Sudden-onset Encephalopathy: Do not ignore the Possibility of Hashimoto's Encephalopathy.

Hashimoto's encephalopathy (HE) is an uncommon neurological disorder of unknown etiology, found in association with thyroid autoimmunity, mostly uncommon in males. The disease occurs primarily in the fifth decade of life and may occur in two forms; a sudden vasculitic type or a progressive subacute type associated with cognitive dysfunction, confusion, and memory loss. We report a case of a 51-year-old Sri Lankan gentleman with no comorbidities who was presented with one episode of the generalized tonic- clonic seizure (GTCs) followed by prolonged agitation and disorientation. His EEG showed generalized slowing while CT scan and MRI brain were unremarkable. CSF examination showed high protein level with normal cell count and glucose. Routine serologic examination showed very high thyroid-stimulating hormone (TSH) level, with significantly high antithyroid antibodies. He was diagnosed as a case of Hashimoto's encephalopathy and treated with a high dose of steroid and showed remarkable improvement.