Several studies were done investigating thyroid function in patients with epilepsy. However the results of different studies were conflicting or controversial. This study aimed to evaluate thyroid hormonal changes and their relationship to thyroid volume in epileptic adults on long-term treatment with antiepileptic drugs (AEDs). This study included 135 adults with idiopathic epilepsy with mean age of 32.32پ}4.34years, duration of illness of 10.52پ}5.08 years and on treatment with carbamazepine (CBZ), valproate (VPA) or CBZ+VPA for a mean duration of 8.66پ}3.32years. The serum levels of free thyroxine (fT4), triiodothyronine (fT3), and thyroid-stimulating hormone (TSH) were assessed. Thyroid volume was measured using ultrasonography.
Compared to control subjects, patients had significant lower fT4 (p<0.01) and fT3 (p<0.01) and higher levels of TSH (p<0.0001). The majority of patients with reduced fT4 also had reduced fT3 and increased TSH levels. Nearly 26% of the patients had enlargement of the thyroid gland (p<0.001). Patients on polytherapy had more thyroid volume compared to patients on monotherapy (p<0.05) and patients on VPA had more thyroid volume compared to patients on CBZ (p<0.03). All patients were clinically euthyroid. Significant correlations were identified between fT4 concentrations and duration of illness, dose, serum level and duration of AEDs treatment, fT3 and TSH concentrations and between thyroid volume and fT4, fT3 and TSH concentrations. In conclusion, CBZ and VPA as mono- or polytherapies may cause thyroid hormonal and structural abnormalities. Thyroid enlargement is due to associated subclinical hypothyroidsm. This data have implications suggesting prevention strategies.

Abbreviations: AEDs, Antiepileptic drugs; CBZ, carbamazepine; VPA, valproate; fT3, free triiodothyronine; fT4, free thyroxine; TSH, thyroid stimulating hormone; SCH, subclinical hypothyroidism