Alterações tireoideanas em pacientes com beta-talassemia maior submetidos a hipertransfusão sanguinea




Among several clinical presentations of thalassemia syndromes, beta¬thalassemia major (Cooley s disease) is one of the great severity. The clinical features consist of chronic hemolytic anemia, from the early years of life, and severe hypoxia, requiring a regimen of chronic blood transfusions to survive. Treatment with chronic regular transfusions leads to iron overload, which is stored in the cells as ferritin. Chelation with desferrioxamine, generally subcutaneous, is used to minimize the effects of iron overload. Secondmy to severe hemolytic anemia, hypoxia and iron overload, several clinical features, as hepatomegaly, splenomegaly, typical skeletal manifestations (porotic hyperostosis and cortical defects due to bone marrow hyperplasia), endocrine dysfunctions (hypothyroidism, hypogonadism, insulin dependent diabetes mellitus) and cardiac failure are present. Chronic hepatic disease can be associated, due to iron overload and acquired viral infections that result from repeated transfusions. Sucessive improvement in the management of this disease and the new technologies increase quality and life expectancy. In our days these patients attain° growth, pubertal development and fertility similar to the general population. In order to determine the probable factors involved in thyroid dysfunction we studied a group of patients with beta-thalassemia major, in which the prevalence of hypothyroidism is 35%, greater than that reported in the literature.Our first hypothesis postulated the existence of specific beta-thalassemic alleles direct1y related to the clinical manifestations of primary hypothyroidism. However, the beta-thalassemic alleles present in our sample are similar to those described as the more frequent in São Paulo State, and no association was found with hypothyroidism. Significant differences between the groups of euthyroid and hypothyroid patients were observed: the latter were older, had smaller interval among transfusions, had great amount of transfusions, were older at the beginning of chelation therapy, had greater interval between the first transfusion and the beginning of the chelation therapy and had greater seric levels of ferritin and TSH and lower seric levels ofT3. Tissue damage could be the initial mechanism to induce hypothyroidism, due to iron deposition secondary to iron overload, then exposing cell antigens with late anti-thyroid antibodies formation. Since anti-thyroid antibodies are more frequent after forty five years of age, and more prevalent in females, we can not mle out the autoimmune aetiology as a possibility. On the other hand, the initial iron overload, before chelation therapy was initiated, could play a fundamental role in determining hypothyroidism, if we consider that the age at the beginning of chelation therapy can influence gonadal function and potencial fertitlity. It will be very interesting to observe the patients of the euthyroid group, as it attains the same mean age of the hypothyroid group, in order to evaluate if they will develop hypothyroidism in a similar frequency. It will be also possible to verify the influence of the delayed ons~t of chelating therapy


talassemia hipotireoidismo tereoide - doença

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