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

Question 1: A 52-year-old man has painless progressive weakness in his right hand with fasciculations, hyperreflexia, and an extensor plantar response. Tongue fasciculations are noted. What diagnosis fits?

Amyotrophic lateral sclerosis (Correct answer)
Multiple sclerosis
Kennedy disease
Myasthenia gravis

Correct answer: Amyotrophic lateral sclerosis

ALS involves both upper (hyperreflexia, extensor plantar) and lower (fasciculations, atrophy) motor neuron signs across multiple body regions with bulbar involvement.

Question 2: A 32-year-old G1P0 at 34 weeks develops sudden severe abdominal pain, a board-like rigid uterus, and fetal bradycardia. What is the most likely diagnosis?

Uterine rupture
Complete placenta previa
Placental abruption (Correct answer)
Acute polyhydramnios

Correct answer: Placental abruption

Sudden severe pain with uterine rigidity and fetal distress is the classic presentation of placental abruption (premature separation of the placenta).

Question 3: 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 B6 (pyridoxine)
Folic acid (Correct answer)
Vitamin B1 (thiamine)
Vitamin B12 (cyanocobalamin)
Vitamin B2 (riboflavin)
Biotin

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 4: A 36-year-old woman comes to the physician because of a 10-month history of difficulty falling asleep due to a crawling sensation in her legs. She has to get up several times during the night to relieve the feeling. The symptoms started shortly after she delivered her son 1 year ago. She says her husband complains because she has become a “jumpy” sleeper, and her movements sometimes wake him up. Physical examination shows no abnormalities. Which of the following is the most likely diagnosis?

Sleep myoclonus
Amyotrophic lateral sclerosis
Restless legs syndrome (Correct answer)
Multiple sclerosis
REM sleep behavior disorder

Correct answer: Restless legs syndrome

The patient's symptoms—an irresistible urge to move the legs, often with uncomfortable 'crawling' sensations, worse at rest/night, and relieved by movement—are the cardinal features of Restless Legs Syndrome (RLS). The onset during pregnancy/postpartum is common, and the 'jumpy' sleep likely refers to periodic limb movements in sleep (PLMS), which frequently co-occur with RLS. Other conditions like ALS or MS do not present with this specific constellation of sensory discomfort and urge to move.

Question 5: A 47-year-old man comes to the physician because of a 2-year history of fatigue. He has had progressive difficulty with daytime sleepiness and has intermittently fallen asleep at work. He has no difficulty falling asleep or staying asleep at night but awakens in the morning not feeling well rested. His vital signs are within normal limits. Examination of the throat shows no abnormalities except for hypertrophied tonsils. His hemoglobin concentration is 17.9 g/dL, leukocyte count is 8700/mm3 , and platelet count is 170,000/mm3 . Which of the following is the most likely cause of this patient’s symptoms?

Polycythemia vera
Erythroleukemia
Chronic fatigue syndrome
Sleep apnea (Correct answer)
Chronic Epstein-Barr virus infection

Correct answer: Sleep apnea

The patient's chronic fatigue, excessive daytime sleepiness despite adequate sleep duration, and unrefreshing sleep are classic symptoms of sleep apnea. Hypertrophied tonsils are a common anatomical factor contributing to airway obstruction. The elevated hemoglobin concentration (polycythemia) is a significant clue, as chronic nocturnal hypoxemia due to sleep apnea stimulates erythropoietin production, leading to secondary polycythemia.

Question 6: A 3175-g (7-lb) newborn is delivered at term to a 21-year-old woman, gravida 1, para 1. Pregnancy, labor, and delivery were uncomplicated. Examination shows ambiguous genitalia. Which of the following is the most appropriate physician response to the parents regarding their newborn’s gender?

“Your baby is a boy, but his genitals are not yet fully developed.”
“The decision about your child’s gender is entirely yours.”
“Your baby looks healthy, but we will not know the gender until we run additional tests.” (Correct answer)
“You have a beautiful new daughter.”

Correct answer: “Your baby looks healthy, but we will not know the gender until we run additional tests.”

When a newborn presents with ambiguous genitalia, it is crucial for the physician to avoid assigning a gender prematurely, as this can have significant psychological and social consequences if incorrect. The most appropriate response is to acknowledge the baby's health while explaining that additional tests are necessary to determine the genetic and biological sex, allowing for an informed decision about gender assignment.

Question 7: A 19-year-old woman comes to the physician because of a 3-month history of intermittent drooping of her left eyelid each evening and occasional difficulty chewing and swallowing. She also has had two episodes of double vision that occurred in the evening and resolved by the following morning. Examination shows no abnormalities except for slight ptosis on the right. Which of the following is the most likely diagnosis?

Acute intermittent porphyria
Myasthenia gravis (Correct answer)
Complex partial seizures
Guillain-Barré syndrome
Brain stem glioma

Correct answer: Myasthenia gravis

The patient's fluctuating symptoms of ptosis, diplopia, and difficulty chewing/swallowing, which worsen with activity or at the end of the day and improve with rest, are highly characteristic of myasthenia gravis. This autoimmune disorder involves antibodies attacking acetylcholine receptors at the neuromuscular junction, leading to fatigable muscle weakness, particularly affecting ocular and bulbar muscles.

Question 8: 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 9: A 28-year-old woman with primary infertility undergoes hysterosalpingography showing bilateral tubal occlusion. Her partner's semen analysis is normal. What is the most likely cause of her tubal pathology?

Congenital Müllerian duct anomaly
Endometriosis with peritubal adhesions
Prior Chlamydia trachomatis pelvic infection (Correct answer)
Asherman syndrome from prior D&C

Correct answer: Prior Chlamydia trachomatis pelvic infection

Prior Chlamydia trachomatis infection causing pelvic inflammatory disease is the most common cause of tubal factor infertility due to tubal scarring and occlusion.

Question 10: A 66-year-old man with known cirrhosis presents with massive upper GI bleeding. Upper endoscopy reveals actively bleeding esophageal varices. After band ligation, bleeding is controlled. What medication should be started to reduce rebleeding risk?

Omeprazole
Propranolol (Correct answer)
Lactulose
Spironolactone

Correct answer: Propranolol

Non-selective beta-blockers such as propranolol reduce portal pressure and are the mainstay of secondary prophylaxis against variceal rebleeding.

Question 11: A 55-year-old man with diabetes and hypertension is found to have creatinine of 3.8 mg/dL (baseline 1.1 mg/dL) after starting an NSAID 5 days ago. Urinalysis shows muddy brown casts. What is the most likely mechanism of injury?

Prerenal azotemia from volume depletion
Acute interstitial nephritis
Acute tubular necrosis (Correct answer)
Post-renal obstruction

Correct answer: Acute tubular necrosis

Muddy brown granular casts are pathognomonic of acute tubular necrosis, which can be caused by NSAIDs reducing renal perfusion in patients with marginal renal blood flow.

Question 12: A 55-year-old man develops acute low back pain, perianal saddle anesthesia, bilateral leg weakness, and urinary retention after lifting. What is the most urgent next step?

IV steroids and observation
Oral NSAIDs and bed rest
Lumbar puncture
Emergent MRI lumbar spine and surgical consultation (Correct answer)

Correct answer: Emergent MRI lumbar spine and surgical consultation

Cauda equina syndrome (saddle anesthesia, bowel/bladder dysfunction, bilateral leg weakness) is a surgical emergency requiring emergent MRI and decompression within hours to preserve function.

Question 13: 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
Albuterol nebulizer
Diphenhydramine IV
Epinephrine 0.3 mg IM into the anterolateral thigh (Correct answer)

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 14: During normal screening for phenylketonuria, a male newborn has a serum phenylalanine concentration of 35 mg/dL (greater than 20 mg/dL is considered a positive test). Signs of tyrosine deficiency also are apparent. Enzymatic analysis using cultured fibroblasts, obtained after circumcision, shows normal activity of phenylalanine hydroxylase. A possible explanation for these findings is a deficiency in function of which of the following coenzymes?

Biopterin (Correct answer)
Adenosylcobalamin
Tetrahydrofolic acid
Dihydroquinone
Pyridoxal phosphate

Correct answer: Biopterin

While classical phenylketonuria (PKU) is caused by a deficiency in phenylalanine hydroxylase (PAH), this patient has normal PAH activity. Therefore, the hyperphenylalaninemia and tyrosine deficiency are most likely due to a defect in tetrahydrobiopterin (BH4) metabolism. BH4 is an essential cofactor for phenylalanine hydroxylase, and its deficiency prevents the conversion of phenylalanine to tyrosine, leading to a form of atypical PKU.

Question 15: 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?

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

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 16: A 22-year-old woman with a 10-year history of asthma comes to the physician because she has had to increase her use of her albuterol inhaler during the past 6 weeks. Her asthma was previously well controlled with inhaled glucocorticoids. She has a 2-year history of generalized anxiety disorder controlled with fluoxetine and a 5-year history of migraines. The migraines were well controlled with sumatriptan until 4 months ago when she began to have headaches twice weekly; propranolol was added to her regimen at that time. She has been taking an oral contraceptive for the past year. She says she has been under increased stress at graduate school and in her personal life during the past 3 months; during this period, she has been drinking an average of four cups of coffee daily (compared with her usual one cup daily). She does not drink alcohol or use illicit drugs. She appears mildly anxious but is not in respiratory distress. Scattered end-expiratory wheezes are heard. The remainder of the examination shows no abnormalities. Which of the following is the most likely cause of the exacerbation of this patient’s asthma?

Increased caffeine intake
Propranolol therapy (Correct answer)
Sumatriptan therapy
Fluoxetine therapy
Oral contraceptive therapy

Correct answer: Propranolol therapy

Propranolol is a non-selective beta-blocker, meaning it blocks both beta-1 and beta-2 adrenergic receptors. Beta-2 receptors are abundant in the bronchial smooth muscle, and their blockade by propranolol can lead to bronchoconstriction. This effect directly counteracts the bronchodilatory action of albuterol and can significantly exacerbate asthma symptoms, making it a contraindicated medication for most asthmatic patients.

Question 17: 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?

Active efflux of the antibiotic from the bacteria
Production of β-lactamase by the bacteria (Correct answer)
Mutation of the 30S ribosomal subunit
Mutation of the 50S ribosomal subunit
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 18: A patient with temporal lobe epilepsy most likely presents with which type of seizure?

Complex partial seizures with automatisms and postictal confusion (Correct answer)
Myoclonic jerks in the morning
Tonic-clonic seizures without aura
Absence seizures with 3-Hz spike-and-wave on EEG

Correct answer: Complex partial seizures with automatisms and postictal confusion

Temporal lobe (mesial) epilepsy classically produces complex partial seizures with an aura (often déjà vu or epigastric rising), automatisms (lip smacking, picking), and postictal confusion.

Question 19: A 10-month-old male has recurrent bacterial infections including pneumonia and otitis media since 6 months of age. Serum immunoglobulins are markedly low. B-cell count is undetectable. Most likely diagnosis?

SCID
Hyper-IgM syndrome
X-linked agammaglobulinemia (Bruton) (Correct answer)
Selective IgA deficiency

Correct answer: X-linked agammaglobulinemia (Bruton)

X-linked agammaglobulinemia (Bruton) presents with absent B cells and profound hypogammaglobulinemia, causing recurrent bacterial infections after maternal antibody wanes at 6 months.

Question 20: Which is the rate-limiting enzyme of cholesterol biosynthesis and the target of statin drugs?

Lanosterol synthase
HMG-CoA synthase
Squalene 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 21: A 30-year-old woman presents with recurrent DVTs, spontaneous abortions, and a positive lupus anticoagulant test. Which pathological mechanism underlies her condition?

Complement-mediated endothelial injury
Factor V Leiden mutation
Protein C deficiency
Autoantibodies against phospholipid-binding proteins (Correct answer)

Correct answer: Autoantibodies against phospholipid-binding proteins

Antiphospholipid syndrome is caused by autoantibodies (anti-beta2-glycoprotein I, anticardiolipin) that promote thrombosis and pregnancy loss.

Question 22: 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?

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

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 23: A surgeon needs to provide postoperative analgesia while minimizing opioid use. Which mechanism do NSAIDs use to reduce pain and inflammation?

Block sodium channels in sensory neurons
Inhibit cyclooxygenase, reducing prostaglandin synthesis (Correct answer)
Activate GABA-A receptors in the spinal cord
Block histamine H1 receptors peripherally

Correct answer: Inhibit cyclooxygenase, reducing prostaglandin synthesis

NSAIDs inhibit COX-1 and COX-2 enzymes, preventing arachidonic acid conversion to prostaglandins that sensitize pain receptors and mediate inflammation.

Question 24: A neonate born to a mother with poorly controlled diabetes develops jitteriness, hypotonia, and poor feeding at 2 hours of life. Blood glucose is 28 mg/dL. First step?

Observe and recheck in 1 hour
IV D10W bolus (Correct answer)
IM glucagon
Oral formula feeding

Correct answer: IV D10W bolus

Symptomatic neonatal hypoglycemia requires immediate IV dextrose bolus (D10W 2 mL/kg) to rapidly restore euglycemia.

Question 25: Which of the following muscle cell components helps spread the depolarization of the muscle cell membranes throughout the interior of muscle cells?

Troponin
T tubule (Correct answer)
Myosin
Tropomyosin
Z disk
Actin

Correct answer: T tubule

T-tubules (transverse tubules) are invaginations of the muscle cell membrane (sarcolemma) that penetrate deep into the muscle fiber. Their primary function is to rapidly transmit the action potential (depolarization) from the sarcolemma to the interior of the muscle cell, ensuring that all myofibrils contract simultaneously. This allows for efficient and coordinated muscle contraction.

Question 26: A 28-year-old woman presents with bloody diarrhea, tenesmus, and crampy abdominal pain for 3 weeks. Colonoscopy shows continuous mucosal inflammation from the rectum to the splenic flexure. Which feature best distinguishes this condition from Crohn disease?

Transmural inflammation
Presence of granulomas on biopsy
Continuous colonic involvement starting at the rectum (Correct answer)
Involvement of the terminal ileum

Correct answer: Continuous colonic involvement starting at the rectum

Ulcerative colitis characteristically shows continuous inflammation beginning at the rectum and extending proximally, unlike the skip lesions and transmural involvement seen in Crohn disease.

Question 27: Berkson's bias is a specific type of selection bias most likely to occur in:

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

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 28: A 10-month-old girl is brought to the physician by her father because she does not seem to be gaining weight despite an increased appetite. He says that she passes 8 to 10 stools daily. She has no history of major medical illness, but during the past winter she had several infections of the ear and respiratory tract that were treated with antibiotics. She appears malnourished but is in no apparent distress. She is at the 5th percentile for length and weight. Diffuse crackles are heard over the lower lung fields on auscultation. Her sweat chloride concentration is 69 mmol/L. Which of the following is the most likely underlying cause of these findings?

Acid phosphatase deficiency
α-l-Fucosidase deficiency
Abnormal cystic fibrosis transmembrane conductance regulator gene function (Correct answer)
Atypical conjugation of arylsulfatase A, B, and C
Impaired production of phosphatidylcholine (lecithins)

Correct answer: Abnormal cystic fibrosis transmembrane conductance regulator gene function

The combination of failure to thrive despite increased appetite, steatorrhea (frequent stools), recurrent respiratory infections (crackles), and a high sweat chloride concentration (69 mmol/L is diagnostic) is pathognomonic for cystic fibrosis. This genetic disorder is caused by mutations in the CFTR gene, leading to abnormal function of the cystic fibrosis transmembrane conductance regulator protein, which impairs chloride transport and results in thick, viscous secretions.

Question 29: 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
Anorexia nervosa
Adjustment disorder with mixed disturbance of emotions and conduct (Correct answer)
Attention-deficit/hyperactivity disorder
Dysthymic disorder

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 30: 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?

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

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 31: An 8-year-old boy is brought to the physician by his mother because he is not paying attention in class. His mother says that his teacher has described his in-school behavior as “frequently stopping what he is doing and then blinking and making chewing movements.” His mother has noticed that he sometimes “stares off into space” and seems to be daydreaming. Physical examination shows no abnormalities. An EEG during one of the episodes shows generalized spike-and-wave bursts at 3 Hz per second. This patient most likely has which of the following types of seizures?

Complex partial
Generalized tonic-clonic
Myoclonic
Absence (Correct answer)
Akinetic

Correct answer: Absence

The description of brief episodes of 'staring off into space,' 'blinking and chewing movements,' and 'stopping what he is doing' without post-ictal confusion, especially in a child, is classic for absence seizures (petit mal). The characteristic 3 Hz generalized spike-and-wave pattern on EEG confirms this diagnosis. Other seizure types, such as generalized tonic-clonic or complex partial seizures, involve different clinical presentations and EEG findings.

Question 32: A patient is found to carry a balanced reciprocal translocation between chromosomes 9 and 22, producing the BCR-ABL fusion gene. Which malignancy is this most associated with?

Chronic myelogenous leukemia (Correct answer)
Burkitt lymphoma
Follicular lymphoma
Acute lymphoblastic leukemia (T-cell)

Correct answer: Chronic myelogenous leukemia

The Philadelphia chromosome t(9;22) creates BCR-ABL, a constitutively active tyrosine kinase that drives CML proliferation and is targeted by imatinib.

Question 33: A 16-year-old girl is brought to the emergency department 6 hours after the onset of moderate lower abdominal cramps and intermittent nausea. She has not vomited during this time. She says that her last menstrual period was 2 months ago, but she has had intermittent bleeding since then, including spotting for the past 2 days. Menarche was at the age of 15 years. Menses occur at irregular 25- to 45-day intervals. She is sexually active and uses condoms inconsistently. Her temperature is 38.1°C (100.6°F), pulse is 94/min, respirations are 22/min, and blood pressure is 120/80 mm Hg. Examination shows a soft abdomen with lower quadrant tenderness, especially on the right. Bowel sounds are normal. Pelvic examination shows scant vaginal bleeding and a palpable, tender right adnexal mass. The cervix appears normal. There is no cervical motion tenderness. Which of the following is the most appropriate next step in management?

Complete blood count
Measurement of serum β-hCG concentration (Correct answer)
Exploratory laparoscopy
Ceftriaxone and azithromycin therapy
Abdominal x-ray

Correct answer: Measurement of serum β-hCG concentration

Given the patient's amenorrhea, irregular bleeding, sexual activity with inconsistent condom use, lower abdominal pain, and a palpable, tender adnexal mass, an ectopic pregnancy must be ruled out immediately. Measuring serum β-hCG concentration is the most appropriate initial diagnostic step to confirm pregnancy and then guide further evaluation (e.g., ultrasound) to determine its location.

Question 34: A 65-year-old man comes to the physician for a follow-up examination after the results of a bronchoscopy showed squamous cell carcinoma. When the physician tells the patient the diagnosis, the patient becomes tearful and responds, “No, you’re wrong! This must be a mistake. This can’t happen to me. Let’s do more tests.” This patient is most likely at which of the following stages of grief?

Depression
Bargaining
Denial (Correct answer)
Anger

Correct answer: Denial

The patient's immediate reaction of disbelief ("No, you’re wrong! This must be a mistake. This can’t happen to me") and desire for more tests to disprove the diagnosis are classic manifestations of denial. Denial is the first stage in Kübler-Ross's model of grief, where individuals struggle to accept the reality of a difficult situation.

Question 35: Neostigmine is used to reverse neuromuscular blockade after surgery. Which agent must always be co-administered with neostigmine to prevent bradycardia?

Atropine (Correct answer)
Pyridostigmine
Epinephrine
Physostigmine

Correct answer: Atropine

Neostigmine inhibits acetylcholinesterase, increasing ACh at all cholinergic synapses; atropine is co-administered to block the unwanted muscarinic (bradycardic) effects.

Question 36: 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?

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

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 37: A 38-year-old woman has progressive dysmenorrhea, dyspareunia, and pelvic pain. Transvaginal ultrasound reveals a 5-cm ovarian cyst with diffuse low-level internal echoes (ground glass appearance). What is the most likely diagnosis?

Tubo-ovarian abscess
Endometrioma (Correct answer)
Mucinous cystadenoma
Mature teratoma (dermoid cyst)

Correct answer: Endometrioma

An endometrioma ('chocolate cyst') presents with endometriosis symptoms and the classic ground-glass ultrasound appearance from accumulated old blood.

Question 38: 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?

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

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 39: A 65-year-old man with coronary artery disease comes to the physician for a follow-up examination. He is 183 cm (6 ft) tall and weighs 84 kg (185 lb); BMI is 25 kg/m2 . His blood pressure is 130/80 mm Hg. The lungs are clear to auscultation. Cardiac examination shows no point of maximal impulse. Serum studies show a glucose concentration of 95 mg/dL and homocysteine concentration of 19.3 μmol/L (N=5–15). Serum lipid concentrations are within the reference range. Which of the following amino acids is most likely to be decreased in this patient?

Lysine
Leucine
Ornithine
Arginine
Methionine (Correct answer)

Correct answer: Methionine

Homocysteine is an intermediate in methionine metabolism. Elevated homocysteine levels often result from deficiencies in enzymes or cofactors (like folate, vitamin B12, or vitamin B6) involved in its remethylation back to methionine or its transsulfuration to cysteine. If homocysteine cannot be efficiently converted back to methionine, then methionine levels would likely be decreased as it is the product of this crucial metabolic pathway.

Question 40: A newborn is noted to have a cardiac murmur. Echo shows blood flowing from the aorta to the pulmonary artery. Which structure has failed to close?

Ductus venosus
Foramen ovale
Truncus arteriosus
Ductus arteriosus (Correct answer)

Correct answer: Ductus arteriosus

Persistent patent ductus arteriosus (PDA) allows left-to-right shunting from the aorta into the pulmonary artery.

Question 41: A 47-year-old man comes to the physician because of a 4-week history of increased thirst and urination. He has had a 23-kg (50-lb) weight gain during the past 2 years. He has no history of serious illness and takes no medications. His mother and maternal grandfather have type 2 diabetes mellitus. The patient does not smoke and drinks one beer every night. He is 175 cm (5 ft 9 in) tall and now weighs 104 kg (230 lb); BMI is 34 kg/m2 . His pulse is 90/min, and blood pressure is 150/88 mm Hg. The remainder of the examination shows no abnormalities. His serum glucose concentration is 330 mg/dL. Which of the following is the most likely underlying cause of this patient’s increased serum glucose concentration?

Pancreatic cancer
Insulin resistance (Correct answer)
Chronic pancreatitis
Exogenous production of corticosteroids
Autoimmune destruction of islet cells

Correct answer: Insulin resistance

This patient presents with classic features of type 2 diabetes mellitus, including significant weight gain leading to obesity (BMI 34), hypertension, and marked hyperglycemia (serum glucose 330 mg/dL). His family history of type 2 diabetes further supports this diagnosis. The underlying cause of type 2 diabetes is primarily insulin resistance, where target cells fail to respond adequately to insulin, leading to compensatory hyperinsulinemia and eventual pancreatic beta-cell exhaustion.

Question 42: A 35-year-old woman delivers a newborn who develops meningitis. The mother has a streptococcus isolated from her vagina. The organism agglutinates with antiserum directed against type B surface carbohydrate. The virulence of this organism is related to a bacterial constituent that interferes with which of the following host phagocyte functions?

Intracellular killing
Chemotaxis
Pseudopod formation
Aggregation
Ingestion (Correct answer)

Correct answer: Ingestion

Group B Streptococcus (GBS), or Streptococcus agalactiae, is a major cause of neonatal meningitis and sepsis. Its primary virulence factor is its polysaccharide capsule, particularly the type B capsule mentioned. This capsule interferes with the host's immune response by preventing the ingestion (phagocytosis) of the bacteria by macrophages and neutrophils. By evading phagocytosis, GBS can survive and proliferate in the host, leading to invasive infections.

Question 43: A 38-year-old woman with MDD fails two adequate trials of SSRIs. She has no contraindications. Which augmentation strategy has the strongest evidence for treatment-resistant depression?

Adding buspirone
Adding methylphenidate
Switching to a tricyclic antidepressant only
Adding lithium or atypical antipsychotic (Correct answer)

Correct answer: Adding lithium or atypical antipsychotic

Augmentation with lithium or atypical antipsychotics (e.g., aripiprazole, quetiapine) has the most robust evidence for treatment-resistant depression.

Question 44: Aminoglycosides such as gentamicin are associated with nephrotoxicity. Which nephron segment is primarily damaged?

Proximal tubule (Correct answer)
Collecting duct
Loop of Henle
Glomerulus

Correct answer: Proximal tubule

Aminoglycosides accumulate in proximal tubular cells via endocytosis and cause direct tubular cell necrosis.

Question 45: A patient cannot extend the wrist or fingers after a midshaft humeral fracture. Which nerve is injured?

Radial nerve (Correct answer)
Median nerve
Musculocutaneous nerve
Ulnar nerve

Correct answer: Radial nerve

The radial nerve runs in the spiral groove of the mid-humerus and innervates all wrist and finger extensors; midshaft fractures commonly injure it.

Question 46: A 12-year-old presents with acute onset headache, fever, and nuchal rigidity. LP shows cloudy CSF, WBC 1200 (90% PMNs), glucose 25 mg/dL, protein 180 mg/dL. Best empiric treatment?

IV acyclovir
IV amphotericin B
Oral amoxicillin
IV ceftriaxone + vancomycin + dexamethasone (Correct answer)

Correct answer: IV ceftriaxone + vancomycin + dexamethasone

Bacterial meningitis requires broad empiric coverage with ceftriaxone, vancomycin, and dexamethasone to reduce inflammation and mortality.

Question 47: 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?

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

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 48: A 28-year-old woman comes to the physician because of a 3-month history of shortness of breath with exertion. She takes an oral contraceptive. There are no occupational exposures to birds or grain dusts. Her respirations are 20/min. The lungs are clear to auscultation. Cardiac examination shows a regular rate and rhythm; S2 is slightly louder than S1 . Cardiac catheterization shows a pulmonary artery pressure of 78/31 mm Hg (N=15–30/3–12) with a normal left ventricular end-diastolic pressure. Which of the following is most likely changed in this patient?

Increased pulmonary vascular resistance (Correct answer)
Decreased alveolar ventilation
Increased pulmonary compliance
Increased muscle tone
Decreased left ventricular afterload

Correct answer: Increased pulmonary vascular resistance

The patient's elevated pulmonary artery pressure (78/31 mm Hg) with a normal left ventricular end-diastolic pressure indicates pre-capillary pulmonary hypertension. This condition is characterized by increased resistance within the pulmonary arterial circulation, rather than issues with the left heart. Oral contraceptive use is a known risk factor for developing pulmonary vascular disease and increased pulmonary vascular resistance.

Question 49: A 57-year-old woman comes to the physician for a routine health maintenance examination. She takes a multivitamin supplement and calcium (500 mg/d). She has followed a vegan diet for 30 years. She exercises daily for 30 minutes. She does not smoke cigarettes or drink alcohol. There is a family history of osteoporosis. She is 168 cm (5 ft 6 in) tall and weighs 60 kg (132 lb); BMI is 21 kg/m2 . Examination shows no abnormalities. Bone densitometry shows evidence of low bone density. She prefers not to be treated with medications. The physician recommends that the patient increase her daily dose of the calcium supplement. The most appropriate next step in management is supplementation with which of the following?

Magnesium
Vitamin D (Correct answer)
Vitamin C
Zinc
Fish oi

Correct answer: Vitamin D

While the patient takes calcium, her long-term vegan diet and family history of osteoporosis put her at increased risk for low bone density. Adequate vitamin D is essential for calcium absorption and bone mineralization. Given her preference against medications and the importance of vitamin D for bone health, supplementation with vitamin D is the most appropriate next step to improve calcium utilization and bone density.

Question 50: A 52-year-old woman whose husband died 2 months ago consults a physician because of headaches and feelings of uncertainty. She describes the headaches as a band around her head; they occur unpredictably and are not accompanied by any other symptoms. She has no history of psychiatric illness. While talking with the physician, the patient begins to cry and talk about her deceased husband; she feels her life is empty now and worries about her future. Which of the following is most appropriate at this point?

Refer her for psychological testing
Obtain a psychiatric consultation
Allow her to express herself (Correct answer)
Prescribe an antianxiety drug
Prescribe an antidepressant drug

Correct answer: Allow her to express herself

The patient is experiencing normal grief reactions following the death of her husband 2 months prior. Her symptoms of sadness, emptiness, crying, and worry are typical responses to such a significant loss. At this stage, the most therapeutic intervention is to provide a supportive environment that allows her to express her feelings and process her grief, rather than immediately medicalizing or pathologizing her experience.

Question 51: After an overnight fast, a 52-year-old man undergoes infusion of acid through a catheter into the upper duodenum. This most likely will increase pancreatic secretion mainly through the action of which of the following substances?

Secretin (Correct answer)
Cholecystokinin
Gastrin
Vasoactive intestinal polypeptide
Glucagon

Correct answer: Secretin

Acidification of the duodenum, as described, is the primary stimulus for the release of secretin from S cells in the duodenal mucosa. Secretin then acts on the pancreatic duct cells to stimulate the secretion of a bicarbonate-rich fluid. This bicarbonate neutralizes the acidic chyme entering the duodenum, creating an optimal pH for the activity of pancreatic digestive enzymes.

Question 52: Furosemide produces diuresis primarily by inhibiting which transporter?

Na+/H+ exchanger in the proximal tubule
Na+/K+-ATPase in collecting duct
Na-K-2Cl cotransporter in the thick ascending limb (Correct answer)
Thiazide-sensitive NaCl cotransporter in the distal tubule

Correct answer: Na-K-2Cl cotransporter in the thick ascending limb

Furosemide blocks the NKCC2 cotransporter in the thick ascending limb, disrupting the countercurrent multiplier and producing copious dilute urine.

Question 53: A 3-year-old is brought in after his mother notices he is not responding to his name, lacks eye contact, lines up toys repetitively, and has no functional speech. Most likely diagnosis?

Intellectual disability
Childhood disintegrative disorder
Selective mutism
Autism spectrum disorder (Correct answer)

Correct answer: Autism spectrum disorder

Autism spectrum disorder is characterized by deficits in social communication and restricted, repetitive behaviors beginning in early childhood.

Question 54: Two days after undergoing surgical repair of a ruptured abdominal aortic aneurysm, a 67-year-old man requires increasing ventilatory support. He remains intubated and is being mechanically ventilated at an FIO2 of 0.6 and a positive end-expiratory pressure of 7.5 cm H2O. He has chronic obstructive pulmonary disease. He had a myocardial infarction 2 years ago. His only medication is a sedative. He has smoked two packs of cigarettes daily for 40 years. He appears diaphoretic. His temperature is 38.1°C (100.6°F), pulse is 120/min, and blood pressure is 90/60 mm Hg; the ventilatory rate is 25/min. Examination shows jugular venous distention. Breath sounds are absent on the left. The trachea is shifted to the right. Pulse oximetry shows an oxygen saturation of 82%. Which of the following is the most appropriate next step in diagnosis?

CT scan of the chest
ECG
Transthoracic echocardiography
Needle aspiration of the left side of the chest (Correct answer)

Correct answer: Needle aspiration of the left side of the chest

The patient is in acute respiratory distress and shock, with absent breath sounds on the left, jugular venous distention, and tracheal deviation to the right. These are classic signs of a tension pneumothorax, a life-threatening condition where air accumulates in the pleural space under pressure, collapsing the lung and shifting mediastinal structures. Immediate needle decompression (aspiration) of the left side of the chest is a life-saving intervention.

Question 55: A 19-year-old woman describes recurrent episodes of binge eating followed by self-induced vomiting. Exam shows parotid enlargement and dental enamel erosion. What electrolyte abnormality is most expected?

Hypokalemia (Correct answer)
Hyperkalemia
Hyperchloremia
Hypernatremia

Correct answer: Hypokalemia

Repeated purging causes loss of hydrochloric acid and potassium, leading to hypokalemic metabolic alkalosis.

Question 56: A 52-year-old woman reports urine leakage with coughing, sneezing, and exercise. Pelvic exam is normal. Urodynamic testing confirms stress urinary incontinence. What is the most appropriate initial management?

Anticholinergic medication (oxybutynin)
Pelvic floor muscle training (Kegel exercises) (Correct answer)
Surgical mid-urethral sling placement
Bladder retraining program

Correct answer: Pelvic floor muscle training (Kegel exercises)

Pelvic floor muscle training is the first-line conservative therapy for stress urinary incontinence, with strong evidence for improving urethral sphincter function.

Question 57: A medical student channels her anxiety about the upcoming board exam into long hours of productive studying. This defense mechanism is best described as:

Rationalization
Intellectualization
Reaction formation
Sublimation (Correct answer)

Correct answer: Sublimation

Sublimation redirects unacceptable impulses into socially acceptable, constructive activities.

Question 58: Xeroderma pigmentosum presents with extreme UV sensitivity and high skin cancer risk. Which DNA repair pathway is defective?

Nucleotide excision repair (NER) (Correct answer)
Mismatch repair (MMR)
Base excision repair (BER)
Non-homologous end joining (NHEJ)

Correct answer: Nucleotide excision repair (NER)

NER removes bulky helix-distorting lesions such as pyrimidine dimers caused by UV radiation; XP mutations in NER endonucleases allow these lesions to persist.

Question 59: A 55-year-old woman who is obese has a greater risk for endometrial carcinoma than a 55-year-old woman with the same health history and status who is not obese. Which of the following best explains this increased risk?

Impairment of immune surveillance by T lymphocytes
Association of obesity with smoking
Greater average number of pregnancies
Accelerated catabolism of antioxidants
Increased production of estrogen by adipose tissue (Correct answer)
Carcinogenic effects of dietary fats
Later age of menopause
More frequent episodes of vaginitis

Correct answer: Increased production of estrogen by adipose tissue

Obesity is a significant risk factor for endometrial carcinoma due to the increased production of estrogen by adipose tissue. Adipose tissue contains the enzyme aromatase, which converts androgen precursors into estrogens. Higher levels of circulating estrogen, particularly unopposed by progesterone, chronically stimulate the endometrium, promoting hyperplasia and increasing the risk of malignant transformation.

Question 60: A 55-year-old man with bipolar I disorder on lithium develops coarse tremor, polyuria, and confusion. His lithium level is 2.8 mEq/L. What is the most appropriate next step?

Reduce lithium dose by half
Switch to valproate immediately
Add benzodiazepine for tremor control
Discontinue lithium and provide supportive care (Correct answer)

Correct answer: Discontinue lithium and provide supportive care

Lithium toxicity at levels above 2.0 mEq/L requires immediate discontinuation; severe toxicity may require hemodialysis.

Question 61: A patient suffers a spinal cord injury and has loss of pain and temperature bilaterally below the lesion, with preserved proprioception and vibration. Upper motor neuron signs are present. Which syndrome is this?

Anterior cord syndrome (Correct answer)
Brown-Séquard syndrome
Posterior cord syndrome
Central cord syndrome

Correct answer: Anterior cord syndrome

Anterior cord syndrome disrupts the spinothalamic tracts (pain/temperature) bilaterally while sparing the posterior columns (proprioception/vibration); typically from anterior spinal artery infarction.

Question 62: Type II pneumocytes in the alveoli are cuboidal cells with lamellar bodies. Their primary function is to produce which substance?

Mucus for airway clearance
Collagen for alveolar scaffolding
Surfactant to reduce alveolar surface tension (Correct answer)
IgA for alveolar defense

Correct answer: Surfactant to reduce alveolar surface tension

Type II pneumocytes synthesize and secrete pulmonary surfactant (dipalmitoylphosphatidylcholine) from lamellar bodies, preventing alveolar collapse.

Question 63: A 48-year-old woman with cirrhosis due to hepatitis C presents with confusion and asterixis. Ammonia level is 180 μmol/L. She is not taking any sedatives. What is the most appropriate initial treatment?

Lactulose orally (Correct answer)
Rifaximin IV
Neomycin IV
Fresh frozen plasma

Correct answer: Lactulose orally

Lactulose is first-line treatment for hepatic encephalopathy; it traps ammonia in the gut by acidifying the colon and promoting its excretion as ammonium.

Question 64: A study reports a p-value of 0.03 with alpha set at 0.05. What is the correct interpretation?

The finding is clinically significant
The study has 97% statistical power
There is a 3% probability the null hypothesis is true
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 65: A 22-year-old man is brought to the ED after a motor vehicle collision with blunt abdominal trauma. He is hypotensive (BP 80/50 mmHg) despite 2L IV crystalloid. FAST exam shows free fluid in the abdomen. What is the next best step?

Abdominal CT scan with contrast
Emergent exploratory laparotomy (Correct answer)
Repeat FAST examination
Diagnostic peritoneal lavage

Correct answer: Emergent exploratory laparotomy

A hemodynamically unstable patient with positive FAST for free abdominal fluid requires immediate exploratory laparotomy without delay for CT.

Question 66: Which connective tissue is characterized by irregularly arranged collagen bundles and is found in the dermis of the skin?

Loose areolar connective tissue
Dense irregular connective tissue (Correct answer)
Elastic connective tissue
Dense regular connective tissue

Correct answer: Dense irregular connective tissue

Dense irregular connective tissue has randomly oriented collagen bundles that resist tension from multiple directions, as in the dermis.

Question 67: 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?

Prophylactic oophorectomy
Obtain a more detailed family history of cancer (Correct answer)
Annual CT scans of the abdomen
Recommend a diet high in beta-carotene
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 68: A 77-year-old man comes to the physician because of swelling of his legs and feet for 6 months. He has a 40-year history of alcoholism and a 5-year history of hepatic disease. Physical examination shows ascites and a 2+ edema of the lower extremities. A decrease in which of the following most likely promotes edema formation in this patient?

Plasma colloid oncotic pressure (Correct answer)
Capillary hydrostatic pressure
Interstitial fluid hydrostatic pressure (Correct answer)
Filtration coefficient
Interstitial colloid osmotic pressure

Correct answer: Plasma colloid oncotic pressure

Chronic liver disease, often seen in alcoholism, impairs the liver's ability to synthesize albumin, the main plasma protein. A decrease in plasma albumin leads to a significant reduction in plasma colloid oncotic pressure. This reduced oncotic pressure diminishes the force that draws fluid back into the capillaries, causing fluid to leak into the interstitial space and peritoneum (ascites), thereby promoting edema formation.

Question 69: 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?

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

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 70: A 22-year-old college student develops fever, pharyngitis, and posterior cervical lymphadenopathy. A peripheral blood smear shows atypical lymphocytes. The heterophile antibody test is positive. Which cell type is the primary reservoir for the causative virus?

T lymphocytes
Monocytes
B lymphocytes (Correct answer)
Epithelial cells

Correct answer: B lymphocytes

Epstein-Barr virus (EBV) infects B lymphocytes via CD21 (complement receptor 2); the atypical lymphocytes seen on smear are reactive cytotoxic T cells responding to infected B cells.

Question 71: A traveler returns from sub-Saharan Africa with cyclic fever every 48 hours, severe anemia, and splenomegaly. Thick blood smear shows ring forms and banana-shaped gametocytes. Which organism is responsible?

Plasmodium vivax
Plasmodium ovale
Plasmodium malariae
Plasmodium falciparum (Correct answer)

Correct answer: Plasmodium falciparum

Plasmodium falciparum is identified by multiple ring forms per RBC, banana-shaped gametocytes, and a 48-hour (tertian) fever cycle; it causes the most severe malaria and can infect RBCs of all ages.

Question 72: Beta-oxidation of an 18-carbon fully saturated fatty acid yields how many acetyl-CoA molecules?

7
9 (Correct answer)
10
8

Correct answer: 9

An 18-carbon fatty acid undergoes 8 rounds of beta-oxidation, producing 9 acetyl-CoA molecules (each 2-carbon unit released as acetyl-CoA).

Question 73: 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
Meckel diverticulum (Correct answer)
Umbilical hernia
Retrocecal appendix
Carcinoid tumor

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 74: A 52-year-old man with end-stage renal disease receives a deceased-donor kidney transplant. On postoperative day 7, serum creatinine rises from 2.1 to 4.5 mg/dL and urine output decreases. Ultrasound shows normal vascularity. Biopsy reveals lymphocytic infiltration of the tubules and interstitium. What is the treatment?

Graft nephrectomy
Increase maintenance tacrolimus dose
High-dose IV corticosteroids (pulse methylprednisolone) (Correct answer)
Plasmapheresis and IVIG

Correct answer: High-dose IV corticosteroids (pulse methylprednisolone)

Acute cellular rejection (T-cell mediated) after renal transplant is treated with pulse IV corticosteroids as first-line therapy.

Question 75: A 6-year-old boy repeatedly wets the bed at night despite normal development. What is the first-line behavioral intervention for primary enuresis?

Desmopressin at bedtime
Imipramine
Urine alarm (bell-and-pad) therapy (Correct answer)
Oxybutynin

Correct answer: Urine alarm (bell-and-pad) therapy

The urine (enuresis) alarm has the highest long-term cure rate and is first-line behavioral treatment for primary nocturnal enuresis.

Question 76: A previously healthy 15-year-old girl comes to the physician because of increasing left ear pain during the past 3 days. Vital signs are within normal limits. Examination of the left ear shows edema and erythema of the auditory canal with a greenish discharge. Manipulation of the left pinna elicits pain. The tympanic membrane can only partially be visualized, and examination of what can be seen appears normal with normal mobility. Examination of the right ear shows no abnormalities. Which of the following is the most likely diagnosis?

Mastoiditis
Furunculosis
Acute otitis media
Otitis externa (Correct answer)
Tympanic membrane perforation

Correct answer: Otitis externa

The patient's symptoms of ear pain, edema and erythema of the auditory canal, greenish discharge, and pain elicited by manipulation of the pinna are classic signs of otitis externa, also known as 'swimmer's ear.' This infection or inflammation of the external auditory canal typically spares the tympanic membrane, which appears normal or only partially visualized due to canal swelling.

Question 77: A patient with homocystinuria due to cystathionine beta-synthase deficiency presents with lens dislocation and thromboembolism. High-dose supplementation with which vitamin may reduce homocysteine levels in responsive patients?

Riboflavin (B2)
Cobalamin (B12)
Thiamine (B1)
Pyridoxine (B6) (Correct answer)

Correct answer: Pyridoxine (B6)

Cystathionine beta-synthase requires PLP (vitamin B6) as a cofactor; high-dose B6 increases residual enzyme activity in responsive patients.

Question 78: 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?

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

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

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

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 80: A dataset has a mean, median, and mode that are all equal. Which of the following BEST describes this distribution?

Normal (bell-shaped) (Correct answer)
Negatively skewed
Bimodal
Positively skewed

Correct answer: Normal (bell-shaped)

When mean, median, and mode are equal, the distribution is symmetric and follows a normal (Gaussian) bell-shaped curve.

Question 81: A 48-year-old woman with rheumatoid arthritis on prednisone 10 mg/day for 2 years has a DEXA T-score of −2.7 at the lumbar spine and no prior fractures. What is the most appropriate treatment?

Alendronate plus calcium and vitamin D (Correct answer)
Calcium and vitamin D supplementation only
Teriparatide SC injection
Raloxifene

Correct answer: Alendronate plus calcium and vitamin D

Glucocorticoid-induced osteoporosis with T-score below −2.5 warrants bisphosphonate therapy plus calcium and vitamin D.

Question 82: A 7-year-old boy fails to develop spoken language, avoids eye contact, and engages in repetitive rocking movements. He was hitting all developmental milestones until age 18 months. What is the most likely diagnosis?

Fragile X syndrome
Selective mutism
Rett syndrome
Autism spectrum disorder (Correct answer)

Correct answer: Autism spectrum disorder

Autism spectrum disorder presents with deficits in social communication and restricted/repetitive behaviors; early development may appear normal before regression.

Question 83: A 37-year-old man with type 1 diabetes mellitus comes to the physician for a routine examination. His only medication is insulin. His pulse is 72/min, respirations are 12/min, and blood pressure is 138/88 mm Hg. Funduscopic examination shows microaneurysms and hemorrhages. Sensation to vibration and light touch is decreased over the lower extremities. His serum creatinine concentration is 1.6 mg/dL. A 24-hour urine collection shows 550 mg of protein. Treatment with which of the following is most likely to slow progression of this patient’s renal disease?

Atenolol
Clonidine
Hydralazine
Hydrochlorothiazide
Lisinopril (Correct answer)

Correct answer: Lisinopril

The patient has evidence of diabetic nephropathy, characterized by proteinuria and elevated serum creatinine. Angiotensin-converting enzyme (ACE) inhibitors, such as lisinopril, are the cornerstone of treatment for diabetic nephropathy. They reduce intraglomerular pressure by dilating the efferent renal arteriole, thereby decreasing proteinuria and significantly slowing the progression of renal disease.

Question 84: A 4-year-old boy presents with a painless right-sided abdominal mass that does not cross the midline. His BP is 140/90 mmHg. Ultrasound shows a 6-cm solid intrarenal mass. What is the most likely diagnosis and next step?

Neuroblastoma; bone marrow biopsy
Renal abscess; IV antibiotics and drainage
Renal cell carcinoma; partial nephrectomy
Wilms tumor (nephroblastoma); surgical resection and adjuvant therapy (Correct answer)

Correct answer: Wilms tumor (nephroblastoma); surgical resection and adjuvant therapy

A solid intrarenal mass in a child aged 3–5 that does not cross the midline is most likely Wilms tumor, treated with nephrectomy plus adjuvant chemotherapy/radiation per stage.

Question 85: 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?

Rh incompatibility hemolytic disease
ABO incompatibility hemolytic disease (Correct answer)
Breast milk jaundice
Physiologic 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 86: Pain and temperature from the body ascend to the thalamus via which pathway, and where do they first synapse after entering the spinal cord?

Lateral spinothalamic tract; dorsal horn (Rexed laminae I and V) (Correct answer)
Corticospinal tract; anterior horn motor neurons
Dorsal column–medial lemniscal pathway; nucleus gracilis/cuneatus
Spinocerebellar tract; Clarke's nucleus (lamina VII)

Correct answer: Lateral spinothalamic tract; dorsal horn (Rexed laminae I and V)

Pain and temperature fibers (Aδ and C) synapse in ipsilateral dorsal horn laminae I and V, decussate in the anterior commissure within 1-2 levels, and ascend in the contralateral lateral spinothalamic tract to the VPL thalamus.

Question 87: 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?

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

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 88: A patient receiving a β2-agonist inhaler for asthma notices that the same dose produces less bronchodilation after 2 weeks of continuous use. This phenomenon is best described as:

Idiosyncratic reaction unique to this patient's genotype
Tachyphylaxis caused by increased drug metabolism
Drug resistance from mutation of the β2 receptor gene
Tolerance due to receptor desensitization and downregulation (Correct answer)

Correct answer: Tolerance due to receptor desensitization and downregulation

Prolonged agonist exposure causes receptor phosphorylation, uncoupling from G-proteins, and downregulation of receptor number, reducing drug response over time.

Question 89: A stab wound to the posterior triangle of the neck results in weakness of shoulder elevation and head rotation. Which nerve is damaged?

Phrenic nerve
Long thoracic nerve
Dorsal scapular nerve
Accessory nerve (CN XI) (Correct answer)

Correct answer: Accessory nerve (CN XI)

The accessory nerve (CN XI) traverses the posterior triangle and innervates the trapezius (shoulder elevation) and sternocleidomastoid (head rotation).

Question 90: Which organism is responsible for gas gangrene and produces an alpha toxin (lecithinase) that destroys cell membranes by cleaving phospholipids?

Clostridium tetani
Clostridium perfringens (Correct answer)
Clostridium difficile
Clostridium botulinum

Correct answer: Clostridium perfringens

Clostridium perfringens produces alpha toxin (a phospholipase C/lecithinase) that hydrolyzes phosphatidylcholine in cell membranes, causing myonecrosis and hemolysis.

Question 91: One day after admission to the hospital for agitation and hallucinations, a 19-year-old man has the onset of severe muscle stiffness that prevents him from rising out of bed. At the time of admission, treatment with haloperidol was begun. Today, he appears lethargic and diaphoretic. His temperature is 39.7°C (103.5°F), pulse is 120/min, and blood pressure is 160/110 mm Hg. Physical examination shows generalized severe rigidity of the upper extremities bilaterally. On mental status examination, he is not oriented to person, place, and time. Which of the following is the most appropriate next step in management?

Increase the dosage of haloperidol
Observation only
Add lithium carbonate
Discontinue haloperidol (Correct answer)
Add fluoxetine

Correct answer: Discontinue haloperidol

The patient's symptoms—severe muscle rigidity, hyperthermia (39.7°C), autonomic instability (tachycardia, hypertension, diaphoresis), and altered mental status—developing shortly after starting haloperidol are classic signs of Neuroleptic Malignant Syndrome (NMS). The most critical initial step in managing NMS is to immediately discontinue the offending antipsychotic medication to prevent further progression and complications.

Question 92: 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 IV collagen
Type II 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 93: A 52-year-old woman living in Maryland comes to the physician because of a 1-week history of low-grade fever, fatigue, and a red rash over the skin behind her left knee. She is an avid hiker. Her temperature is 38°C (100.4°F). Physical examination shows an 8-cm, warm, nontender, erythematous lesion with partial central clearing over the skin of the left popliteal area. Which of the following is the most likely causal organism?

Streptobacillus moniliformis
Borrelia burgdorferi (Correct answer)
Ehrlichia chaffeensis
Rickettsia rickettsii
Francisella tularensis

Correct answer: Borrelia burgdorferi

The patient's history of hiking in Maryland, an area endemic for Lyme disease, combined with the characteristic 'bull's-eye' rash (erythema migrans) that is warm, nontender, and has partial central clearing, strongly indicates Lyme disease. Lyme disease is caused by the spirochete Borrelia burgdorferi, transmitted by Ixodes ticks. The associated low-grade fever and fatigue are also consistent early symptoms of this infection.

Question 94: During isovolumetric contraction, which valves are open?

Aortic valve only
Neither aortic nor mitral valves (Correct answer)
Mitral valve only
Both aortic and mitral valves

Correct answer: Neither aortic nor mitral valves

During isovolumetric contraction, all four cardiac valves are closed as ventricular pressure rises before the aortic valve opens.

Question 95: A 65-year-old man undergoes colectomy for colorectal carcinoma. Pathology shows a tumor that is confined to the muscularis propria with 2 positive regional lymph nodes. What is this lesion's TNM stage?

T2 N0 M0 (Stage II)
T3 N0 M0 (Stage II)
T1 N0 M0 (Stage I)
T2 N1 M0 (Stage III) (Correct answer)

Correct answer: T2 N1 M0 (Stage III)

T2 indicates invasion into but not through the muscularis propria; N1 indicates 1-3 positive regional nodes; M0 = no distant metastasis = Stage III.

Question 96: Where is the majority (~80–85%) of filtered bicarbonate reabsorbed?

Thick ascending limb
Collecting duct
Distal convoluted tubule
Proximal convoluted tubule (Correct answer)

Correct answer: Proximal convoluted tubule

The proximal tubule reabsorbs ~80–85% of filtered HCO3- via carbonic anhydrase-dependent H+ secretion and HCO3-/Na+ cotransport.

Question 97: A study is conducted to assess the benefits of a new drug to reduce the recurrence of colonic polyps. The results show a number needed to treat (NNT) of 16. Which of the following is the most accurate interpretation of this result?

For every 16 patients treated, 1 would benefit from the new drug (Correct answer)
For every 100 patients treated, 16 would benefit from the new drug
93% of patients taking the new drug would benefit from it
84% of patients taking the new drug would not have any benefit from it
The new drug is 1.6 times more beneficial than a placebo

Correct answer: For every 16 patients treated, 1 would benefit from the new drug

The Number Needed to Treat (NNT) is a crucial epidemiological measure that quantifies the effectiveness of a medical intervention. It represents the average number of patients who need to be treated with a specific intervention for one additional patient to experience a beneficial outcome, compared to a control group. Therefore, an NNT of 16 means that for every 16 patients treated with the new drug, one patient will benefit.

Question 98: A 3-year-old boy is brought to the physician because of a 2-day history of fever and an itchy rash. The rash began on his face and then spread to his trunk, arms, and legs. Several children at his day-care center have had similar symptoms. His temperature is 38.9°C (102°F), pulse is 100/min, respirations are 20/min, and blood pressure is 110/60 mm Hg. Physical examination shows multiple red papules and vesicles over the face, trunk, and upper and lower extremities. Some vesicles contain clear fluid, whereas others are crusted. Which of the following is the most likely causal virus?

Human papillomavirus
Herpes simplex virus 2
Varicella-zoster virus (Correct answer)
Epstein-Barr virus
Cytomegalovirus

Correct answer: Varicella-zoster virus

The clinical presentation of a febrile illness with a highly pruritic rash that starts on the face/trunk and spreads centrifugally, characterized by lesions in various stages of development (papules, vesicles, crusts—'dewdrop on a rose petal' appearance), is classic for varicella (chickenpox). This highly contagious disease is caused by the varicella-zoster virus (VZV) and commonly spreads in settings like day-care centers.

Question 99: A 28-year-old woman develops a frothy, malodorous vaginal discharge with a pH of 5.5. Wet mount shows motile, pear-shaped organisms with flagella. Which drug is used for treatment?

Clotrimazole
Clindamycin
Fluconazole
Metronidazole (Correct answer)

Correct answer: Metronidazole

Trichomonas vaginalis is a flagellated protozoan treated with metronidazole (or tinidazole); the drug forms free radical intermediates that damage DNA in anaerobic organisms.

Question 100: A 30-year-old woman comes to the physician because of a 2-month history of unsteady gait and numbness of both legs. Eight years ago, she underwent resection of the terminal ileum because of severe Crohn disease. Physical examination shows mild spastic weakness. Sensation to pinprick, vibration, and fine touch is decreased in the upper and lower extremities. A deficiency of which of the following is the most likely underlying cause of these findings?

Iron
Protein
Folic acid
Vitamin B1 (thiamine)
Vitamin B12 (cobalamin) (Correct answer)

Correct answer: Vitamin B12 (cobalamin)

Resection of the terminal ileum, as seen in severe Crohn disease, significantly impairs the absorption of vitamin B12 (cobalamin), which is the primary site for its absorption. A deficiency in vitamin B12 can lead to subacute combined degeneration of the spinal cord, causing demyelination of the dorsal columns (impaired vibration/proprioception) and lateral corticospinal tracts (spastic weakness), explaining the patient's neurological symptoms.

Question 101: A 57-year-old woman comes to the physician for a routine follow-up examination. She has a 5-year history of hypertension treated with captopril. She has had a 6.8-kg (15-lb) weight gain since her last visit 1 year ago; she is 165 cm (5 ft 5 in) tall and currently weighs 72 kg (160 lb); BMI is 27 kg/m2 . Her temperature is 37°C (98.6°F), pulse is 88/min, respirations are 14/min, and blood pressure is 160/86 mm Hg. The lungs are clear to auscultation. Cardiac examination shows no abnormalities. The abdomen is soft and nontender with no palpable masses. Pedal pulses and sensation to pinprick are diminished bilaterally. Fasting serum studies show a total cholesterol concentration of 240 mg/dL and glucose concentration of 182 mg/dL. Which of the following is the most likely cause of these findings?

Excess glycogen breakdown
Excess release of glucagon and catecholamines
Insulin allergy
Autoimmune β-cell destruction
Abnormal insulin secretion with insulin resistance (Correct answer)

Correct answer: Abnormal insulin secretion with insulin resistance

The patient presents with several features of metabolic syndrome and type 2 diabetes: overweight (BMI 27), hypertension, dyslipidemia (high cholesterol), and elevated fasting glucose (182 mg/dL). Type 2 diabetes is characterized by a combination of insulin resistance, where target cells do not respond effectively to insulin, and a progressive decline in pancreatic beta-cell function leading to insufficient insulin secretion. This leads to hyperglycemia and associated complications like peripheral neuropathy and peripheral artery disease.

Question 102: 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?

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

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 103: A 62-year-old man is being treated with cisplatin for small cell carcinoma of the lungs. The efficacy of cisplatin depends on interaction with which of the following?

Ribosomes
Reverse transcriptase
DNA polymerase
DNA (Correct answer)
Growth factor receptors

Correct answer: DNA

Cisplatin is a platinum-based antineoplastic agent used in chemotherapy. Its efficacy stems from its ability to form highly reactive platinum complexes that bind to and cross-link DNA strands within cancer cells. This DNA damage inhibits DNA replication and transcription, ultimately leading to apoptosis of rapidly dividing tumor cells, making it effective against small cell carcinoma of the lungs.

Question 104: A 60-year-old postmenopausal woman has a 2-year history of vulvar pruritus. Exam shows white, atrophic, crinkled plaques. Biopsy shows epidermal thinning with a band of homogeneous collagen (sclerosis) in the upper dermis. What is the diagnosis?

Lichen simplex chronicus
Vulvar intraepithelial neoplasia (VIN)
Vulvar squamous cell carcinoma
Lichen sclerosus (Correct answer)

Correct answer: Lichen sclerosus

Lichen sclerosus is characterized by white atrophic plaques and the pathognomonic biopsy finding of epidermal thinning with a homogeneous sclerotic (hyalinized) collagen band in the dermis.

Question 105: A toddler develops hypoglycemia, jaundice, and vomiting after eating fruit. Fructose-1-phosphate accumulates in the liver. The deficient enzyme is:

Phosphofructokinase-1
Fructose-1,6-bisphosphatase
Fructokinase
Aldolase B (Correct answer)

Correct answer: Aldolase B

Hereditary fructose intolerance is caused by aldolase B deficiency, trapping fructose-1-phosphate in the liver and depleting free phosphate and ATP.

Question 106: Cyclosporine is used to prevent organ rejection. Which mechanism accounts for its immunosuppressive action?

Blocks purine synthesis via IMPDH inhibition
Inhibits calcineurin, preventing IL-2 transcription in T cells (Correct answer)
Depletes B cells by blocking CD20 antigen
Blocks mTOR pathway, inhibiting T-cell proliferation

Correct answer: Inhibits calcineurin, preventing IL-2 transcription in T cells

Cyclosporine binds cyclophilin to form a complex that inhibits calcineurin, preventing NFAT dephosphorylation and IL-2 gene transcription in T cells.

Question 107: A 67-year-old smoker with known COPD presents with worsened dyspnea and increased yellow sputum production. ABG shows pH 7.32, PaCO2 58, PaO2 54. What is the most appropriate initial oxygen target?

No supplemental oxygen until intubated
SpO2 >98% via non-rebreather mask
SpO2 88–92% via controlled low-flow oxygen (Correct answer)
SpO2 >95% via Venturi mask at 60%

Correct answer: SpO2 88–92% via controlled low-flow oxygen

COPD patients with hypercapnia should receive controlled low-flow oxygen targeting SpO2 88–92% to avoid suppressing the hypoxic respiratory drive.

Question 108: The standard error of the mean (SEM) is calculated as:

Standard deviation divided by the square root of n (Correct answer)
Variance divided by sample size
Mean divided by standard deviation
Standard deviation multiplied by the square root of n

Correct answer: Standard deviation divided by the square root of n

SEM = SD / √n; it estimates how much the sample mean would vary across repeated samples drawn from the same population.

Question 109: A 70-year-old man is brought to the emergency department because of a 1-week history of increasingly severe left-sided lower abdominal pain and passing gas in his urine. His temperature is 38.9°C (102°F). A CT scan of the abdomen shows gas in the bladder and edema of the fat surrounding the sigmoid colon. There is no obvious lymph node enlargement. Which of the following is the most likely cause of this patient’s condition?

Urinary tract infection
Prostate cancer with fistula
Diverticulitis with fistula (Correct answer)
Bladder infection
Appendicitis with fistula

Correct answer: Diverticulitis with fistula

Left-sided lower abdominal pain and fever are characteristic of diverticulitis. The key symptom here is pneumaturia (passing gas in urine), which indicates a fistula between the bowel and the bladder. Given the location and the CT findings of edema around the sigmoid colon and gas in the bladder, a colovesical fistula secondary to diverticulitis is the most likely diagnosis.

Question 110: A 22-year-old woman comes to the physician because of a 1-day history of fever and right flank pain. Her temperature is 39°C (102.2°F). Physical examination shows right flank tenderness. Urinalysis shows bacteria, numerous WBC/hpf, and WBC casts. Complete blood count shows leukocytosis. Which of the following is the most likely diagnosis?

Vaginitis
Pyelonephritis (Correct answer)
Cervicitis
Urethritis
Cystitis

Correct answer: Pyelonephritis

The patient's presentation with fever, flank pain, and tenderness, along with urinalysis findings of bacteria, numerous white blood cells, and specifically white blood cell casts, is classic for acute pyelonephritis. WBC casts indicate inflammation within the renal tubules, localizing the infection to the kidney parenchyma rather than just the bladder or urethra. Leukocytosis further supports a systemic inflammatory response.

Question 111: A 32-year-old woman, gravida 2, para 2, develops fever and left lower abdominal pain 3 days after delivery of a full-term male newborn. Abdominal examination shows a tender, palpable mass. Ultrasonography of the mass shows an ovarian vein thrombosis. The thrombus is most likely to extend into which of the following veins?

Left internal pudendal vein
Inferior vena cava
Hemiazygos vein
Left renal vein (Correct answer)
Left internal iliac vein

Correct answer: Left renal vein

The left ovarian vein drains into the left renal vein, whereas the right ovarian vein drains directly into the inferior vena cava. Therefore, a thrombus originating in the left ovarian vein would naturally extend proximally along its anatomical drainage pathway. This means the thrombus is most likely to propagate into the left renal vein. Postpartum ovarian vein thrombosis is a rare but serious complication, and understanding the venous anatomy is crucial for predicting its extension.

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

62%

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