question: Q:A 46-year-old man comes to the physician because of a 2-month history of hoarseness and drooling. Initially, he had difficulty swallowing solid food, but now he has difficulty swallowing foods like oatmeal as well. During this period, he also developed weakness in both arms and has had an 8.2 kg (18 lb) weight loss. He appears ill. His vital signs are within normal limits. Examination shows tongue atrophy and pooled oral secretions. There is diffuse muscle atrophy in all extremities. Deep tendon reflexes are 3+ in all extremities. Sensation to pinprick, light touch, and vibration is intact. An esophagogastroduodenoscopy shows no abnormalities. Which of the following is the most likely cause of this patient's symptoms?? 
  {'A': 'Multiple cerebral infarctions', 'B': 'Autoimmune destruction of acetylcholine receptors', 'C': 'Demyelination of peripheral nerves', 'D': 'Destruction of upper and lower motor neurons', 'E': 'Dilation of the central spinal canal'},