Autonomic Pharmacology USMLE Step 1 Practice Question
A 35-year-old woman with myasthenia gravis treated with pyridostigmine presents to the emergency department with acute onset of generalized weakness, diplopia, and respiratory distress. Vital signs: BP 128/82, HR 102, RR 28, SpO2 88%. Physical examination reveals miosis, visible muscle fasciculations, and generalized flaccid paralysis. Muscle strength testing shows grade 2/5 throughout. The patient's caregiver reports she has been increasing her pyridostigmine dose on her own over the past week because she felt her symptoms were worsening. Bedside spirometry shows FVC of 1.2 L (baseline 3.8 L). Which of the following clinical findings would most reliably distinguish a cholinergic crisis from a myasthenic crisis in this patient?
Answer choices
- AResponse to intravenous edrophonium (Tensilon test) with temporary improvement in strengthCorrect answer
- BPresence of miosis and muscle fasciculations indicating excessive acetylcholine
- CElevated serum creatine kinase and myoglobinuria from excessive muscle contraction
- DAbsence of sweating and bronchospasm, indicating insufficient cholinergic stimulation
- EBradycardia and hypotension reflecting parasympathetic predominance
- FPupillary light reflex that remains intact despite presence of miosis
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