Endocrine Abstracts

Introduction: Antiepileptic drugs may cause altered thyroid function in adults according to previous studies. The cllinical impact of this is unclear. The aim of this study was to evaluate thyroid function in patients taking antiepileptic drugs to evaluate a possible clinical impact.

Methods: Adult epileptic patients (older than 18 years old) who attended the neurology outpatient clinic at Landspitali University Hospital in Iceland (the only University Hospital in the country) from 1st of January 1998 to 31st of December 2011 were included in the study. Patients were excluded if they had any previous history of thyroid disease and/or if they had been taking epileptic drugs for < 3 months. Information about medication, medical history and thyroid test results (serum free thyroxine (fT₄) and TSH) was gathered from medical reports. Patients were invited to undergo blood test if thyroid testing had not been done.

Results: 165 patients were included, 73 men and 92 women. The mean age was 45.6 (±15.5) years. The mean serum TSH was 2.2 (± 1.3) mIU/l, range <0.01 – 7.98 (reference value 0.30–4.20 mIU/l). The mean serum fT₄ concentration was 14.2 (±2.9) pmol/l, range 8.1–24.4 (reference value 12–22 pmol/l). Two patients had elevated TSH and low fT₄. Thirty-five patients had fT₄ below the reference range and normal TSH. Three patients had elevated fT₄ and a normal TSH. Twelve patients had elevated TSH and normal fT₄. Most patients found low in serum fT₄ and TSH levels complained of tiredness.

Conclusion: Low serum fT₄ is common in patients taking antiepileptic drugs and is not associated with TSH elevation, indicating central hypothyroidism. Further research is needed to determine whether thyroxine is an affective treatment in this patient population.