Neuromuscular Disorders USMLE Step 1 Practice Question
A 26-year-old man presents with severe diffuse myalgias, abdominal cramping, and diaphoresis after sustaining a spider bite while cleaning a garage. Vital signs show BP 158/94 mmHg, HR 112 bpm, RR 18/min, and temp 37.2°C. Examination reveals generalized muscle rigidity and fasciculations. Serum creatine kinase is elevated at 890 U/L. There is no rash or neurologic deficit. Which toxin best explains these clinical findings?
Answer choices
- AAutoimmune destruction of nicotinic receptors
- BBlockade of voltage gated sodium channels in peripheral nerves
- CIrreversible inhibition of acetylcholinesterase
- DInhibition of acetylcholine release at the neuromuscular junction
- EMassive presynaptic release of acetylcholine and norepinephrineCorrect answer
- FDermonecrotic toxin causing local ischemia and muscle damage (brown recluse spider)
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.