Summary:Purpose: The aim of this study was to evaluate the effects of short-term oxcarbazepine (OXC) and valproate (VPA) monotherapy on thyroid functions in children.Methods: Fifty-five newly diagnosed epileptic children with normal thyroid functions (confirmed with the thyrotropin releasing hormone stimulation test) participated in this study. VPA treatment was started in 30 patients and OXC in 25 patients. Serum thyroxine (T 4 ), free thyroxine (fT 4 ), triiodothyronine (T 3 ), free triiodothyronine (fT 3 ), reverse T3 (rT 3 ), thyroid peroxidase antibodies (TPO-ab), and urine iodine levels were evaluated at baseline and at the third and sixth months of therapy.Results: In the OXC group, serum T 4 , fT 4 , T 3 , fT 3 , and rT 3 levels were found to be decreased at the third and sixth months, the differences were significant compared to the baseline values except for fT 3 levels at the third month and fT 4 and rT 3 levels at the sixth month (p < 0.05). At the sixth month, serum T 4 level dropped below the normal reference value in 8 (32%), fT 4 in 5 (20%), T 3 in 4 (16%), and fT 3 in 3 (12%) patients. In the VPA group, mean T 4 , fT 4 , T 3 , fT 3 , and rT 3 levels at 3 and 6 months remained similar compared to the baseline values (p > 0.05). Mean serum thyroid stimulating hormone levels increased significantly at the sixth month compared to the baseline values in the VPA group (p < 0.05) while it remained unchanged in the OXC group (p > 0.05). There was no effect of either drug on urinary iodine excretion and serum TPO-ab levels remained in normal ranges throughout the study.Conclusions: In this prospective study, it is documented that children under short-term OXC or VPA therapy showed altered thyroid functions similar to the changes observed after long-term treatment. Although, the clinical significance of these results need to be evaluated with future studies, this observation of altered thyroid functions points out that thyroid functions may need to be monitored closely in children receiving antiepileptic treatment, even in the short-time interval.

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Thyroid function should be evaluated periodically in children using CBZ, OXC or VPA. The children taking VPA seems to be at greater risk compared to children onr CBZ or OXC therapy. Except for the basal TSH values in the VPA group, the parameters predictive for the subclinical hypothyroid status remain to be evaluated in further studies.

To our knowledge, this is the first pediatric study evaluating seizure outcome over more than 5 years of follow-up, and demonstrates a favorable seizure outcome of >50 % seizure frequency in 62.5 % of patients and seizure freedom in 11 patients. It is well tolerated over an extended period of time.

The most important risk factors for epilepsy in this study were neurological impairment, history of atypical febrile seizures, severe head injury and a low apgar score. Other important risk factors were moderate head trauma and a history of epilepsy in the family.