Primary hypothyroidism and the low T3 syndrome in thalassaemia major

Abstract

SUMMARY Basal thyroid function was assessed from the serum thyroxine, triiodothyronine, and thyroid-stimulating hormone concentrations in 1 14 patients (mean age 13 * 6 years), designated group 1, with thalassaemia major. Forty of these patients were further evaluated (group 2) for serum-free thyroxine, and free and reverse triiodothyronine concentrations. The response of thyroid-stimulating hormone to thyrotrophin-releasing hormone was measured in 25 patients from this subgroup. Results were compared with those from 53 control subjects. Primary hypothyroidism, defined by a raised thyroid-stimulating hormone level above the upper range limit of 6 5 VdU/ml of the controls, was present in 17 5 % of the 114 patients. In group 2 patients, a spectrum of thyroid disease spanning uncompensated and compensated primary hypothyroidism and decreased thyroid reserve was evident. The presence of primary hypothyroidism (uncompensated and compensated) was associated with an age of at least 10 years, an increased incidence of iron toxicity-related systemic complications, and an increased transfusion iron load, but not with an increased serum ferritin level. In the total 114 patients there were 9 who had the low triiodothyronine (sick euthyroid) syndrome. Primary hypothyroidism occurs in a significant proportion of thalassaemia major patients in the absence of obvious clinical signs of hypothyroidism; the low triiodothyronine syndrome associated with non-thyroidal disease is not uncommon.

A Review of Endocrine Disorders in Thalassaemia

“…This is contrary to previous studies [71,72] including a 12-year longitudinal study by Filosa et al [72] 7 years earlier which showed no association between ferritin levels or transfusion statuswith worsening thyroid function. Some studies have reported a high prevalence of primary hypothyroidism reaching up to 17% -18% [7,73] whereas others have reported a low prevalence of 0% -9% [74,75]. Shamshirsaz et al [1] demonstrated a prevalence of 7.7% in their study similar to the Italian study group [35] who found 6.2% patients to be hypothyroid where as Aydinok et al [47] showed the prevalence to be higher at 16%.…”

“…It usually occurs in severely anaemic and/or iron overload thalassaemics but is uncommon in optimally treated patients [7,65]. The pathogenesis is again unclear but thought to relate to lipid perioxdiation, free radical release and oxidative stress [65].…”

“…Endocrinopathies are now amongst the common complications of thalassaemia but determining the exact prevalence is difficult because of differences in age of first exposure to chelation therapy and the continuing improvement in survival in well-chelated patients [4]. Thus, data regarding the prevalence of endocrine dysfunction in patients with ß thalassaemia major are limited and often depend on compliance with treatment [5][6][7][8].…”

Correlation of Thyroid Hormone Derangement with Serum Ferritin Level in Children with Beta Thalassaemia Major at a Tertiary Care Hospital of Bangladesh

“…Beside various causes, iron overload is an important, although rare etiological factor in thyroid failure 13,14 . The thyroid gland function in thalassaemia major has been reported to be normal, decreased reserve, or primary hypothyroidism.…”

Growth and Puberty and Its Management in Thalassaemia

“…This endocrine complication is common in patients who are anaemic and/or poorly chelated (17%) but is rare in patients who are well treated [16]. Three types of thyroid dysfunction have been recognised: preclinical – the classical symptoms of hypothyroidism are absent; the serum FT4 is normal; TSH marginally increased and TSH response to TRH is increased; mild hypothyroidism growth retardation, tiredness and dry skin may be present, serum FT4 is marginally low whilst TSH is elevated and the TSH response to TRH is exaggerated.…”