Antiepileptic Drugs and Thyroid Hormone Homeostasis: Literature Review and Practical Guideline

Thyroid hormones play an essential role in central nervous system development, normal physiological brain function and repairing mechanisms. On one hand, thyroid hormone alterations influence cortical excitability and on the other hand anti-epileptic drugs (AEDs) are associated with alterations in thyroid hormone metabolism. Although this interaction has long been described, and epilepsy is a common and chronic neurological disease, studies describing the interplay are often small and retrospective. We performed a systematic review of the current literature on epilepsy, AED therapy and thyroid hormone metabolism. Forty-seven studies were included. Most studies were retrospective cross-sectional studies (n=25) and investigated thyroid function alterations in patients on older AEDs such as phenobarbital, phenytoin, carbamazepine and valproic acid. Overall, almost one third of patients with epilepsy had subclinical hypothyroidism, especially patients on valproate and carbamazepine. Studies with patients receiving polytherapy are scarce, but reported a higher risk for hypothyroidism in patients with older age, female sex, longer duration of epilepsy, intractable epilepsy and polytherapy. Studies on newer AEDs are also scarce and further studies essential to improve the care for epilepsy patients. AEDs are associated with alterations in thyroid hormone metabolism. Thyroid function monitoring is indicated in patients on AEDs, especially those with refractory chronic epilepsy and those on polytherapy. We provide a practical guideline for thyroid function monitoring for the clinician taking care of patients on AEDs.