Exaggerated TSH response to TRH ("sub-biochemical" hypothyroidism) in prepubertal and adolescent thalassaemic patients with iron overload: prevalence and 20-year natural history.

The severity of thyroid dysfunction in patients with beta-thalassaemia major is variable in different series. An exaggerated thyrotropin response to thyrotropin-releasing-hormone (TRH) has been found in 1 out of 5 beta-thalassaemia major patients. Because it is not well known how many of these patients will develop overt or subclinical hypothyroidism, we reviewed retrospectively the thyroid status (thyroid hormones, TBG, TG basal and TSH peak after TRH test) of 24 children and adolescents with beta-thalassemia major (mean age 12.1+/-3.9 years) on periodic transfusion therapy, regularly followed in our Centre during the last 20 years. As controls we studied 30 normal subjects aged 13.4+/-2.5 years. In our group of 24 thalassaemics an exaggerated TSH response to TRH test was found in 8 (33.3%), 3 of whom developed subclinical or overt hypothyroidism from 3 to 11 years later. TSH peak values correlated directly with ferritin levels, ALT, and compliance index to chelation therapy. Our data suggest that an exaggerated TSH response to TRH test is frequent in beta-thalassemia major, and may evolve into subclinical or overt hypothyroidism as we found in 37.5% of our patients with sub-biochemical hypothyroidism.