Seizure threshold in juvenile myoclonic epilepsy with Graves disease.

Thyroxine lowers the seizure threshold in experimental animals and humans. We report juvenile myoclonic epilepsy (JME) in two female patients with Graves' disease who had exophthalmos at age 11 (patient 1) and age 12 years (patient 2) but remained untreated until onset of seizures at ages 15 and 13 years, respectively. Seizures were not controlled well despite administration of antiepileptic drugs (AEDs) during the periods of excess serum thyroid hormones in Graves disease. When the serum levels of T3 were reduced to < 220 ng/dl with antithyroid drug treatment, both clinical seizures and paroxysmal EEG abnormalities disappeared despite discontinuation of AEDs and sleep deprivation. JME was noted only during periods of excess thyroid hormone and low compliance with antithyroid drug treatment. The excessively high level of thyroid hormones may have been a factor in precipitating the onset of JME.