An unusual presentation of Hashimoto's encephalopathy.

Hashimoto's encephalopathy (HE) is a rare steroid-responsive encephalopathy syndrome, which can have highly variable neuropsychiatric manifestations and can go unrecognized for a long time. HE is a diagnosis of exclusion and should be kept in mind when evaluating a patient with a cognitive dysfunction and high titers of anti-thyroid antibodies as it responds dramatically to steroids. Steroid responsive myoclonus can be a presentation of HE.