Clinical Reasoning: A 54-year-old woman with dementia, myoclonus, and ataxia

A 54-year-old woman was referred for a second opinion regarding a 3-month history of subacute onset progressive cognitive decline. She complained of memory difficulties particularly with short term recall. Decision-making and organizational skills were increasingly difficult. She also developed sudden brief jerking movements of her body and progressive gait imbalance and incoordination leading to falls. Three months after onset, she could not work, drive, cook, or perform activities of daily living. She had not had episodes suggestive of seizures. Her medical history was remarkable for celiac disease diagnosed 9 years previously, which resolved with a gluten-free diet, collagenous colitis, Raynaud syndrome, osteopenia, anxiety, and prior episodes of hyponatremia related to polydipsia. Current medications included amitriptyline, venlafaxine, and Pepto-Bismol. She worked as a financial analyst, had never consumed tobacco products, and drank 3-4 alcoholic beverages per week. Her father had myasthenia gravis but there was no family history of dementia. General examination revealed a restless woman with pseudobulbar affect who was unable to provide a meaningful history. Neurologic examination revealed multiple abnormalities. Mental status testing revealed a mild to moderate degree of encephalopathy including abnormalities in attention, frontal lobe function, and comprehension. Kokmen short test of mental status score was 23 out of 38 (29/38 or less consistent with dementia). There was multifocal myoclonus and postural tremor. Cerebellar examination revealed appendicular and gait ataxia. Muscle strength and reflexes were normal. Sensory examination was unreliable due to dementia.