A 76-year-old man is brought to the physician by his son for unsteadiness and several near-falls over the last 2 weeks. The patient has been less interactive lately and prefers to stay in his room. His symptoms have been slowly worsening over the last 2 weeks. He has had no recent illness, fever, chills, or headaches. His medical problems include mild dementia, ischemic stroke without significant residual deficit, and seizure disorder. His medications include aspirin, phenytoin, levetiracetam, and vitamin D. He was recently started on omeprazole for reflux symptoms.
The patient's vital signs are within normal limits. Physical examination shows a narrow-based, unsteady gait with poor balance. His speech is slightly slurred. The patient has horizontal nystagmus and poor coordination with rapid alternating movements and finger-to-nose maneuvers bilaterally. His strength and sensation are intact.
Which of the following is the most likely diagnosis?

Question

A 76-year-old man is brought to the physician by his son for unsteadiness and several near-falls over the last 2 weeks.  The patient has been less interactive lately and prefers to stay in his room.  His symptoms have been slowly worsening over the last 2 weeks.  He has had no recent illness, fever, chills, or headaches.  His medical problems include mild dementia, ischemic stroke without significant residual deficit, and seizure disorder.  His medications include aspirin, phenytoin, levetiracetam, and vitamin D.  He was recently started on omeprazole for reflux symptoms.
The patient's vital signs are within normal limits.  Physical examination shows a narrow-based, unsteady gait with poor balance.  His speech is slightly slurred.  The patient has horizontal nystagmus and poor coordination with rapid alternating movements and finger-to-nose maneuvers bilaterally.  His strength and sensation are intact.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec193a_9888_ea38_853d_a1d16cbef1d5_MD0002_00 This patient's presentation suggests phenytoin toxicity. Early signs of toxicity include horizontal nystagmus and gait unsteadiness. These may be followed by slurred speech, lethargy, confusion, or even coma. Bradyarrhythmias and hypotension are usually seen with intravenous phenytoin. Toxicity can occur after dosage increase, with drug-drug interactions causing altered metabolism, hepatic or renal disease, or decreased serum albumin. This patient recently started omeprazole, which inhibits cytochrome P450 and leads to increased serum phenytoin levels. However, increased levels are not seen with other proton pump inhibitors (eg, dexlansoprazole, esomeprazole, lansoprazole, pantoprazole, rabeprazole). Hypoalbuminemia results in higher free phenytoin levels that lead to toxicity even when total phenytoin levels are not significantly elevated. Most cases of phenytoin toxicity are managed with supportive care. (Choice A) Benign positional paroxysmal vertigo (BPPV) usually presents with recurrent attacks of vertigo lasting < 1 minute and provoked by head movements. The Dix-Hallpike maneuver can usually provoke vertigo and nystagmus to confirm the diagnosis of posterior canal benign positional paroxysmal vertigo. Dix-Hallpike maneuver (Choice B) Symptoms of cerebellar stroke are usually acute in onset and include headache, vertigo, nystagmus, vomiting, wide-based gait, and ataxia. This patient's clinical presentation and duration of symptoms make cerebellar stroke less likely. (Choice C) Depression often goes undetected in elderly patients but does not usually cause nystagmus, slurred speech, or the other clinical findings seen in this patient. (Choice E) Vitamin B12 deficiency presents with macrocytic anemia, cognitive defects, and symmetric peripheral neuropathy. Patients may complain of paresthesias and loss of vibratory and positional senses. In severe cases, it can lead to severe weakness, fecal and urinary incontinence, and paraplegia. Educational objective: Phenytoin toxicity presents with horizontal nystagmus, ataxia, slurred speech, and mental status changes. Causes include dosage increase, drug-drug interactions causing altered metabolism, hepatic or renal disease, or decreased serum albumin. Treatment includes discontinuation of the drug and supportive care. __________ References: Phenytoin poisoning. (http://www.ncbi.nlm.nih.gov/pubmed/16174888)

A 76-Year-Old Man Is Brought to the Physician by His