Impact of antiseizure medications on thyroid function in persons with epilepsy

Antiseizure medications (ASMs) are central to epilepsy management but may disrupt endocrine function, particularly thyroid homeostasis. Subclinical and central hypothyroidism are increasingly recognized among ASM users, yet routine thyroid monitoring remains uncommon.

To evaluate the prevalence and patterns of thyroid dysfunction in epilepsy patients on ASMs and compare the impact of older versus newer ASMs on thyroid function.

This cross-sectional study included 203 patients with epilepsy admitted to a tertiary epilepsy care centre in South India between July 2013 and March 2014. Patients with known thyroid disorders or other conditions affecting thyroid function were excluded. Thyroid function tests (TSH, fT3, fT4) were performed. Subclinical hypothyroidism was defined as elevated TSH with normal fT3/fT4; central hypothyroidism as low fT3/fT4 with normal or low TSH. ASMs were categorized into older and newer groups. Data were analysed using SPSS with appropriate parametric and non-parametric methods.

Subclinical hypothyroidism was found in 11.3% of patients, more common in generalized epilepsy (56.5%) than focal epilepsy (43.5%) (p = 0.005). Valproate and clonazepam were most frequently associated. Among patients on monotherapy, none on newer ASMs had subclinical hypothyroidism, whereas 14.9% on older ASMs were affected (p = 0.35). Central hypothyroidism occurred in 10.3%, predominantly among users of zonisamide, phenobarbital, oxcarbazepine, and clobazam. Both older and newer ASM groups showed similar central hypothyroidism rates (9.6% versus 9.1%) CONCLUSION: Both older and newer ASMs exert clinically significant effects on thyroid homeostasis. Older ASMs were more often linked to subclinical hypothyroidism, while central hypothyroidism risk was comparable across ASM types. Annual thyroid screening is recommended to detect dysfunction early and prevent metabolic and cardiovascular complications.