Thyroid and pituitary function following allogeneic bone marrow transplantation

Thyroid function was evaluated in 13 consecutive patients with chronic myelogenous leukemia to verify in allogeneic bone marrow transplantation if the fractionated irradiation protocol with low dose rate, previously applied to reduce the damage to various organs, also prevents the 43% incidence of primary hypothyroidism that occurs after the administration of single dose with higher dose rate. Following bone marrow transplantation, decreased plasma levels of total thyroxine and triiodothyronine and impaired response of thyrotropic cells to thyrotropin-releasing hormone were observed. These alterations reverted to normal in nine months and none of the patients was hypothyroid at the end of follow-up. The damage to thyrotropic cells appears to be selective because the secretion of prolactin was not impaired and that of gonadotropins even increased, as a consequence of gonadal failure. Longer follow-up is needed to determine if this irradiation protocol, which prevents the complication of permanent primary hypothyroidism and does not cause any destruction of thyroid cells, may increase the risk of irradiation-related thyroid tumors.