A 34-year-old man comes to the hospital due to several hours of difficulty swallowing, dry mouth, and blurred vision. The patient has a history of major depression. Examination shows mydriasis and poorly reactive pupils. Electrodiagnostic studies reveal normal nerve conduction velocity but decreased compound muscle action potential (CMAP). Rapid, repetitive nerve stimulation leads to facilitation of CMAP. Further review of this patient's medical history would most likely reveal which of the following?

Question

A 34-year-old man comes to the hospital due to several hours of difficulty swallowing, dry mouth, and blurred vision.  The patient has a history of major depression.  Examination shows mydriasis and poorly reactive pupils.  Electrodiagnostic studies reveal normal nerve conduction velocity but decreased compound muscle action potential (CMAP).  Rapid, repetitive nerve stimulation leads to facilitation of CMAP.  Further review of this patient's medical history would most likely reveal which of the following?

Quizplus · Accepted Answer

Eductional Objective: Botulinum neurotoxin produced by Clostridium botulinum prevents the release of acetylcholine from presynaptic nerve terminals.  The toxin impairs peripheral muscarinic and nicotinic neurotransmission, causing both autonomic symptoms (eg, fixed pupillary dilation, dry mouth) and skeletal muscle weakness (eg, diplopia, dysphagia, respiratory depression).  Its effects at the neuromuscular junction can be seen on electromyography as a decrease in muscle response following stimulation of a motor nerve.

A 34-Year-Old Man Comes to the Hospital Due to Several