Not Quite Textbook I

My favorite blogs are about some of the fascinating cases I've seen. Patient identifiers have all been changed for these cases.

A 40 year old man with a past medical history significant for bipolar disease and hypertension was brought into the emergency department by a roommate for several weeks of worsening functional status. He's become more and more confused, sometimes unsure where he is. But rather than becoming agitated, he's become more and more withdrawn with decreased interactiveness and a soft voice. By soft voice, I mean serious hypophonia; he whispered so quietly you had to lean in to hear him. He also had an ataxic gait with frequent falls, no loss of consciousness. In addition there was increased tremor. I know what you're thinking, but he denies alcohol and it was negative (besides, that would be too easy). He denied any dizziness, dyspnea, chest pain, nausea, vomiting, or diarrhea.

Vital signs showed bradycardia. His exam was notable for restricted affect, hypophonia, and one-word answers. He seemed to have difficulty finding words, almost an aphasia. He was alert and oriented. Cranial nerves were grossly normal, though I couldn't get him to follow commands. Sensation and motor was grossly normal. He was hyperreflexic throughout with clonus. Head, ears, eyes, nose, throat were normal. Lungs were clear. Cardiac was simply a bradycardia. There was some abdominal tenderness to deep palpation, but otherwise the belly was benign. There was no edema. He did have a tremor, mostly intention.

EKG showed a bradycardia that was mostly 1st degree heart block, but occasionally on telemetry, I spotted third degree AV dissociation. Head CT was negative. Labs were notable for Cr of 1.6, but otherwise lytes, CBC, LFTs, TFTs were normal.

I knew I couldn't finish wards without dodging a neurology case. What do you think it is?