Thyroid dysfunction following external irradiation to the neck for Hodgkin's disease in childhood

Thyroid function was studied in 32 patients who had received neck irradiation during childhood for Hodgkin's disease. All except one patient received a dose of 2500-3000 rad over a period of 19-25 days. In 12 patients lymphangiography was performed. Clinically all patients were considered euthyroid. One had a thyroid swelling which was cystic in nature. Five (16%) patients were biochemically hypothyroid, 17 (53%) were euthyroid with an elevated basal serum TSH concentration and a further seven (22%) were euthyroid with a normal basal serum TSH level but an augmented thyroid-stimulating hormone (TSH) response to thyrotrophin-releasing hormone (TRH). Only three (9%) patients had completely normal thyroid function tests. The basal serum TSH concentration and the peak serum TSH response to TRH were significantly greater in the patients who received neck irradiation and lymphangiography than in those who received neck irradiation alone. In addition the free thyroxine index decreased significantly as the time interval between treatment and study increased in the lymphangiography group. These data demonstrate that the normal thyroid gland is vulnerable to the damaging effects of external irradiation, and that the combination of neck irradiation and lymphangiography is more likely to result in thyroid dysfunction than is neck irradiation alone. Furthermore, in view of the deterioration in thyroid function with time, periodic clinical and biochemical assessment of thyroid function is clearly indicated.