MD Medical Doctor General 4 — Questions and Answers
Question 1: A 35-year-old woman presents with progressive muscle weakness that worsens with activity and improves with rest. Edrophonium test is positive. What is the underlying mechanism?
- Autoantibodies against voltage-gated calcium channels at the NMJ
- Autoantibodies against acetylcholine receptors at the NMJ (Correct answer)
- Demyelination of motor neurons
- Degeneration of upper motor neurons
Correct answer: Autoantibodies against acetylcholine receptors at the NMJ
Myasthenia gravis is caused by autoantibodies against nicotinic acetylcholine receptors at the neuromuscular junction, causing fatigable muscle weakness.
Question 2: Which finding best differentiates nephrotic syndrome from nephritic syndrome?
- Hematuria and hypertension
- Proteinuria >3.5 g/day with hypoalbuminemia and edema (Correct answer)
- Oliguria and azotemia
- Red cell casts in urine
Correct answer: Proteinuria >3.5 g/day with hypoalbuminemia and edema
Nephrotic syndrome is defined by massive proteinuria (>3.5 g/day), hypoalbuminemia, edema, and hyperlipidemia, whereas nephritic syndrome features hematuria and red cell casts.
Question 3: A 50-year-old alcoholic presents with confusion, ataxia, and ophthalmoplegia. Which vitamin deficiency is responsible?
- Vitamin B12 (cobalamin)
- Vitamin B1 (thiamine) (Correct answer)
- Vitamin B6 (pyridoxine)
- Niacin (B3)
Correct answer: Vitamin B1 (thiamine)
Wernicke's encephalopathy is caused by thiamine (B1) deficiency, presenting with the classic triad of confusion, ataxia, and ophthalmoplegia; treat with IV thiamine.
Question 4: A newborn is noted to have a continuous machinery murmur at the left upper sternal border. Which congenital heart defect is most likely?
- Ventricular septal defect
- Patent ductus arteriosus (Correct answer)
- Atrial septal defect
- Tetralogy of Fallot
Correct answer: Patent ductus arteriosus
Patent ductus arteriosus produces a continuous 'machinery' murmur due to persistent shunting between the aorta and pulmonary artery throughout the cardiac cycle.
Question 5: A 28-year-old woman in her third trimester develops severe headache, blurry vision, and BP of 160/110 mmHg. Urinalysis shows 3+ proteinuria. What is the most appropriate management?
- Strict bed rest and oral antihypertensives only
- IV magnesium sulfate for seizure prophylaxis and delivery planning (Correct answer)
- Emergent cesarean section without medications
- Observation and recheck in 24 hours
Correct answer: IV magnesium sulfate for seizure prophylaxis and delivery planning
Severe preeclampsia requires IV magnesium sulfate to prevent eclamptic seizures and antihypertensives, with delivery being the definitive treatment.
Question 6: Which type of hypersensitivity reaction underlies anaphylaxis?
- Type II (cytotoxic)
- Type III (immune complex)
- Type I (IgE-mediated) (Correct answer)
- Type IV (delayed/cell-mediated)
Correct answer: Type I (IgE-mediated)
Anaphylaxis is a Type I hypersensitivity reaction mediated by IgE antibodies on mast cells and basophils, causing immediate release of histamine and other mediators.
Question 7: A patient taking warfarin presents with a supratherapeutic INR of 9.0 but no active bleeding. What is the most appropriate immediate management?
- Administer fresh frozen plasma
- Hold warfarin and give oral vitamin K (Correct answer)
- Give protamine sulfate
- Administer tranexamic acid
Correct answer: Hold warfarin and give oral vitamin K
For significantly elevated INR without bleeding, holding warfarin and administering oral vitamin K is appropriate to reverse anticoagulation safely.
MD Medical Doctor General 4
A 35-year-old woman presents with progressive muscle weakness that worsens with activity and improves with rest.
Edrophonium test is positive.
What is the underlying mechanism?