A male patient presents to your primary care clinic with the following symptoms: foot drop and progressive motor weakness of the lower extremities, with difficulty swallowing. The patient has no numbness or back pain, no bowel or bladder incontinence, no blurred vision. The patient has a history of tobacco use. What disease process is most likely the cause of the patient's symptoms?
1. Amyotrophic lateral sclerosis (ALS).
2. Multiple sclerosis (MS).
3. Parkinson disease.
4. Lumbar spine disc herniation.