Introduction:
Epilepsy and epileptic syndromes are common in children. Frequent seizures have a great negative impact on the quality of life in children and their families, and many children with epilepsy need anticonvulsive therapy.

Aim of the study:
Despite reducing seizure frequency, anticonvulsive therapy has many complications. Subclinical hypothyroidism has been argued in children with epilepsy as a complication of anticonvulsive therapy and has been proposed as a risk factor for long-term cardiovascular problems. We aimed to determine the relative frequency of subclinical hypothyroidism in children with well-controlled epilepsy.

Material and methods:
In a prospective cohort, we assessed subclinical hypothyroidism in 228 children with epilepsy, who were treated with sodium valproate (n = 93), carbamazepine (n = 76), and phenobarbital (n = 59) as monotherapy and compared them with 100 age- and sex-matched healthy children as controls. We defined subclinical hypothyroidism as serum TSH level more than 3.8 µIU/ml and normal serum T4 level.

Results:
According to the definition, subclinical hypothyroidism was significantly more frequent in children with epilepsy than in healthy controls. Subclinical hypothyroidism was found in 25 (26.8%) children in the sodium valproate group, 15 (19.7%) in the carbamazepine group, and 13 (22%) in phenobarbital group, but only in four (4%) children in the control group.

Conclusions:
These results indicate that in children with epilepsy, who were treated by one of the following: carbamazepine, sodium valproate, or phenobarbital, as monotherapy, subclinical hypothyroidism could occur frequently. Monitoring of thyroid function using T4 and TSH serum level should be considered in these children during anticonvulsive therapy. However, long-term effects of anticonvulsive medications on thyroid function need well-designed, prolonged cohort studies.