A 12-year-old boy with Hashimoto encephalopathy and drug-resistant status epilepticus responsive to plasmapheresis is reported from Ankara University Medical School, Turkey. He was admitted with a right focal seizure, becoming secondary generalized tonic-clonic, refractory to treatment and necessitating a pentobarbital-induced coma. Recent history revealed a sudden change in personality, fever, headache, and fatigue, indicating limbic encephalitis. Serum anti-thyroid peroxidase antibody was elevated at 30 IU/ml (normal range, 0-9 IU/ml). Treatment with iv immunoglobulin was ineffective, and plasmapheresis was performed, followed by levothyroxine and oral prednisolone (2 mg/kg/day). The neurologic and psychiatric manifestations (orofacial dyskinesia, autonomic instability, emotional lability, and personality changes) decreased after the eighth plasmapheresis, and his examination was normal after 2 months. He was discharged taking prednisolone (1 mg/kg/day), levothyroxine, and antiepileptic drugs. 
COMMENT. Hashimoto encephalopathy (HE) is characterized by seizures, neurologic and psychiatric manifestations, and elevated titers of serum anti-thyroid antibodies. It is responsive to corticosteroids. Plasmapheresis is a novel method of acute treatment. HE should be considered, along with anti-N-methyl-D-aspartate-receptor, voltage-gated potassium channel antibody-associated limbic encephalitis, and herpes simplex virus encephalitis, in the differential diagnosis of a child with acute personality changes and seizures resistant to antiepileptic medication. The pathogenesis of HE is associated with high serum anti-thyroid antibody titers; thyroid hormone levels are usually normal or slightly low. An autoimmune disease process is likely.