Assessment of Thyroid Function in Two Hundred Patients with β -Thalassemia Major

Abstract

Despite improved hematologic care, multiendocrine dysfunction is a common complication of homozygous transfusion-dependent β-thalassemia. In this study our goal was to estimate the prevalence of thyroid dysfunction in a large homogenous group of thalassemic patients. Two hundred patients with β-thalassemia major (100 males and 100 females; mean age, 23.2 ± 6.7 years; age range 11-43 years), regularly transfused and desferioxamine chelated, were randomly selected from a pool of approximately 800 patients with β-thalassemia followed in our department. Thyroid function and iron-load status were evaluated by measurements of free thyroxine (FT₄), free triiodothyronine (FT₃), thyrotropin (TSH), and serum ferritin levels. Of the subgroup of patients who proved to have normal thyroid hormone values, 26 (12 males, 14 females; mean age, 23.6 ± 6.8 years; age range, 15-36 years) were randomly selected and underwent a standard TRH stimulation test. Thyroid dysfunction was defined as follows: overt hypothyroidism: low FT₄ and/or FT₃, increased TSH levels; subclinical hypothyroidism: normal FT₄, FT₃, increased TSH levels; exaggerated TSH response: normal FT₄, FT₃, normal basal TSH, ΔTSH ≥ 21 μIU/mL (TSH levels measured prior and 30 minutes after intravenous TRH administration). Normal thyroid hormone values were found in 167 (83.5%) of the 200 patients studied. Eight (4%) of the remaining patients had overt hypothyroidisim, and 25 (12.5%) had subclinical hypothyroidism. Exaggerated TSH response to TRH was revealed in 7 of the 26 patients with normal hormone values tested (26.9%). Antithyroglobulin and anti-thyroid peroxidase (TPO) antibody titers were negative in 191 patients(95.5%). Mean ferritin levels in hypothyroid and euthyroid patients were 2707.66 ± 1990.5 mg/L and 2902.9 ± 1997.3 mg/L, respectively, (p = 0.61), indicating no correlation between ferritin levels and thyroid functional status. Mean ferritin levels in the patients who responded normally to TRH stimulation and in those who overresponded, were 2586 ± 1791 mg/L and 3228 ± 2473 mg/L, respectively (p = 0.46; NS). Thyroid failure is a rather rare endocrine complication in patients with β-thalassemic from Greece. In our series, no case of central hypothyroidism was observed. No correlation was found between thyroid functional status and ferritin plasma levels. Approximately 1 of 5 β-thalassemic patients with normal thyroid hormone values showed an exaggerated TSH response to TRH test. It is to be investigated how many of these patients will establish overt or subclinical hypothyroidism in the future.