[A patient with Hashimoto's encephalopathy showing subacute global cognitive dysfunction].

We report a 66-year-old woman with Hashimoto's encephalopathy who showed rapidly developing cognitive deficits, inactivity, and gait disturbance without involuntary movements or convulsions. She had had right-sided hemiparesis and dysarthria caused by a lacunar infarction and had been admitted to our hospital for 2 weeks. Although the dysarthria and hemiparesis gradually improved, difficulty in walking, disorientation, and drowsiness developed 2 months after discharge. Upon readmission, the patient was alert but apathetic and sometimes sleepy. The right upper and lower limbs showed mild weakness, which was considered to be due to the previous infarction. Cerebrospinal fluid showed mild elevation of protein without pleocytosis. An electroencephalogram was normal, and a magnetic resonance imaging of the brain showed only the old lacunar infarction. Titers of antithyroglobulin antibodies and levels of thyroid stimulating hormone in serum were elevated. We made a diagnosis of Hashimoto's encephalopathy and treated the patient with high-dose corticosteroids. Within 1 week, her mental status improved and she was able to walk. Generalized seizure, myoclonus, and tremor, which are characteristic of Hashimoto's encephalopathy, never developed. The findings in this patient suggest that Hashimoto's encephalopathy, a treatable condition, should be included in the differential diagnosis of dementia.