Alterations in Serum Thyrotropin (TSH) and Thyroid Function Following Radiotherapy in Patients with Malignant Lymphoma1

Abstract

Seventy-seven of 174 patients (44%) with lymphomas who had lymphangiography and who received high-dose bilateral neck irradiation developed elevated serum TSH concentrations. Many of the elevations were recorded during the first post-treatment year. Elevated serum TSH values were observed with a higher frequency in treated patients under 20 yr of age. In untreated (X-irradiation) Hodgkin's disease, serum TSH levels were normal. Similarly, normal values were seen in patients whose field of irradiation did not include the neck. Nineteen patients developed radiation-induced pericarditis; 16 of the 19 had elevated serum TSH levels and 9 were clinically hypothyroid. Twenty-five patients (11%) developed clinical hypothyroidism and/or showed evidence of thyroid hypofunction by laboratory test other than serum TSH. The post-treatment incidence of abnormally high serum TSH levels was lower in a group of patients with tumors involving the neck region who received irradiation without prior lymphangiography, suggesting that an expanded extrathyroidal iodide pool may increase the susceptibility to hypothyroidism in the irradiated subject. The present data suggest that the concept of relative radioresistance of normal thyroid tissue should be revised. It is recommended that all patients undergoing high-dose bilateral neck irradiation for treatment of neoplasm be evaluated at least quarterly thereafter for laboratory and clinical evidence of hypothyroidism. Determination of immunoassayable serum TSH appears to be a sensitive means of detecting impaired thyroid function in such patients. The finding of an elevated serum TSH level is by itself probably sufficient evidence to indicate that thyroid dysfunction is present; prompt and adequate replacement thyroid therapy not only may give the patient great symptomatic relief, but may also resolve a question of recurrence or extension of the neoplastic process and/or forestall the development or lessen the severity of post-radiation pericarditis with effusion.