Neuromuscular junction disorders Quiz: Ace Your Exams

A 57-year-old man comes to his primary care provider for evaluation of muscle weakness. The symptoms began four months ago. The patient reports the weakness is most prominent in the thighs. Past medical history is notable for hypertension and type I diabetes mellitus, for which he takes daily amlodipine and insulin injections. Social history is notable for a 40-pack-year smoking history. In the office, his temperature is 37.0°C (98.6°F), pulse is 71/min, and blood pressure is 152/83 mmHg. Physical examination shows weakness in the quadriceps bilaterally and 3/5 patellar reflexes. The patient is asked to walk back-and-forth several times across the examination room. Repeat testing reveals 5/5 patellar reflexes. No sensory deficits are observed. Cardiac, pulmonary, and abdominal exams are noncontributory. Laboratory testing reveals a creatinine kinase of 80 U/L and erythrocyte sedimentation rate of 12 mm/h. Which of the following best describes the pathophysiology of this patient’s condition?