A central hypothyroidism induced by oxcarbazepine therapy

Antiepileptic drugs lead to various degrees of impairment in thyroid hormone homeostasis. In general, slightly low thyroxine (T4) and elevated thyroid stimulating hormone (TSH) levels have been reported because induced hepatic enzymes contribute to the clearance of thyroid hormone. On the other hand, it was thought that oxcarbazepine (OXC) could suppress the hypothalamus-pituitary axis, resulting in the decreased responsiveness of thyrotropin-releasing hormone-thyrotropin. A twelve-year-old girl began OXC therapy after she was diagnosed with complex partial epilepsy. She had normal thyroid function before OXC therapy, which was verified when she took a thyroid function test due to fatigue 1 year prior. Eight months after taking OXC, the levels of free T4 and TSH were 0.69 ng/dL and 1.42 mIU/L, respectively. The TSH level was inappropriately normal despite a reduction in the free T4 level, suggesting the presence of central hypothyroidism. She had been treated with 100 mcg of levo-thyroxine for approximately 3 years. Her thyroid function recovered after she ceased taking OXC medication. However, the levels of free T4 and TSH were 0.81 ng/dL and 1.25 mIU/L at a month after she resumed OXC medication due to recurred seizure. Thyroid function should be closely monitored in long-term OXC users and especially when we use antiepileptic drugs in patients with hypothyroidism or hypopituitarism.