Opsoclonus as a manifestation of Hashimoto's encephalopathy.

We present a 59-year-old male with early manifestation of opsoclonus associated with gait ataxia as a rare clinical presentation of Hashimoto's encephalopathy. Empiric use of intravenous immunoglobulin followed by intravenous high dose methylprednisolone was initiated with subsequent remittance of opsoclonus, encephalopathy, ataxia, and tremor. Extensive workup for infectious, autoimmune, and paraneoplastic etiologies were undertaken and all studies were negative. Thyroglobulin antibodies (312 U/mL) and thyroid peroxidase antibodies (457 U/mL) were elevated (normal <60 U/mL) with a euthyroid state (thyroid stimulating hormone 3.13 μIU/mL). Three months after intravenous steroid therapy, the concentrations of thyroglobulin and thyroid peroxidase antibodies were retested and found to have decreased considerably. Thus, with steroid therapy, the patient's opsoclonus and encephalopathy improved. We have presented a patient with a rare case of opsoclonus as the principal presenting feature of Hashimoto's encephalopathy that was incompletely responsive to intravenous immunoglobulin and resolved with corticosteroids. This report underscores the importance for clinical practitioners to maintain a high index of suspicion for Hashimoto's encephalopathy in cases of opsoclonus, especially when accompanied by an atypical presentation.