Hashimoto's encephalopathy mimicking Creutzfeldt-Jakob disease

Hashimoto's encephalopathy is a rare, imprecisely defined autoimmune neurologic syndrome associated with Hashimoto's thyroiditis that normally responds to corticosteroids. Here, we describe the case of a 55-year-old woman who presented with subacute cognitive decline and ataxia. Neoplastic, paraneoplastic, infectious, and metabolic etiologies were ruled out. Anti-TPO antibody level was markedly elevated at 966U/mL. After one month of 60mg/day of oral prednisone, she felt back to baseline and her Montreal Cognitive Assessment dramatically improved. Physicians should strongly consider this uncommon diagnosis in patients with rapid cognitive decline and no other clear etiology.