Optimal replacement therapy for autoimmune hypothyroidism

What is the optimal replacement therapy for autoimmune hypothyroidism? Thyroxine alone or thyroxine plus triiodothyronine?

Luigi Bartalena: This is a very good question. The main hormone produced by the thyroid is thyroxine, but most of thyroxine is then converted to the highly metabolically active hormone triiodothyronine (T₃). The thyroid produces also a small amount of T₃, but the optimal treatment for hypothyroidism is still represented by thyroxine (T₄).

However, a small proportion of patients, say 5% to 10%, are not happy with this replacement therapy and still complain of some symptoms that they had with untreated hypothyroidism. Therefore, it has been proposed that a combined treatment with T₄/T₃ might be more physiological and reproducing what happens in the normal thyroid. However, there has been a number of randomized clinical trials comparing thyroxine alone or thyroxine plus triiodothyronine and there is no clear evidence that the combined treatment is superior to the treatment with thyroxine alone. Therefore, the most recent guidelines indicate that replacement therapy, except for particular cases, should be performed using thyroxine alone.