Steroid-Responsive Epilepsia Partialis Continua with Anti-Thyroid Antibodies: A Spectrum of Hashimoto's Encephalopathy?

BACKGROUND: When a neuropsychiatric symptom due to encephalopathy develops in a patient with anti-thyroid antibodies, especially when the symptom is steroid-responsive, Hashimoto's encephalopathy (HE) needs to be included in the differential diagnosis of the patient. Although HE is an elusive disease, it is thought to cause various clinical presentations including seizures, myoclonus, and epilepsia partialis continua (EPC). CASE REPORT: We present the case of a 33-year-old Japanese woman who acutely developed EPC in the right hand as an isolated manifestation. A thyroid ultrasound showed an enlarged hypoechogenic gland, and a thyroid status assessment showed euthyroid with high titers of thyroid antibodies. A brain MRI revealed a nodular lesion in the left precentral gyrus. Corticosteroid treatment resulted in a cessation of the symptom. CONCLUSIONS: A precentral nodular lesion can be responsible for steroid-responsive EPC in a patient with anti-thyroid antibodies and may be caused by HE. The serial MRI findings of our case suggest the presence of primary demyelination, with ischemia possibly due to vasculitis around the demyelinating lesion.