Endocrine Abstracts

The first treatment for hypothyroidism introduced at the end of the 19th century was animal thyroid extract which contained both T₃and T₄. Because of variable potency it was widely replaced by synthetic T₄ from the 1960s in high doses of 200-400 ug daily to compensate for the lack of T₃. The development of TSH assays showed that a dose of T₄ of 100-150 ug daily was usually adequate to restore serum TSH to normal. Because a suppressed serum TSH has been shown to be a risk factor for osteoporosis, atrial fibrillation, and most recently for excess cardiovascular mortality, there is a consensus that the correct treatment of hypothyroidism is a dose of thyroxine which restores euthyroidism and maintains both T₄ and TSH in their respective reference ranges. However, a significant minority of patients only achieve the desired sense of well-being if serum TSH is suppressed. Furthermore, patients rendered hypothyroid following treatment of thyrotoxicosis and taking a dose of T₄ which maintains a normal TSH, gain more weight than those who do not become hypothyroid. Studies in hypothyroid rats suggest that it is only possible to restore universal tissue euthyroidism using a combination of T₃and T₄. In patients in whom long-term T₄ therapy was substituted by the equivalent combination of T₃ and T₄ scored better in a variety of neuropsychological tests. It would appear that the treatment of hypothyroidism is about to come full circle.