Combined l-thyroxine and l-triiodothyronine replacement therapy in congenital hypothyroidism

Abstract

Introduction: L-thyroxine replacement therapy is the treatment of choice for hypothyroidism. Recently, several studies suggested to complete it with l-triiodothyronine in acquired hypothyroidism. Aim: To study the role of combined l-thyroxine and l-triiodothyronine therapy in special cases with congenital hypothyroidism. Method: Data of 16 patients (age: 11.9±6.3 years; mean±SD) are presented who had high serum free thyroxine values or even above the upper limit of reference range (21.16±2.5 pmol/l) together with nonsuppressed TSH levels (15.7±5.7 mIU/l), and therefore received l-triiodothyronine in completion (0.18±0.09 μg/kg) once a day. Results: The combined replacement therapy resulted in a rapid improvement of the hormone parameters (TSH: 4.2±3.15 mIU/l; free thyroxine: 16.55±2.4 and free triiodothyronine: 7.4±1.8 pmol/l). The efficiency of this combined therapy proved to be more evident (TSH: 4.33±3.2 mIU/l; free thyroxine: 16.85±3.1 and free triiodothyronine: 6.4±0.85 pmol/l) in 10 patients treated for a longer period of time (duration of treatment: 2.9±2.0 years). The dose of thyroxine substitution decreased from 2.6±0.9 to 2.18±0.6 μg/kg/day), the ratio of these hormones was between 5:1 and 19:1 and the quotient of free fractions was normalized (3.8±0.4→2.6±0.3) during the replacement therapy. Conclusions: According to the observation of the authors a serious disturbance of feed-back mechanism may develop in some (>5%) children with congenital hypothyroidism (increased TSH release despite elevated free thyroxine level) after normal function of the feed-back system for years. Hormone parameters of these patients improve, then become normal on combined therapy supporting the rationale for this treatment method. Orv. Hetil., 2013, 154, 738–744.