 1.0 to 2.8 mg/dL, and he remains hemodynamically stable. What is the most likely diagnosis?

Acute tubular necrosis (Correct answer)
Urinary tract obstruction
Contrast nephropathy
Pre-renal azotemia from hypovolemia

Correct answer: Acute tubular necrosis

Acute kidney injury peaking 48–72 hours after major cardiac surgery most commonly represents ischemic acute tubular necrosis from intraoperative hypoperfusion.

Question 10: Reticular fibers, which form the scaffolding of lymph nodes and the liver, are composed primarily of which collagen type?

Type III collagen (Correct answer)
Type II collagen
Type IV collagen
Type I collagen

Correct answer: Type III collagen

Reticular fibers are thin Type III collagen fibers that stain with silver and support hematopoietic and lymphoid organs.

Question 11: A 3-year-old presents with fever, drooling, and muffled voice. She refuses to move her neck. CT shows a rim-enhancing fluid collection posterior to the pharynx. Most likely organism?

Streptococcus pyogenes
Haemophilus influenzae type b
Staphylococcus aureus (Correct answer)
Anaerobic mixed flora

Correct answer: Staphylococcus aureus

Retropharyngeal abscesses in children are most commonly caused by Staphylococcus aureus, including MRSA.

Question 12: A 38-year-old woman presents with a 6-month history of intermittent rectal bleeding and a change in bowel habits. Colonoscopy reveals a 4-cm pedunculated polyp in the descending colon. Histology shows a tubulovillous adenoma with high-grade dysplasia but clear margins. What is the next step?

Surveillance colonoscopy in 3 years
Radiation therapy
Segmental colectomy
Surveillance colonoscopy in 1 year (Correct answer)

Correct answer: Surveillance colonoscopy in 1 year

Complete endoscopic removal of a polyp with high-grade dysplasia and clear margins warrants repeat colonoscopy at 1 year due to elevated adenoma recurrence risk.

Question 13: Parietal cells of the gastric fundus are characterized by an extensive tubulovesicular system and mitochondria. They secrete which substance?

Pepsinogen
Mucus
Hydrochloric acid and intrinsic factor (Correct answer)
Gastrin

Correct answer: Hydrochloric acid and intrinsic factor

Parietal (oxyntic) cells secrete HCl via H+/K+ ATPase and intrinsic factor necessary for vitamin B12 absorption in the ileum.

Question 14: A patient with a retropharyngeal abscess could have infection spread into the posterior mediastinum through which anatomical space?

Carotid space
Parapharyngeal space
Danger space (space 4) (Correct answer)
Masticator space

Correct answer: Danger space (space 4)

The danger space (space 4) lies between the alar and prevertebral fascia layers and extends from the skull base to the posterior mediastinum, providing a direct path for infection spread.

Question 15: A sexually active 37-year-old woman comes to the physician because of a 2-day history of pain in the area of her genitals. Pelvic examination shows shallow, small, extremely tender ulcers with red bases in the vulvar and vaginal regions. A Tzanck smear shows the presence of multinucleated giant cells. Which of the following infectious agents is the most likely cause of these findings?

Treponema pallidum
Herpes simplex virus (Correct answer)
Chlamydia trachomatis
Candida albicans
Trichomonas vaginalis

Correct answer: Herpes simplex virus

The presence of shallow, small, extremely tender ulcers with red bases in the vulvar and vaginal regions is highly characteristic of genital herpes. The finding of multinucleated giant cells on a Tzanck smear is a classic cytological hallmark of herpes simplex virus (HSV) infection, confirming the viral etiology. HSV causes painful vesicular lesions that rupture to form ulcers, and the Tzanck smear helps differentiate it from other causes of genital ulcers.

Question 16: A 22-year-old primigravida at 32 weeks has BP 158/106 mmHg, blurred vision, and 3+ proteinuria. Magnesium sulfate is administered. What is the primary therapeutic goal of magnesium in this clinical scenario?

Reduce maternal blood pressure to safe levels
Prevent eclamptic seizures (Correct answer)
Inhibit uterine contractions
Accelerate fetal lung maturity

Correct answer: Prevent eclamptic seizures

Magnesium sulfate is used as seizure prophylaxis (eclampsia prevention) in severe-range preeclampsia; it is not an effective antihypertensive agent.

Question 17: In the West lung zones, which pressure relationship defines Zone 1?

Arterial > alveolar > venous
Venous > arterial > alveolar
Arterial > venous > alveolar
Alveolar > arterial > venous (Correct answer)

Correct answer: Alveolar > arterial > venous

Zone 1 (lung apex) has alveolar pressure exceeding arterial pressure, collapsing capillaries and creating dead space with no gas exchange.

Question 18: A child is brought to the ER after ingesting penicillin tablets. Allergic reaction to penicillin is most commonly mediated by which mechanism?

Type II (cytotoxic) hypersensitivity
Type III (immune complex) hypersensitivity
Type I (IgE-mediated) hypersensitivity (Correct answer)
Type IV (delayed-type) hypersensitivity

Correct answer: Type I (IgE-mediated) hypersensitivity

The most common and clinically significant penicillin reactions are IgE-mediated (Type I), which can cause anaphylaxis within minutes of exposure.

Question 19: At autopsy, the heart of a 30-year-old man weighs 550 g. The left ventricle is dilated and hypertrophied. The aortic root is markedly dilated, and the aortic valve cusps are intact. The external iliac arteries contain irregular, focal cystic areas within the media with pools of mucopolysaccharide and fraying fragmentation of the elastica. Which of the following is the most likely diagnosis?

Marfan syndrome (Correct answer)
Cardiovascular syphilis
Ankylosing spondylitis
Osteogenesis imperfecta, type II (recessive)
Systemic lupus erythematosus

Correct answer: Marfan syndrome

The combination of a dilated and hypertrophied left ventricle, markedly dilated aortic root, and specific arterial changes (cystic medial necrosis with mucopolysaccharide pools and elastica fragmentation) in a young man is highly indicative of Marfan syndrome. This genetic disorder affects connective tissue due to a mutation in the FBN1 gene, leading to characteristic cardiovascular manifestations like aortic root dilation and dissection.

Question 20: An 82-year-old man is admitted to the hospital because nursing staff in his skilled nursing care facility report that he has appeared sad and depressed during the past 2 months. It is reported that he has a history of psychiatric illness, but details are not provided. He has been taking olanzapine, paroxetine, and haloperidol for 2 years. He does not appear to be in acute distress. He is 160 cm (5 ft 3 in) tall and weighs 48 kg (105 lb); BMI is 19 kg/m2 . Physical examination shows 2+ cogwheel rigidity of the upper extremities. Neurologic examination shows psychomotor retardation. On mental status examination, he is alert and generally pleasant and cooperative. His affect has little intensity or range. He says he does not feel depressed or anxious. Laboratory findings are within the reference range. Which of the following is the most likely cause of this patient’s current symptoms?

Dementia, Alzheimer type
Major depressive disorder
Adjustment disorder
Drug-induced parkinsonism (Correct answer)
Akathisia

Correct answer: Drug-induced parkinsonism

The patient's new onset of cogwheel rigidity, psychomotor retardation, and flat affect, despite denying depression, are classic extrapyramidal symptoms consistent with parkinsonism. Given his medication regimen including haloperidol (a typical antipsychotic) and olanzapine (an atypical antipsychotic, but still with D2 antagonism), drug-induced parkinsonism is the most likely cause. These medications block dopamine D2 receptors, leading to a functional dopamine deficiency that mimics Parkinson's disease.

Question 21: A 45-year-old executive has a pervasive pattern of grandiosity, requires excessive admiration, lacks empathy, and reacts to criticism with rage. Which personality disorder best describes him?

Obsessive-compulsive personality disorder
Histrionic personality disorder
Antisocial personality disorder
Narcissistic personality disorder (Correct answer)

Correct answer: Narcissistic personality disorder

Narcissistic personality disorder is characterized by grandiosity, need for admiration, lack of empathy, and a sense of entitlement.

Question 22: A competitive inhibitor is added to an enzyme with Km = 2 mM and Vmax = 100 μmol/min. Which effect best describes the result?

Km increases, Vmax unchanged (Correct answer)
Km unchanged, Vmax decreases
Both Km and Vmax decrease
Both Km and Vmax increase

Correct answer: Km increases, Vmax unchanged

Competitive inhibitors bind the active site reversibly, raising apparent Km but leaving Vmax unchanged since excess substrate can outcompete the inhibitor.

Question 23: A 6-year-old boy has a large intra-abdominal mass in the midline just above the symphysis pubis. During an operation, a cystic mass is found attached to the umbilicus and the apex of the bladder. Which of the following is the most likely diagnosis?

Meckel cyst
Urachal cyst (Correct answer)
Hydrocele
Meckel diverticulum
Omphalocele

Correct answer: Urachal cyst

The urachus is an embryonic remnant of the allantois that connects the fetal bladder to the umbilicus. If the urachus fails to involute completely, it can form a cyst, which is typically located in the midline between the umbilicus and the bladder apex, precisely matching the description of the mass found in this patient.

Question 24: A patient requires a loading dose of a drug to rapidly achieve therapeutic plasma levels. Which pharmacokinetic parameter primarily determines the loading dose?

Bioavailability (F)
Clearance (CL)
Half-life (t½)
Volume of distribution (Vd) (Correct answer)

Correct answer: Volume of distribution (Vd)

Loading dose = (Target concentration × Vd) / F; a large Vd means the drug distributes widely into tissues and requires a larger loading dose to achieve the desired plasma concentration.

Question 25: A 30-year-old man with no psychiatric history suddenly believes he is receiving special messages from the television. He also hears voices commenting on his actions. Symptoms have been present for 3 weeks. What is the most likely diagnosis?

Brief psychotic disorder
Delusional disorder
Schizophreniform disorder (Correct answer)
Schizophrenia

Correct answer: Schizophreniform disorder

Schizophreniform disorder presents with schizophrenia-like symptoms lasting 1–6 months; duration less than 1 month is brief psychotic disorder.

Question 26: A 22-year-old man is brought to the emergency department because of a 6-hour history of severe, sharp, upper back pain. He has had progressive fatigue during the past 3 weeks. He is 183 cm (6 ft) tall and weighs 79 kg (175 lb); BMI is 24 kg/m2 . His temperature is 36.9°C (98.5°F), pulse is 90/min, and blood pressure is 160/55 mm Hg. Physical examination shows long, thin upper and lower extremities. Fingertip to fingertip with arms outstretched is 189 cm (74 in) wide. A high-pitched midsystolic click is heard predominantly over the apex. Which of the following best describes the primary genetic cause of this patient’s condition?

Overexpression of fibronectin gene
Mutation in keratin-14 gene
Expression of genomic duplication within the fibrin gene
Nonsense mutation in fibrillin-1 gene (Correct answer)
Overexpression of collagen X gene

Correct answer: Nonsense mutation in fibrillin-1 gene

The patient's features, including tall stature, long extremities (arm span greater than height), and cardiovascular findings like a midsystolic click (mitral valve prolapse) and wide pulse pressure (suggesting aortic root dilation), are classic for Marfan syndrome. This is an autosomal dominant disorder caused by mutations in the *FBN1* gene, which encodes fibrillin-1, a crucial component of elastic fibers in connective tissue. A nonsense mutation would lead to a truncated, non-functional protein.

Question 27: A 38-year-old man comes to the physician because of a 6-month history of occasional episodes of chest tightness, wheezing, and cough. The symptoms are often mild and resolve spontaneously. He has been otherwise healthy. His respirations are 13/min. The lungs are clear to auscultation. Cardiac examination and chest x-ray show no abnormalities. Which of the following agents is most appropriate to treat acute episodes in this patient?

Cromolyn
Ipratropium
Beclomethasone
Theophylline
Albuterol (Correct answer)

Correct answer: Albuterol

The patient's symptoms of occasional, mild, and spontaneously resolving chest tightness, wheezing, and cough are consistent with mild intermittent asthma. For acute episodes of asthma, the most appropriate treatment is a short-acting beta-2 adrenergic agonist (SABA) like albuterol. Albuterol rapidly relaxes bronchial smooth muscle, leading to bronchodilation and quick relief of symptoms.

Question 28: Schwann cells in the peripheral nervous system primarily function to:

Phagocytose cellular debris in the CNS
Produce cerebrospinal fluid
Myelinate peripheral axons to increase conduction velocity (Correct answer)
Regulate synaptic neurotransmitter levels

Correct answer: Myelinate peripheral axons to increase conduction velocity

Schwann cells wrap peripheral axons in myelin sheaths, enabling saltatory conduction and dramatically increasing action potential propagation speed.

Question 29: The endothelium lining blood vessels is classified as which epithelial type?

Simple squamous (Correct answer)
Stratified squamous
Simple columnar
Simple cuboidal

Correct answer: Simple squamous

Vascular endothelium is simple squamous epithelium (mesothelial origin), forming a smooth, low-friction lining that minimizes turbulence.

Question 30: A 38-year-old woman with an 18-year history of type 1 diabetes mellitus and progressive renal failure is being considered for dialysis. Laboratory studies show normocytic, normochromic anemia. Which of the following medications is most appropriate to treat the anemia in this patient?

Erythropoietin (Correct answer)
Folic acid
Folinic acid
Vitamin B1 (thiamine)
Vitamin B12 (cyanocobalamin)

Correct answer: Erythropoietin

Patients with chronic renal failure, such as those with progressive renal failure due to type 1 diabetes, often develop normocytic, normochromic anemia. This is primarily due to decreased production of erythropoietin by the damaged kidneys. Erythropoietin is a hormone that stimulates red blood cell production in the bone marrow, making exogenous erythropoietin the most appropriate treatment for this type of anemia.

Question 31: A 14-year-old female presents with fatigue, cold intolerance, weight gain, and a diffusely enlarged, non-tender thyroid. TSH is elevated; free T4 is low. Anti-TPO antibodies are positive. Diagnosis?

Graves disease
De Quervain thyroiditis
Hashimoto thyroiditis (Correct answer)
Thyroid lymphoma

Correct answer: Hashimoto thyroiditis

Hashimoto thyroiditis is the most common cause of hypothyroidism in children and adolescents, characterized by anti-TPO antibodies and goiter.

Question 32: A 3-year-old girl is brought to the emergency department because of left leg pain after falling at preschool 2 hours ago. She has a history of fractures after minor trauma. She has consistently been at the 10th percentile for height and weight since birth. Examination shows blue sclerae. There is an obvious deformity of the left thigh. An x-ray shows a new fracture of the left femur and evidence of previous fracturing. Which of the following is the most likely cause of these findings?

Hypophosphatemia
Child abuse
Hypocalcemia
Defective type I collagen (Correct answer)
Deficient sulfate ion transport
Vitamin D deficiency

Correct answer: Defective type I collagen

The classic triad of multiple fractures from minor trauma, blue sclerae, and short stature is highly indicative of osteogenesis imperfecta (OI). OI is a genetic disorder caused by mutations in genes encoding type I collagen, which is a major component of bone, sclerae, and other connective tissues. The defective collagen leads to brittle bones and the characteristic blue discoloration of the sclerae due to the underlying choroidal veins showing through the thin, translucent sclera.

Question 33: A 38-year-old woman presents with 6 weeks of depressed mood, hypersomnia, weight gain, psychomotor retardation, and inability to concentrate. She denies any prior manic episodes. Which treatment is first-line for moderate-to-severe major depressive disorder?

SSRI monotherapy (e.g., sertraline) (Correct answer)
Tricyclic antidepressant
Bupropion plus lithium
Benzodiazepine for 2 weeks

Correct answer: SSRI monotherapy (e.g., sertraline)

SSRIs are first-line pharmacotherapy for major depressive disorder due to their efficacy, tolerability, and favorable side-effect profile.

Question 34: A biopsy of a lymph node shows Reed-Sternberg cells with an 'owl-eye' appearance. Flow cytometry shows CD15+/CD30+/CD45- cells. What is the diagnosis?

Diffuse large B-cell lymphoma
Classic Hodgkin lymphoma (Correct answer)
Burkitt lymphoma
Anaplastic large cell lymphoma

Correct answer: Classic Hodgkin lymphoma

Classic Hodgkin lymphoma Reed-Sternberg cells are CD15+, CD30+, and characteristically CD45- (leukocyte common antigen negative).

Question 35: A 25-year-old woman has a thyroid mass. Histology shows papillae with fibrovascular cores, ground-glass 'Orphan Annie eye' nuclei, and intranuclear inclusions. What is the most common mutation?

BRAF V600E point mutation (Correct answer)
RAS mutation
RET/PTC rearrangement
PAX8-PPAR gamma fusion

Correct answer: BRAF V600E point mutation

BRAF V600E mutation is found in ~60% of papillary thyroid carcinomas and is associated with the characteristic nuclear features of this tumor.

Question 36: A 22-year-old type 1 diabetic presents with vomiting, abdominal pain, and fruity breath. ABG shows pH 7.22, HCO3 10 mEq/L, glucose 480 mg/dL. What is the priority initial treatment?

Potassium replacement only
Insulin bolus IV
Sodium bicarbonate IV
IV isotonic saline fluid resuscitation (Correct answer)

Correct answer: IV isotonic saline fluid resuscitation

Fluid resuscitation with IV isotonic saline is the first priority in DKA to correct volume depletion before initiating insulin.

Question 37: A 30-year-old woman develops acute paraplegia, bilateral Babinski signs, and a sensory level at T6, with bladder dysfunction, 2 weeks after a viral illness. MRI shows T2 signal change spanning 3+ vertebral segments. What is the most likely diagnosis?

Epidural abscess
Multiple sclerosis
Transverse myelitis (Correct answer)
Spinal cord infarction

Correct answer: Transverse myelitis

Acute transverse myelitis presents with bilateral motor, sensory, and autonomic dysfunction with a sensory level, often post-infectious, with longitudinally extensive T2 MRI changes.

Question 38: A 32-year-old man comes to the physician because of a 12-day history of abdominal cramps and bloating, diarrhea, and flatulence. He says that he started a new exercise program 2 weeks ago and has been consuming a high quantity of yogurt bars, peanut butter, and protein- and calorie-enriched milk shakes to “bulk up.” He has no history of serious illness and takes no medications. His temperature is 37°C (98.6°F). The abdomen is distended, nontender, and tympanitic to percussion. Bowel sounds are increased. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of this patient’s symptoms?

Fungal overgrowth in the small bowel
Allergy to peanuts
Irritable bowel syndrome
Lactase deficiency (Correct answer)
Incarcerated hernia

Correct answer: Lactase deficiency

The patient's symptoms of abdominal cramps, bloating, diarrhea, and flatulence, which began after increasing his consumption of dairy-containing products like yogurt bars and milkshakes, are highly suggestive of lactase deficiency (lactose intolerance). This condition results from the inability to digest lactose, leading to its fermentation by gut bacteria and the production of gas and osmotic diarrhea.

Question 39: The blood flow through an organ is measured while the perfusion pressure is varied experimentally. An abrupt, sustained increase in perfusion pressure increases flow initially, but over the course of 1 minute, the flow returns nearly to the baseline level despite continued elevation of the perfusion pressure. The organ under study is exhibiting which of the following?

Ischemia
Active hyperemia
Autoregulation (Correct answer)
Reactive hyperemia

Correct answer: Autoregulation

This phenomenon describes autoregulation, the intrinsic ability of an organ or tissue to maintain a relatively constant blood flow despite changes in perfusion pressure. When perfusion pressure increases, the blood vessels in an autoregulating organ constrict (myogenic response) or release vasoconstrictors. This increases resistance and returns blood flow towards its baseline level, ensuring stable nutrient and oxygen delivery.

Question 40: A 26-year-old G1P0 at 16 weeks undergoes amniocentesis. Results show markedly elevated amniotic fluid AFP and a positive acetylcholinesterase. What is the most likely diagnosis?

Turner syndrome (45,X)
Open neural tube defect (Correct answer)
Trisomy 21 (Down syndrome)
Trisomy 18

Correct answer: Open neural tube defect

Elevated amniotic AFP combined with positive acetylcholinesterase is diagnostic of an open neural tube defect, confirming fetal neural tissue is exposed to amniotic fluid.

Question 41: A 48-year-old man presents with jaundice and a palpable, non-tender gallbladder. CT shows a mass in the head of the pancreas. What embryologic structure gives rise to most pancreatic ductal adenocarcinomas?

Islet cells from neural crest
Hepatic diverticulum
Pancreatic ductal epithelium derived from foregut endoderm (Correct answer)
Pancreatic acinar cells from mesoderm

Correct answer: Pancreatic ductal epithelium derived from foregut endoderm

Pancreatic ductal adenocarcinoma arises from ductal epithelium of foregut endoderm origin and commonly obstructs the common bile duct when in the head of the pancreas.

Question 42: A 45-year-old man comes to the physician because of fever and night sweats for 8 days. He has Crohn disease treated with infliximab. His temperature is 39°C (102.2°F). Physical examination shows diffuse cervical lymphadenopathy. A biopsy specimen of the nodes shows caseating granulomas. No organisms are identified on Gram stain. Which of the following is the most likely causal organism?

Treponema pallidum
Brucella abortus
Aspergillus niger
Francisella tularensis
Mycobacterium tuberculosis (Correct answer)

Correct answer: Mycobacterium tuberculosis

The patient's symptoms of fever, night sweats, and lymphadenopathy are consistent with tuberculosis. Crucially, his treatment with infliximab, a TNF-α inhibitor, significantly increases the risk of reactivation of latent tuberculosis. The biopsy finding of caseating granulomas is pathognomonic for tuberculosis, even if organisms are not identified on Gram stain (Mycobacterium tuberculosis is acid-fast, not Gram-stain positive). Therefore, Mycobacterium tuberculosis is the most likely causal organism.

Question 43: A 10-day-old formula-fed neonate develops bilious vomiting. X-ray shows a 'double bubble' sign. The most likely diagnosis is:

Hirschsprung disease
Pyloric stenosis
Duodenal atresia (Correct answer)
Midgut volvulus

Correct answer: Duodenal atresia

The double bubble sign (dilated stomach + proximal duodenum) is pathognomonic for duodenal atresia.

Question 44: A 21-year-old woman comes to the physician for counseling prior to conception. She delivered a female newborn with anencephaly 1 year ago. The newborn died at the age of 4 days. She asks the physician if she can take any vitamins to decrease her risk for conceiving a fetus with anencephaly. It is most appropriate for the physician to recommend which of the following vitamins?

Vitamin B2 (riboflavin)
Vitamin B6 (pyridoxine)
Vitamin B1 (thiamine)
Vitamin B12 (cyanocobalamin)
Biotin
Folic acid (Correct answer)

Correct answer: Folic acid

Anencephaly is a severe neural tube defect (NTD) that occurs during early fetal development. Supplementation with folic acid (vitamin B9) before conception and during the first trimester of pregnancy has been extensively proven to significantly reduce the risk of NTDs. Folic acid is crucial for DNA synthesis and repair, and for cell division, which are vital processes during neural tube closure.

Question 45: A 35-year-old vegetarian woman presents with fatigue and pallor. Labs: Hgb 9.2, MCV 110, hypersegmented neutrophils on smear. Serum B12 is low. Which additional finding would suggest pernicious anemia as the cause?

Elevated serum ferritin
Low reticulocyte count
Elevated homocysteine only
Positive anti-intrinsic factor antibodies (Correct answer)

Correct answer: Positive anti-intrinsic factor antibodies

Anti-intrinsic factor antibodies are highly specific for pernicious anemia, distinguishing it from dietary B12 deficiency.

Question 46: A 65-year-old man undergoes a low anterior resection for rectal cancer. Three days post-op he develops fever, tachycardia, leukocytosis, and purulent output from a pelvic drain. CT confirms an anastomotic leak with contained pelvic abscess. He is hemodynamically stable. What is the appropriate management?

CT-guided drainage, IV antibiotics, and proximal diversion if needed (Correct answer)
IV antibiotics alone
Immediate re-laparotomy and Hartmann's procedure
Colonoscopic placement of a covered stent

Correct answer: CT-guided drainage, IV antibiotics, and proximal diversion if needed

A contained anastomotic leak in a stable patient is managed with CT-guided drainage, IV antibiotics, and fecal diversion if the anastomosis cannot be salvaged.

Question 47: Which dopaminergic pathway is most associated with the positive symptoms of schizophrenia?

Tuberoinfundibular pathway
Mesocortical pathway
Nigrostriatal pathway
Mesolimbic pathway (Correct answer)

Correct answer: Mesolimbic pathway

Hyperactivity of the mesolimbic dopaminergic pathway (VTA to nucleus accumbens/limbic areas) underlies the positive symptoms (hallucinations, delusions) of schizophrenia.

Question 48: A study reports a p-value of 0.03 with alpha set at 0.05. What is the correct interpretation?

There is a 3% probability the null hypothesis is true
The study has 97% statistical power
The finding is clinically significant
There is a 3% probability of obtaining results this extreme if the null hypothesis is true (Correct answer)

Correct answer: There is a 3% probability of obtaining results this extreme if the null hypothesis is true

A p-value represents the probability of observing results at least as extreme as those found, assuming the null hypothesis is true — not the probability that the null is true.

Question 49: A 25-year-old man with Marfan syndrome ruptures his aorta. Histology shows fragmentation of elastic fibers and increased ground substance in the media. What is this finding called?

Cystic medial necrosis (medionecrosis) (Correct answer)
Monckeberg medial sclerosis
Fibromuscular dysplasia
Atherosclerosis

Correct answer: Cystic medial necrosis (medionecrosis)

Cystic medial necrosis describes degeneration of elastic tissue and smooth muscle in the aortic media with mucoid material accumulation, seen in Marfan syndrome and hypertension.

Question 50: A 17-year-old girl is brought to the physician by her parents 30 minutes after having a generalized tonic-clonic seizure while playing in a soccer game. She currently takes no medications. Physical examination shows no abnormalities. After further testing including 24-hour continuous EEG monitoring, carbamazepine is prescribed. This patient’s use of additional medications should be monitored because of which of the following changes in drug disposition after starting pharmacotherapy?

Increased excretion by the kidneys
Decreased absorption in the intestine
Decreased distribution to the brain
Increased recirculation in the bile
Increased metabolism by the liver (Correct answer)

Correct answer: Increased metabolism by the liver

Carbamazepine is a potent inducer of hepatic cytochrome P450 enzymes, particularly CYP3A4. This enzyme induction leads to increased metabolism of many co-administered drugs, as well as carbamazepine itself. Consequently, the plasma concentrations of other medications taken by the patient may decrease, potentially reducing their efficacy and requiring dose adjustments.

Question 51: Damage to Wernicke's area results in which type of aphasia?

Non-fluent aphasia with good comprehension
Pure word deafness with intact reading
Global aphasia with intact repetition
Fluent aphasia with poor comprehension (Correct answer)

Correct answer: Fluent aphasia with poor comprehension

Wernicke's aphasia (posterior superior temporal gyrus, dominant hemisphere) produces fluent but paraphasic speech with severely impaired comprehension and repetition.

Question 52: Which is the rate-limiting enzyme of cholesterol biosynthesis and the target of statin drugs?

Squalene synthase
HMG-CoA synthase
Lanosterol synthase
HMG-CoA reductase (Correct answer)

Correct answer: HMG-CoA reductase

HMG-CoA reductase converts HMG-CoA to mevalonate; it is the committed, rate-limiting step targeted by statins to lower cholesterol.

Question 53: A 25-year-old woman reports chronic feelings of emptiness, frantic efforts to avoid abandonment, and a history of self-cutting when upset. She has had three suicide attempts. What personality disorder best fits?

Narcissistic personality disorder
Borderline personality disorder (Correct answer)
Histrionic personality disorder
Antisocial personality disorder

Correct answer: Borderline personality disorder

Borderline personality disorder is defined by unstable mood, identity, and relationships, chronic emptiness, fear of abandonment, self-harm, and impulsivity.

Question 54: A 57-year-old woman with inoperable small cell carcinoma of the lung has had lethargy, loss of appetite, and nausea for 1 week. She received radiation therapy 2½ years ago. She has stable angina pectoris controlled with nitrates. Her pulse is 68/min, respirations are 16/min, and blood pressure is 118/72 mm Hg. There is no jugular venous distention, and skin turgor is normal. She is oriented to person and place but not to time. Laboratory studies show: Serum Na+ 128 mEq/L Cl- 100 mEq/L K + 4.2 mEq/L HCO3 - 24 mEq/L Urea nitrogen 11 mg/dL Glucose 92 mg/dL Creatinine 0.8 mg/dL Osmolality 270 mOsmol/kg H2O Urine Na+ 78 mEq/L Osmolality 310 mOsmol/kg H2O An x-ray of the chest shows a mass in the right upper lobe of the lung that is unchanged from an x-ray taken 3 months ago. Which of the following is the most likely explanation for these findings?

Syndrome of inappropriate secretion of ADH (vasopressin) (Correct answer)
Hypothyroidism
Surreptitious use of diuretics
Congestive heart failure
Compulsive water drinking

Correct answer: Syndrome of inappropriate secretion of ADH (vasopressin)

The patient has hyponatremia (Na+ 128) with a low serum osmolality (270) and inappropriately concentrated urine (Urine Osmolality 310, Urine Na+ 78), despite being euvolemic (normal skin turgor, no JVD). These findings are classic for SIADH. Small cell lung carcinoma is a well-known paraneoplastic cause of SIADH, where tumor cells ectopically produce ADH, leading to excessive water reabsorption and dilutional hyponatremia, causing symptoms like lethargy and nausea.

Question 55: A 45-year-old man has had a 1-week history of increasing neck pain when he turns his head to the right. He also has had a pins-and-needles sensation starting in the neck and radiating down the right arm into the thumb. His symptoms began 3 months ago when he developed severe pain in the neck and right shoulder. Neurologic examination shows limitation of motion on turning the neck to the right. There is 4+/5 weakness of the right biceps and decreased pinprick over the right thumb. Deep tendon reflexes are 1+ in the right biceps and brachioradialis; all others are 2+. Which of the following is the most likely diagnosis?

Ulnar nerve compression
Carpal tunnel syndrome
Thoracic outlet syndrome
Cervical root compression (Correct answer)
Multiple sclerosis

Correct answer: Cervical root compression

The patient's symptoms of neck pain radiating into the arm and thumb, associated with weakness in the biceps and decreased sensation in the thumb, along with diminished biceps and brachioradialis reflexes, are highly localized to the C6 nerve root. This pattern of dermatomal and myotomal deficits, exacerbated by neck movement, is characteristic of cervical radiculopathy, most commonly caused by compression of a cervical nerve root due to a herniated disc or osteophyte.

Question 56: A Gram-negative diplococcus is isolated from urethral discharge of a sexually active male. The organism grows on Thayer-Martin agar and is oxidase-positive. Which virulence factor allows this organism to evade phagocyte killing?

Leukocidin
Coagulase
IgA protease (Correct answer)
Protein A

Correct answer: IgA protease

Neisseria gonorrhoeae produces IgA protease, which cleaves secretory IgA and helps the organism evade mucosal immune defenses.

Question 57: An increased concentration of fructose 2,6-bisphosphate in hepatocytes will have a positive regulatory effect on which of the following?

Glycolysis and phosphofructokinase 1 (Correct answer)
Glycolysis and glucokinase
Gluconeogenesis and glucose-6-phosphatase
Gluconeogenesis and phosphoenolpyruvate carboxykinase

Correct answer: Glycolysis and phosphofructokinase 1

Fructose 2,6-bisphosphate is a potent allosteric activator of phosphofructokinase-1 (PFK-1), the rate-limiting enzyme in glycolysis. By increasing PFK-1 activity, it promotes the conversion of fructose-6-phosphate to fructose 1,6-bisphosphate, thereby stimulating the glycolytic pathway. Conversely, it inhibits fructose 1,6-bisphosphatase, an enzyme in gluconeogenesis, ensuring that glycolysis is favored when its concentration is high.

Question 58: A previously healthy 28-year-old man dies in a motor vehicle collision. At autopsy, the kidneys are enlarged bilaterally, and each weighs 3 kg. The external surface of the kidneys appears to be a mass of cysts. Microscopic examination of the kidneys shows intact nephrons interspersed between the cysts. The most likely cause of these changes in the kidneys involves which of the following modes of inheritance?

Chromosome 22q11.2 deletion
Autosomal dominant (Correct answer)
X-linked
Mitochondrial
Autosomal recessive

Correct answer: Autosomal dominant

The autopsy findings of massively enlarged, cystic kidneys with intact nephrons in a young adult are characteristic of Autosomal Dominant Polycystic Kidney Disease (ADPKD). This genetic disorder, caused by mutations in PKD1 or PKD2 genes, leads to the progressive development of numerous fluid-filled cysts that eventually destroy renal parenchyma. It is the most common inherited kidney disease and typically manifests in adulthood.

Question 59: A 4-year-old presents with periorbital edema, frothy urine, and hypoalbuminemia. Urine dipstick shows 4+ protein with no blood. Most likely diagnosis?

Focal segmental glomerulosclerosis
Post-streptococcal GN
IgA nephropathy
Minimal change disease (Correct answer)

Correct answer: Minimal change disease

Minimal change disease is the most common cause of nephrotic syndrome in children aged 1–8 and responds to steroids.

Question 60: A 47-year-old woman is brought to the physician by her husband because of bizarre behavior for 1 week. Her husband says that she makes no sense when she speaks and seems to be seeing things. She also has had difficulty sleeping for 2 months and has gained approximately 9 kg (20 lb) during the past 5 months. During this time, she has been moody and easily fatigued. He also notes that the shape of her face has become increasingly round and out of proportion with the rest of her body despite her weight gain. She has no history of psychiatric or medical illness. She is 160 cm (5 ft 3 in) tall and weighs 70 kg (155 lb); BMI is 28 kg/m2 . Her pulse is 98/min, respirations are 8/min, and blood pressure is 148/92 mm Hg. Physical examination shows truncal obesity and ecchymoses over the upper and lower extremities. Neurologic examination shows no focal findings. Mental status examination shows pressured speech and a disorganized thought process. There is evidence of visual and auditory hallucinations. Urine toxicology screening is negative. Which of the following is the most likely diagnosis?

Schizotypal personality disorders
Major depressive disorder with psychotic features
Schizophrenia
Psychotic disorder due to a general medical condition (Correct answer)
Brief psychotic disorder

Correct answer: Psychotic disorder due to a general medical condition

The patient presents with acute psychotic symptoms (hallucinations, disorganized thought, pressured speech) alongside several physical signs highly suggestive of Cushing's syndrome, including a round face, truncal obesity, ecchymoses, weight gain, and hypertension. The rapid onset of psychosis in the context of these clear physical findings points to a general medical condition, likely Cushing's, as the underlying cause of her psychiatric symptoms.

Question 61: A 77-year-old woman is visited by the home care nurse who notes that the patient is more lethargic than usual. Her skin and mucous membranes are dry. An increase in the serum concentration or activity of which of the following provides the strongest indication that the patient is dehydrated?

Calcium
Bilirubin
Uric acid
Alkaline phosphatase
Albumin (Correct answer)

Correct answer: Albumin

Dehydration causes a reduction in plasma volume, leading to hemoconcentration. Albumin is a large protein that remains within the intravascular space. When plasma volume decreases due to dehydration, the concentration of albumin in the serum increases because the same amount of albumin is now dissolved in a smaller volume of fluid, making it a strong indicator of dehydration.

Question 62: A 32-year-old woman undergoing IVF achieves a positive β-hCG two weeks after embryo transfer. She presents with severe abdominal distension, dyspnea, and 6 kg weight gain over 5 days. What is the most likely diagnosis?

Ruptured ectopic pregnancy
Heterotopic pregnancy
Ovarian torsion
Ovarian hyperstimulation syndrome (OHSS) (Correct answer)

Correct answer: Ovarian hyperstimulation syndrome (OHSS)

OHSS is a complication of ovarian stimulation characterized by massive fluid shifts, ascites, weight gain, and dyspnea, worsened by the rise in hCG from an established pregnancy.

Question 63: Berkson's bias is a specific type of selection bias most likely to occur in:

Population-based cross-sectional surveys
Hospital-based case-control studies (Correct answer)
Prospective cohort studies
Randomized controlled trials

Correct answer: Hospital-based case-control studies

Berkson's bias arises when hospitalized controls differ systematically from the general population, distorting the exposure-disease association in hospital-based case-control studies.

Question 64: A 24-year-old at 28 weeks with gestational diabetes has a growth ultrasound showing estimated fetal weight at the 97th percentile with a disproportionately large abdominal circumference. This finding is most directly caused by which fetal mechanism?

Fetal glucagon excess stimulating hepatic glycogen
Fetal hyperinsulinemia causing increased fat deposition (Correct answer)
Fetal hyperglycemia causing osmotic fluid shifts
Placental insufficiency causing growth acceleration

Correct answer: Fetal hyperinsulinemia causing increased fat deposition

Maternal hyperglycemia leads to fetal hyperinsulinemia, which acts as a growth factor causing macrosomia through increased fat and glycogen deposition.

Question 65: A 20-year-old woman is brought to the emergency department 20 minutes after being stung by a wasp. She says that she feels a lump in her throat and chest tightness. She has a history of allergy to wasp venom. Her pulse is 120/min, and blood pressure is 80/40 mm Hg. Physical examination shows eruptions that coalesce into giant urticaria. There is audible wheezing. Which of the following best describes the cause of this patient’s reaction?

Activation of macrophages by soluble immune complexes
Induction of a cytotoxic reaction by CD8+ T lymphocytes
Binding of antigen to preexisting cell-fixed IgE antibodies (Correct answer)
Formation of IgM antibodies against cell surface receptor antigens
Formation of IgG antibodies against extracellular matrix antigen

Correct answer: Binding of antigen to preexisting cell-fixed IgE antibodies

This patient is experiencing anaphylaxis, a severe, systemic Type I hypersensitivity reaction. This reaction is mediated by IgE antibodies, which are pre-formed and fixed to the surface of mast cells and basophils. Upon re-exposure to the allergen (wasp venom), the antigen binds to these cell-fixed IgE antibodies, triggering degranulation and the rapid release of inflammatory mediators like histamine, leading to the observed symptoms.

Question 66: A premature infant born at 28 weeks develops increasing respiratory distress immediately after birth. CXR shows diffuse ground-glass opacities bilaterally. The deficiency responsible is:

Pulmonary IgA
Alpha-1 antitrypsin
Clara cell secretory protein
Surfactant (Correct answer)

Correct answer: Surfactant

Respiratory distress syndrome in premature infants results from surfactant deficiency, which reduces alveolar surface tension.

Question 67: A 27-year-old woman comes to the physician because of a 3-week history of fatigue and blurred vision. She occasionally has had double vision during this period. For the past year, she has had 3- to 4-day episodes of numbness and tingling of her arms and legs. She has no personal or family history of serious illness. Her only medication is an oral contraceptive. She has smoked one pack of cigarettes daily for 5 years. Vital signs are within normal limits. Funduscopic examination shows no abnormalities. Visual acuity is decreased in the left eye. Sensation to light touch is decreased over the hands and feet; sensation to pinprick is increased over the fingers and toes bilaterally. An MRI of the brain shows several hyperintense oval plaques in the periventricular region on T2-weighted images. Which of the following is the most likely diagnosis?

Toxoplasmosis
Glioma
Multiple sclerosis (Correct answer)
Guillain-Barré syndrome
Systemic lupus erythematosus

Correct answer: Multiple sclerosis

The patient's recurrent neurological symptoms, such as fatigue, blurred vision, double vision, and episodes of numbness/tingling in different areas (disseminated in time and space), are highly suggestive of multiple sclerosis. The MRI findings of hyperintense oval plaques in the periventricular region on T2-weighted images are characteristic demyelinating lesions seen in MS. This combination of clinical presentation and imaging findings strongly supports the diagnosis.

Question 68: A 57-year-old man comes to the physician accompanied by his wife because of a 2-year history of fatigue. He reports waking up tired nearly every morning, often with a headache. He naps almost every afternoon. He thinks that the fatigue is affecting his concentration and performance at work. His wife says that he snores frequently during the night and sometimes wakes up gasping for air. She describes him as a restless sleeper. His tonsils and adenoids were removed when he was a child. He has no history of serious illness and takes no medications. He is 178 cm (5 ft 10 in) tall and weighs 115 kg (253 lb); BMI is 36 kg/m2 . His pulse is 86/min, and blood pressure is 164/88 mm Hg. The nasal septum is at the midline. Examination shows no other abnormalities. Which of the following is the most likely diagnosis?

REM sleep behavior disorder
hronic fatigue syndrome
Narcolepsy
Sleep apnea (Correct answer)
Restless legs syndrome

Correct answer: Sleep apnea

The patient's chronic fatigue, daytime sleepiness, morning headaches, and impaired concentration, combined with his wife's report of frequent snoring and waking up gasping for air, are classic symptoms of obstructive sleep apnea. His obesity (BMI 36 kg/m2) and hypertension are significant risk factors for this condition, making sleep apnea the most likely diagnosis.

Question 69: A 14-year-old girl is brought to the physician because of a recent growth spurt of 15 cm (6 in) during the past year. She also has had increasing fatigue and palpitations during this period. Her paternal aunt has a history of palpitations and severe myopia. She is at the 95th percentile for height and 50th percentile for weight. Physical examination shows a long, thin face. Ophthalmologic examination shows dislocated lenses. Cardiac examination shows a hyperdynamic precordium with early click and systolic murmur. Echocardiography shows an enlarged aortic root and mitral valve prolapse. Abnormal synthesis of which of the following proteins is the most likely cause of this patient’s disorder?

Collagen, type I
Elastin
PAX 6
Fibrillin-1 (Correct answer)
Fibroblast growth factor R3
Laminin
Neurofibromin

Correct answer: Fibrillin-1

The patient's tall stature, long thin face, dislocated lenses, and cardiovascular abnormalities like an enlarged aortic root and mitral valve prolapse are characteristic features of Marfan syndrome. This autosomal dominant disorder results from a mutation in the *FBN1* gene, which encodes fibrillin-1. Fibrillin-1 is a key component of elastic fibers, and its abnormal synthesis leads to weakened connective tissue throughout the body, particularly affecting the skeletal, ocular, and cardiovascular systems.

Question 70: A 45-year-old woman with diabetes presents with a warm, erythematous, tender, well-demarcated area on her left lower leg with a fever of 38.8°C. There is no fluctuance or crepitus. Blood cultures are pending. What is the most likely causative organism?

Staphylococcus aureus and Streptococcus pyogenes (Correct answer)
Pseudomonas aeruginosa
Clostridium perfringens
MRSA exclusively

Correct answer: Staphylococcus aureus and Streptococcus pyogenes

Non-purulent cellulitis is most commonly caused by beta-hemolytic streptococci (especially group A) and Staphylococcus aureus.

Question 71: A 29-year-old Rh-negative woman at 28 weeks has a negative antibody screen and has not previously received Rh immunoglobulin. What is the appropriate management?

Amniocentesis for fetal blood typing before deciding
Obtain Kleihauer-Betke test to guide dosing
Administer Rh immunoglobulin now and again within 72 hours of delivery (Correct answer)
No intervention until delivery unless a sensitizing event occurs

Correct answer: Administer Rh immunoglobulin now and again within 72 hours of delivery

Unsensitized Rh-negative women should receive 300 mcg Rh immunoglobulin at 28 weeks and again postpartum to prevent alloimmunization.

Question 72: An 8-year-old boy is brought to the physician by his mother for a well-child examination. His mother reports that she is exhausted because he is constantly “on the go,” is increasingly difficult to manage, and needs constant supervision. Last week, he climbed out on the roof of their house “just to see how high up it was.” He has had trouble maintaining friendships because he is “bossy” and easily frustrated if he does not win at games. His mother says that he wakes up cheerful and full of energy each morning and that he says he will “really try to be good.” His teacher usually calls by noon to report about his difficult behavior. He is disruptive in class and often “plays the class clown.” When asked to sit still and do his work, he becomes frustrated and shouts, “I can’t sit still.” He is unable to work quietly for more than 15 minutes. The school has threatened to suspend him if his behavior does not improve. His grades are poor. He is at the 70th percentile for height and 45th percentile for weight. Vital signs are within normal limits. Physical examination shows no abnormalities. During the examination, he is cheerful and verbally impulsive. After the examination, his mother becomes tearful and says she does not know what to do. Which of the following is the most appropriate initial response?

“Clearly he needs medication right away.”
“You should look into other schools to give him a fresh start.”
“You should see a therapist to talk about your feelings.”
“It certainly sounds as though things have been difficult for you.” (Correct answer)
“I think that the school is being unfair to your child.”

Correct answer: “It certainly sounds as though things have been difficult for you.”

The mother is clearly distressed and overwhelmed by her son's challenging behaviors, which are consistent with ADHD. The most appropriate initial response from the physician is to validate her feelings and show empathy, acknowledging the difficulty of her situation. This helps establish rapport and trust, which is essential before proceeding with diagnosis, treatment, or further management discussions.

Question 73: A full-term neonate develops jaundice at 18 hours of life. Direct Coombs test is positive. Mother is O-negative; baby is A-positive. Diagnosis?

ABO incompatibility hemolytic disease (Correct answer)
Physiologic jaundice
Rh incompatibility hemolytic disease
Breast milk jaundice

Correct answer: ABO incompatibility hemolytic disease

Early-onset jaundice with a positive Coombs in an O-negative mother with A or B baby indicates ABO hemolytic disease of the newborn.

Question 74: A 25-year-old woman undergoes elective laparoscopic appendectomy for recurrent right lower quadrant pain. The appendix appears grossly normal intraoperatively. The surgeon proceeds with removal. Histopathology reveals a 1.2-cm carcinoid tumor with clear margins. What is the recommended follow-up?

24-hour urine 5-HIAA and octreotide scan
Right hemicolectomy within 4 weeks
Surveillance CT every 6 months for 5 years
No additional workup or surgery is required (Correct answer)

Correct answer: No additional workup or surgery is required

Appendiceal carcinoids less than 2 cm with clear margins are cured by appendectomy alone and require no additional surgery or intensive surveillance.

Question 75: A 42-year-old woman, gravida 2, para 2, comes to the physician because of increasingly frequent loss of urine during the past year. She has loss of urine when she coughs, sneezes, exercises, or plays with her children. Her incontinence is never preceded by a sudden urge to void, and she does not have loss of urine at night. Her children were born after uncomplicated vaginal deliveries. She has no history of other hospital admissions or serious illness. She takes no medications. Abdominal examination shows no abnormalities. The external genitalia, vagina, and cervix appear normal. The uterus and adnexa are normal to palpation. There is loss of a small amount of urine with Valsalva maneuver. Her postvoid residual volume is 50 mL. Urinalysis shows no abnormalities. Which of the following is the most likely diagnosis?

Vesicovaginal fistula
Urinary tract infection
Overactive bladder with incontinence
Overflow incontinence
Stress incontinence (Correct answer)

Correct answer: Stress incontinence

The patient's symptoms of involuntary urine leakage with activities that increase intra-abdominal pressure (coughing, sneezing, exercise) and the absence of urgency or nocturnal incontinence are classic for stress incontinence. The finding of urine loss with a Valsalva maneuver and a normal postvoid residual volume further supports this diagnosis, indicating urethral hypermobility or intrinsic sphincter deficiency.

Question 76: The committed and rate-limiting step of de novo fatty acid synthesis is catalyzed by which enzyme?

Malonyl-CoA decarboxylase
Fatty acid synthase
ATP-citrate lyase
Acetyl-CoA carboxylase (Correct answer)

Correct answer: Acetyl-CoA carboxylase

Acetyl-CoA carboxylase (requiring biotin) converts acetyl-CoA to malonyl-CoA, the committed, rate-limiting step of fatty acid synthesis.

Question 77: A 30-year-old man with a bee allergy is stung and develops urticaria, wheezing, hypotension (BP 78/50), and stridor within minutes. What is the immediate treatment of choice?

Methylprednisolone IV
Epinephrine 0.3 mg IM into the anterolateral thigh (Correct answer)
Diphenhydramine IV
Albuterol nebulizer

Correct answer: Epinephrine 0.3 mg IM into the anterolateral thigh

Intramuscular epinephrine to the anterolateral thigh is the first and most critical treatment for anaphylaxis, reversing bronchospasm, hypotension, and angioedema.

Question 78: A previously healthy 16-year-old girl is brought to the physician because of abdominal cramps, bloating, and loose stools for 6 months. These symptoms began after she ingested skim milk in an attempt to lose weight. She is at the 50th percentile for height and 75th percentile for weight. Physical examination shows no abnormalities. Stool studies show a 3+ Clinitest reagent response and pH of 5. After the patient ingests milk, there is an increased hydrogen concentration in expired air. A deficiency of which of the following enzyme activities is the most likely cause of the gastrointestinal symptoms in this patient?

Amylase
Carboxypeptidase
Galactokinase
Lactase (Correct answer)
Fructose-1,6-bisphosphate aldolase
Sucrase

Correct answer: Lactase

The patient's symptoms (abdominal cramps, bloating, loose stools) after consuming milk, along with a positive stool Clinitest, acidic stool pH, and increased expired hydrogen, are classic signs of lactose intolerance. This condition results from a deficiency in lactase, the enzyme responsible for breaking down lactose (milk sugar) into glucose and galactose in the small intestine. Undigested lactose ferments in the colon, producing gas and acidic byproducts.

Question 79: A 50-year-old man comes to the physician because of progressive fatigue and darkening of his skin during the past 2 years. He has not spent much time in the sun during this period. Physical examination shows slate-gray skin and hepatomegaly. Serum studies show: Ferritin 500 ng/mL Transferrin saturation 70% (N=20%–60%) AST 41 U/L ALT 45 U/L A liver biopsy specimen stained with Prussian blue is positive. Which of the following best describes the altered function of mutated HFE gene product in this patient?

Increased iron absorption (Correct answer)
Decreased oxidase activity
Increased fatty acid absorption
Decreased NADPH production
Decreased lysozyme synthesis

Correct answer: Increased iron absorption

The patient's symptoms of fatigue, skin darkening, hepatomegaly, elevated ferritin, and high transferrin saturation, along with positive Prussian blue staining on liver biopsy (indicating iron deposition), are classic for hemochromatosis. This condition is most commonly caused by a mutation in the HFE gene, which leads to inappropriately increased iron absorption from the gastrointestinal tract, resulting in systemic iron overload and organ damage.

Question 80: An 8-month-old girl is brought to the emergency department because of a 1-day history of rapid breathing. Her temperature is 38.4°C (101.1°F), pulse is 160/min, respirations are 60/min, and blood pressure is 100/68 mm Hg. Bilateral expiratory wheezing and crackles are heard on auscultation. A chest x-ray shows areas of atelectasis and hyperinflation. Which of the following is the most likely causal virus?

Rhinovirus
Respiratory syncytial virus (Correct answer)
Measles virus
Varicella-zoster virus

Correct answer: Respiratory syncytial virus

The clinical picture of an 8-month-old infant with rapid breathing, fever, bilateral expiratory wheezing and crackles, and chest x-ray findings of atelectasis and hyperinflation is highly characteristic of bronchiolitis. Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants and young children. RSV infection leads to inflammation and obstruction of the small airways, resulting in the observed respiratory distress and lung findings.

Question 81: Stimulation of which receptor type by norepinephrine results in mydriasis (pupil dilation)?

Muscarinic M3 receptors on the sphincter pupillae
Alpha-1 adrenergic receptors on the dilator pupillae (Correct answer)
Nicotinic receptors on the superior cervical ganglion
Beta-2 adrenergic receptors on the ciliary muscle

Correct answer: Alpha-1 adrenergic receptors on the dilator pupillae

Sympathetic norepinephrine activates α1-adrenergic receptors on the radial dilator pupillae muscle, causing contraction and mydriasis; loss of sympathetic tone (Horner's) causes miosis.

Question 82: Aldosterone's primary effect on the collecting duct principal cells is:

Increasing Na+ reabsorption and K+ secretion (Correct answer)
Decreasing Na+/K+-ATPase activity
Increasing aquaporin-2 insertion
Inhibiting ENaC channels

Correct answer: Increasing Na+ reabsorption and K+ secretion

Aldosterone upregulates apical ENaC and basolateral Na+/K+-ATPase, promoting sodium retention and potassium excretion.

Question 83: Three weeks after traveling to California to study desert flowers, a 33-year-old man develops fever, chest pain, and muscle soreness. Two days later, red, tender nodules appear on the shins, and the right ankle is tender and painful. An x-ray of the chest shows a left pleural effusion. Which of the following is the most likely diagnosis?

Coccidioidomycosis (Correct answer)
Blastomycosis
Mycoplasma pneumoniae infection
Mycobacterium marinum infection
Histoplasmosis

Correct answer: Coccidioidomycosis

The patient's travel history to California, an endemic region for Coccidioides immitis, combined with symptoms of fever, chest pain, muscle soreness, and the characteristic skin lesions of erythema nodosum (red, tender nodules on the shins), strongly points to coccidioidomycosis. This fungal infection, also known as 'desert fever,' often presents with respiratory symptoms and extrapulmonary manifestations like arthralgias and erythema nodosum, consistent with the patient's findings.

Question 84: A 45-year-old woman reports fatigue, cold intolerance, constipation, and weight gain over 6 months. TSH is 18 mIU/L and free T4 is low. Which finding would most specifically indicate an autoimmune cause?

Elevated TSH
Positive anti-TPO antibodies (Correct answer)
Low free T4
Diffuse goiter on ultrasound

Correct answer: Positive anti-TPO antibodies

Positive anti-thyroid peroxidase (anti-TPO) antibodies are the hallmark of Hashimoto thyroiditis, the most common autoimmune cause of hypothyroidism.

Question 85: A 3799-g (8-lb 6-oz) female newborn is born by cesarean delivery because of a breech presentation. Apgar scores are 7 and 9 at 1 and 5 minutes, respectively. Initial examination shows a palpable clunk when the left hip is abducted, flexed, and lifted forward. Posterior pressure on the flexed hip elicits a similar clunk. The remainder of the examination shows no abnormalities. Which of the following is the most likely diagnosis?

Congenital hip dysplasia (Correct answer)
Legg-Calvé-Perthes disease
Osteogenesis imperfecta
Osgood-Schlatter disease
Slipped capital femoral epiphysis

Correct answer: Congenital hip dysplasia

The description of a palpable 'clunk' during specific maneuvers (Ortolani and Barlow tests) is pathognomonic for developmental dysplasia of the hip (DDH), also known as congenital hip dysplasia. The Ortolani maneuver reduces a dislocated hip, while the Barlow maneuver dislocates an unstable hip. Breech presentation is a known risk factor for this condition.

Question 86: An 18-year-old woman comes to the physician because of nausea, vomiting, and abdominal pain 1 hour after ingesting a glass of wine with dinner. Three days ago, she began antibiotic treatment for vaginitis after a wet mount preparation of vaginal discharge showed a motile protozoan. This patient most likely has been taking which of the following drugs?

Clindamycin
Metronidazole (Correct answer)
Chloroquine
Ceftriaxone

Correct answer: Metronidazole

The patient's symptoms of nausea, vomiting, and abdominal pain after consuming wine while on an antibiotic for a motile protozoan (likely metronidazole for Trichomonas vaginitis) are characteristic of a disulfiram-like reaction. Metronidazole inhibits aldehyde dehydrogenase, an enzyme crucial for alcohol metabolism. This inhibition leads to an accumulation of acetaldehyde, causing unpleasant symptoms like flushing, nausea, and vomiting.

Question 87: A 55-year-old postmenopausal woman presents with vaginal bleeding. Endometrial biopsy shows complex atypical hyperplasia. What is the recommended next step?

Repeat biopsy in 3 months
Total hysterectomy (Correct answer)
Cyclic progestin therapy for 6 months
External beam radiation therapy

Correct answer: Total hysterectomy

Complex atypical hyperplasia carries a 25–30% risk of concurrent endometrial carcinoma, so total hysterectomy is the definitive treatment.

Question 88: A 45-year-old man has acute low back and left leg pain radiating to the lateral foot. He has weakness in left ankle dorsiflexion and reduced sensation on the dorsum of the foot. Which nerve root is compressed?

L4
L5 (Correct answer)
L3
S1

Correct answer: L5

L5 radiculopathy presents with weakness of ankle dorsiflexion and toe extension, and sensory loss over the dorsum of the foot and lateral lower leg.

Question 89: A 30-year-old man has had nausea, vomiting, and severe colicky right flank pain radiating into the thigh for 4 hours. He is afebrile. There is right costovertebral angle tenderness. Urinalysis shows RBCs too numerous to count and no bacteria. Which of the following is the most likely diagnosis?

Benign prostatic hyperplasia
Urinary tract tuberculosis
Bladder carcinoma
Acute glomerulonephritis
Renal cell carcinoma
Bacterial cystitis
Urolithiasis (Correct answer)

Correct answer: Urolithiasis

The patient's presentation of sudden-onset, severe, colicky right flank pain radiating into the thigh, accompanied by right costovertebral angle tenderness and hematuria (RBCs in urine) without signs of infection (afebrile, no bacteria), is classic for urolithiasis (kidney stones). The pain is caused by the obstruction of the ureter by the stone, leading to distension and spasm.

Question 90: A 70-year-old woman has a complete small bowel obstruction confirmed on CT. She has no peritoneal signs, no fever, and WBC is 9,000/μL. What is the initial management?

NGT decompression, IV fluids, and serial abdominal exams (Correct answer)
Colonoscopic decompression
High-dose IV corticosteroids
Immediate exploratory laparotomy

Correct answer: NGT decompression, IV fluids, and serial abdominal exams

A complete SBO without signs of strangulation or peritonitis is initially managed non-operatively with NGT decompression and fluid resuscitation.

Question 91: A patient presents with deviation of the uvula to the right, hoarseness, and dysphagia after a posterior inferior cerebellar artery stroke. Which nerve is most directly affected at the level of the medulla?

CN X (vagus) (Correct answer)
CN IX only
CN VII
CN XII

Correct answer: CN X (vagus)

Lateral medullary (Wallenberg) syndrome affects CN X nuclei, causing ipsilateral palatal and vocal cord paralysis with uvular deviation away from the lesion.

Question 92: A 4-year-old presents with a barking cough and inspiratory stridor. The causative virus replicates in respiratory epithelium and has a negative-sense, single-stranded RNA genome with a helical nucleocapsid. Which virus family does this pathogen belong to?

Coronaviridae
Picornaviridae
Orthomyxoviridae
Paramyxoviridae (Correct answer)

Correct answer: Paramyxoviridae

Parainfluenza virus, the most common cause of croup (laryngotracheobronchitis), belongs to Paramyxoviridae and has a negative-sense ssRNA genome with helical symmetry.

Question 93: A 3-year-old child presents with fever, neck stiffness, and petechial rash. CSF shows glucose 30 mg/dL (serum 90), protein 180 mg/dL, WBC 1,200 (90% PMN). What organism is most likely?

Neisseria meningitidis (Correct answer)
Listeria monocytogenes
Haemophilus influenzae
Streptococcus pneumoniae

Correct answer: Neisseria meningitidis

N. meningitidis classically causes bacterial meningitis with petechial/purpuric rash in children and young adults and is the most common cause of epidemic meningitis.

Question 94: A 25-year-old woman with 6 weeks of amenorrhea presents with right lower quadrant pain and a positive urine pregnancy test. Pelvic ultrasound shows no intrauterine pregnancy and a 2.5 cm right adnexal mass. What is the diagnosis?

Ectopic pregnancy (Correct answer)
Ruptured ovarian cyst
Ovarian torsion
Acute appendicitis

Correct answer: Ectopic pregnancy

A positive beta-hCG with no intrauterine pregnancy on ultrasound and an adnexal mass is an ectopic pregnancy until proven otherwise.

Question 95: Which of the following is a major metabolic effect of cortisol?

Inhibits lipolysis in adipose tissue
Increases gluconeogenesis in the liver (Correct answer)
Promotes protein synthesis in skeletal muscle
Decreases blood glucose by promoting glycogen synthesis

Correct answer: Increases gluconeogenesis in the liver

Cortisol stimulates hepatic gluconeogenesis, promotes muscle protein catabolism, and enhances lipolysis, all serving to raise blood glucose during stress.

Question 96: A 14-year-old girl refuses to attend school, claiming stomach pain every morning. Medical workup is negative. She stays home and plays video games when not in school. What is the most likely diagnosis?

Somatic symptom disorder
School avoidance (separation anxiety or social anxiety) (Correct answer)
Illness anxiety disorder
Factitious disorder imposed on self

Correct answer: School avoidance (separation anxiety or social anxiety)

School avoidance with somatic complaints and secondary gain (staying home) is most consistent with anxiety-driven school refusal, often linked to separation or social anxiety.

Question 97: A 30-year-old man comes to the emergency department 1 hour after injuring his left knee in a volleyball game. He says he twisted his left leg when he fell to the floor after he and a teammate accidentally collided. He cannot bear weight on his left leg. Physical examination shows tenderness and swelling of the left knee. When the patient sits on the edge of the examination table, the left knee can be displaced anteriorly at an abnormal degree. Which of the following is most likely injured in this patient?

Oblique popliteal ligament
Fibular collateral ligament
Anterior cruciate ligament (Correct answer)
Transverse ligament of the knee
Meniscofemoral ligament

Correct answer: Anterior cruciate ligament

The anterior displacement of the tibia relative to the femur (implied by the knee being displaced anteriorly at an abnormal degree) is the classic sign of an anterior cruciate ligament (ACL) injury. The ACL prevents anterior translation of the tibia on the femur and hyperextension of the knee, and its rupture often occurs with twisting injuries during sports.

Question 98: Elastic arteries (e.g., the aorta) differ from muscular arteries primarily by having a tunica media dominated by which component?

Smooth muscle cells
Endothelial cells
Dense irregular collagen
Elastic lamellae (Correct answer)

Correct answer: Elastic lamellae

The aortic media contains numerous concentric elastic lamellae that store systolic energy and maintain diastolic pressure via the Windkessel effect.

Question 99: Antipsychotic drugs block D2 receptors in the nigrostriatal pathway. This blockade leads to which adverse effect?

Reduced positive symptoms via mesolimbic pathway blockade
Improved working memory via mesocortical pathway enhancement
Hyperprolactinemia due to tuberoinfundibular pathway blockade
Extrapyramidal symptoms (EPS) such as parkinsonism and tardive dyskinesia (Correct answer)

Correct answer: Extrapyramidal symptoms (EPS) such as parkinsonism and tardive dyskinesia

D2 blockade in the nigrostriatal pathway causes extrapyramidal side effects including acute dystonia, akathisia, parkinsonism (early), and tardive dyskinesia (late with chronic use).

Question 100: A researcher concludes there is no difference in blood pressure reduction between two drugs when in fact one drug is superior. This error is classified as:

Selection bias
Type I error (alpha error)
Type II error (beta error) (Correct answer)
Confounding

Correct answer: Type II error (beta error)

A Type II (beta) error is a false-negative: failing to detect a real difference that truly exists.

Question 101: A previously healthy 18-year-old woman is brought to the physician for evaluation because of loss of appetite, sleeplessness, and extreme irritability for 3 weeks. After missing many practices, she quit the college softball team that she previously enjoyed. She often feels tired and has difficulty sitting still and concentrating on schoolwork. Her menses occur at regular intervals. She weighs 50 kg (110 lb) and is 168 cm (5 ft 6 in) tall; her BMI is 18 kg/m2 . Her pulse is 74/min, respirations are 16/min, and blood pressure is 110/70 mm Hg. Which of the following is the most likely diagnosis?

Major depressive disorder
Attention-deficit/hyperactivity disorder
Anorexia nervosa
Dysthymic disorder
Adjustment disorder with mixed disturbance of emotions and conduct (Correct answer)

Correct answer: Adjustment disorder with mixed disturbance of emotions and conduct

This patient presents with a constellation of emotional (irritability, sleeplessness) and behavioral (quitting softball, difficulty concentrating, restlessness) symptoms that developed within 3 weeks, following a clear stressor (quitting the softball team, likely related to academic pressure). These symptoms cause significant distress and functional impairment but do not meet the full criteria for a major depressive episode or an eating disorder like anorexia nervosa, making adjustment disorder with mixed disturbance of emotions and conduct the most fitting diagnosis.

Question 102: A child with severe combined immunodeficiency (SCID) is found to have adenosine deaminase (ADA) deficiency. Toxic accumulation of which compound destroys lymphocytes?

PRPP
Deoxyadenosine triphosphate (dATP) (Correct answer)
Hypoxanthine and xanthine
Orotic acid

Correct answer: Deoxyadenosine triphosphate (dATP)

ADA deficiency causes deoxyadenosine accumulation, which is phosphorylated to dATP; excess dATP inhibits ribonucleotide reductase and induces apoptosis in lymphocytes.

Question 103: A patient on warfarin presents with INR of 8 and active bleeding. Which agent provides the most rapid reversal of warfarin anticoagulation?

Vitamin K (oral)
Protamine sulfate
Fresh frozen plasma (Correct answer)
Tranexamic acid

Correct answer: Fresh frozen plasma

Fresh frozen plasma provides immediate replenishment of all clotting factors and is the fastest reversal for life-threatening warfarin-related bleeding.

Question 104: A 36-year-old woman with hypertension well-controlled on lisinopril asks about contraception. Which method is CONTRAINDICATED in this patient?

Copper intrauterine device
Progestin-only pills (mini-pill)
Levonorgestrel-releasing IUD
Combined estrogen-progestin oral contraceptives (Correct answer)

Correct answer: Combined estrogen-progestin oral contraceptives

Combined oral contraceptives are contraindicated in women with hypertension due to increased risk of stroke and myocardial infarction, especially over age 35.

Question 105: A 35-year-old soldier returning from combat has nightmares, flashbacks, avoidance of crowds, and hypervigilance for 3 months after witnessing deaths of fellow soldiers. What is the diagnosis?

Acute stress disorder
Adjustment disorder with anxiety
Post-traumatic stress disorder (Correct answer)
Generalized anxiety disorder

Correct answer: Post-traumatic stress disorder

PTSD is diagnosed when intrusion, avoidance, negative cognitions/mood, and hyperarousal symptoms persist for more than 1 month after a traumatic event.

Question 106: A 16-year-old girl is brought to the physician because of severe acne over her face and upper back for 6 months. She has had no itching or scaling of the acne. Treatment with topical and oral antibiotics has not resolved her symptoms. Examination shows numerous papules and pustules with widespread erythema over the face and upper back. There is no hyperpigmentation. The patient requests information about beginning isotretinoin, because she says it improved her boyfriend’s acne. Which of the following is the most appropriate initial step prior to treatment with isotretinoin?

Complete blood count with differential
24-Hour urine collection for measurement of creatinine clearance
Measurement of urine β-hCG concentration (Correct answer)
PPD skin test
Measurement of serum thyroid-stimulating hormone concentration
Determination of prothrombin and partial thromboplastin times

Correct answer: Measurement of urine β-hCG concentration

Isotretinoin is a highly effective treatment for severe acne but is a potent teratogen, meaning it causes severe birth defects. Therefore, it is absolutely contraindicated in pregnancy. Before initiating isotretinoin in any female of childbearing potential, a pregnancy test, such as a urine β-hCG concentration measurement, is mandatory to ensure the patient is not pregnant, along with strict contraception counseling.

Question 107: A 65-year-old woman has lancinating electric shock-like pain in her cheek triggered by chewing and light touch. Neurological exam is normal. MRI shows vascular compression of a cranial nerve root. What is the diagnosis?

Cluster headache
Post-herpetic neuralgia
Trigeminal neuralgia (Correct answer)
Glossopharyngeal neuralgia

Correct answer: Trigeminal neuralgia

Trigeminal neuralgia presents with brief, severe, unilateral facial pain in V2/V3 distribution triggered by light touch or chewing, often caused by vascular loop compression of CN V.

Question 108: A 48-year-old man undergoes laparoscopic cholecystectomy. On post-op day 2 he develops RUQ pain, fever, and elevated liver enzymes. Repeat ultrasound shows a fluid collection near the liver. MRCP reveals a bile duct injury with bile leak. What is the initial management?

Oral antibiotics and observation
Immediate surgical re-exploration and repair
Percutaneous drainage of collection only
ERCP with biliary stenting (Correct answer)

Correct answer: ERCP with biliary stenting

Post-cholecystectomy bile leak from a minor duct injury is initially managed with ERCP and biliary stenting to reduce ductal pressure and allow healing.

Question 109: A 3-year-old with Down syndrome is found to have an atrioventricular septal defect. Which chromosomal location is the TRISOMY associated with?

Chromosome 21 (Correct answer)
Chromosome 18
Chromosome 13
Chromosome 22

Correct answer: Chromosome 21

Down syndrome results from trisomy 21 and is strongly associated with AVSD (endocardial cushion defect).

Question 110: A 34-year-old woman with major depressive disorder comes to the physician for a follow-up examination. She says that her depressive symptoms are worsening. Multiple medication regimens have been ineffective. The patient says that she spoke recently with a former college roommate who also has depression. Her friend is currently enrolled in a clinical trial for a new antidepressant at a local center. The patient says, “My friend seems to be doing really well with this new medication, and I think I’d like to try it out to see if it would work for me, too. Can you write me a referral to the center where my friend is enrolled?” Which of the following is the most appropriate initial response by the physician to this patient’s request?

Discuss the conduct of clinical trials so that the patient has a clear understanding of how they operate (Correct answer)
Inform the patient that she cannot receive future care from the physician if she enrolls in the clinical trial
Refer the patient to the center because so many other treatment options have failed
Decline to refer the patient because she has treatment-refractory depression that typically is not accepted into clinical trials
Inform the patient that she will not get the best care possible if she enrolls in an experimental trial

Correct answer: Discuss the conduct of clinical trials so that the patient has a clear understanding of how they operate

Before referring a patient to a clinical trial, it is essential to ensure they have a realistic understanding of what participation entails. This includes explaining concepts like randomization, placebo arms, potential for unknown side effects, and the research nature of the treatment, rather than just assuming it's a guaranteed cure. This empowers the patient to make an informed decision.

Question 111: A 72-year-old man with hypertension presents with palpitations. ECG shows irregularly irregular rhythm with absent P waves. He has no prior anticoagulation history. CHA2DS2-VASc score is 3. What is the most appropriate management for stroke prevention?

Aspirin 81 mg daily
No anticoagulation needed
Warfarin with target INR 2–3
Direct oral anticoagulant (e.g., apixaban) (Correct answer)

Correct answer: Direct oral anticoagulant (e.g., apixaban)

A CHA2DS2-VASc score ≥2 in men with atrial fibrillation warrants anticoagulation; DOACs are preferred over warfarin for non-valvular AF due to better efficacy and safety profile.

NBME Clinical Science Subject Examination (Shelf Exam)

The NBME Shelf Exams are standardized subject exams administered at the end of core clinical clerkships in medical school. Each exam contains 110 multiple-choice questions to be completed in 165 minutes, assessing clinical knowledge across disciplines such as medicine, surgery, pediatrics, psychiatry, and obstetrics/gynecology.

110

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165 min

Time Limit

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