Serum thyroglobulin after mantle irradiation for Hodgkin's disease

Thyroid function and serum thyroglobulin levels were studied in 66 subjects whose Hodgkin's disease had been previously treated by cervical, mediastinal and axillary lymph node (mantle) irradiation. Three patients were already undergoing treatment for thyroid disorders (one for primary hypothyroidism, two for Graves' disease) and a fourth was found to have euthyroid Graves' disease. 36 (Group I) of the remaining 62 patients had normal free thyroxine indices, normal basal thyrotrophin (TSH) levels and normal TSH response to thyrotrophin releasing factor (TRH). In 20 patients (Group II) free thyroxine indices were normal but either basal TSH levels were raised or normal basal TSH levels were associated with an exaggerated response to TRH. In 6 patients (Group III) free thyroxine indices were subnormal. Although results of thyroid function tests in group I lay within the normal range, the mean free thyroxine index was significantly lower and mean basal and peak TSH levels were significantly higher than those of a group of 35 normal subjects, indicating mild thyroid hypofunction. Elevated thyroglobulin levels were demonstrated in 11 irradiated subjects (18%). Mean thyroglobulin levels were significantly raised in each of the three groups of irradiated subjects. Significant positive correlations were found between log serum thyroglobulin and log basal TSH (r = 0.453, P less than 0.001) and log peak TSH (r = 0.515, P less than 0.001) levels. Mild thyroid hypofunction is common after mantle irradiation for Hodgkin's disease and raised serum thyroglobulin levels are a sensitive indicator of TSH stimulation of the damaged thyroid gland.