Hashimoto's Encephalopathy Masquerading as Rapidly Progressive Dementia and Extrapyramidal Failure.

Hashimoto's encephalopathy is a rare immune-mediated disorder characterized by subacute encephalopathy with elevated thyroid antibodies. Hashimoto's encephalopathy is also known as steroid-responsive encephalopathy associated with autoimmune thyroiditis. We report a rare presentation of Hashimoto's encephalopathy presenting with acute neuropsychiatric disturbances, rapidly progressive dementia, seizures, and extrapyramidal failure. Neuroimaging revealed multifocal vasculitides of major cerebral vessels that support the autoimmune vasculitic theory as the underlying pathogenesis for Hashimoto's encephalopathy. Unfortunately, permanent irreversible cerebral damage has already ensued before her presentation to our center, which rendered steroid therapy ineffective. Serological testing for Hashimoto's thyroiditis must be in the investigation of all rapidly progressive dementias as early diagnosis and timely management of autoimmune thyroiditis may salvage sizable and eloquent cerebral tissues. The rarity of the condition should not preclude the investigation of Hashimoto's disease even in the presence of normal levels of thyroid hormones. Delayed diagnosis may result in irreversibly catastrophic encephalopathy in patients who once presented with potentially curable dementia.