Hashimoto's encephalopathy: a rare pediatric brain disease.

We report a 9-year-old female who presented with new onset intractable seizure activity followed by a prolonged encephalopathic state. After ruling out common etiologies, Hashimoto's encephalopathy (HE) was considered, and antibody levels to thyroid peroxidase and thyroglobulin were both markedly elevated in her serum. She was euthyroid at the time of presentation. Upon treatment with high dose methylprednisolone, the patient demonstrated a significant improvement in her encephalopathy. The diagnosis of HE requires strong clinical suspicion with evidence of antithyroid antibodies, as well as an encephalopathy not explained by another etiology. While well documented in the adult literature, only a handful of pediatric cases have been described to date. Patients with HE have a nearly universal response to high dose glucocorticoids. HE should be considered in the differential diagnosis of any patient, adult or pediatric, who displays prolonged, unexplainable encephalopathy.