A 54-Year-Old Man Comes to the Physician for the Evaluation

A 54-year-old man comes to the physician for the evaluation of difficulty swallowing solid food and liquids for 1 month. During the past 5 months, he has also had increased weakness of his hands and legs. He sails regularly and is unable to hold the ropes as tightly as before. Ten years ago, he was involved in a motor vehicle collision. Examination shows atrophy of the tongue. Muscle strength is decreased in the right upper and lower extremities. There is muscle stiffness in the left lower extremity. Deep tendon reflexes are 1+ in the right upper and lower extremities, 3+ in the left upper extremity, and 4+ in the left lower extremity. Plantar reflex shows an extensor response on the left foot. Sensation to light touch, pinprick, and vibration is intact. Which of the following is the most likely diagnosis?

A) Amyotrophic lateral sclerosis
B) Poliomyelitis
C) Rabies
D) Huntington disease
E) Friedreich ataxia
F) Vitamin B₁₂ deficiency