Incidence of hypothyroidism after irradiation of the neck with special reference to lymphoma patients. A retrospective and prospective analysis.

Twenty-eight patients were studied prospectively in order to determine the incidence of hypothyroidism after mantle irradiation for malignant lymphoma. This group was compared with a historical group of 65 patients, among them 36 patients with malignant lymphoma. The mean follow-up was 30 months for the prospective group and 46 months for the retrospective group. The mean thyroid dose for irradiated malignant lymphomas in the prospective and the retrospective group was 45 Gy and 43 Gy respectively. For other tumors with neck irradiation (retrospective group) the mean thyroid dose was 53 Gy. There were no cases of clinical hypothyroidism in our study. As for subclinical hypothyroidism which is characterised by elevated TSH, the incidence was 22% in the prospective group and 3% in the retrospective group, i.e. 8/93 patients showed a hypothyroid dysfunction. Three of the 8 patients with subclinical hypothyroidism had undergone lymphangiography before radiotherapy. Due to the elevated iodine pool a lymphangiogram is considered as a risk factor for hypothyroidism as well as for hyperthyroidism, which we observed twice in the prospective group. Evaluation of the thyroid function before lymphangiography and irradiation as well as regular thyroid function studies during the follow-up are recommended in order to detect hypothyroidism in time.