Hyperthyroidism and hypothyroidism complicating the treatment of thyrotoxicosis.

Three separate studies of recurrent hyperthyroidism and hypothyroidism in groups of patients treated for thyrotoxicosis by anti-thyroid drugs, surgery and radioiodine are presented. The incidence is compared in the three groups. Two hundred and fifty-three patients with primary thyrotoxicosis received a year-long course of anti-thyroid drugs: 43 per cent relapsed in the first year following the completion of treatment. Of those remaining euthyroid at the beginning of the second year after treatment a further 21 per cent relapsed during that year and in subsequent years, 21 per cent, 18 per cent and 13 per cent of those remaining euthyroid at the start of the third, fourth and fifth years relapsed. Of those followed for the full 5 years 26 per cent remained in remission and 74 per cent had relapsed over this period. After bilateral subtotal thyroidectomy for thyrotoxicosis in 146 patients, 19 per cent were hypothyroid and 1.4 per cent had relapsed 18 months after surgery. The incidence of postoperative hypothyroidism was lower in the younger patients (under 25 years). The absence of thyroid auto-antibodies preoperatively is an indication of a favourable result. The histological recognition of lymphocytic infiltration in the gland and the presence of thyroid auto-antibodies indicated an unfavourable outcome. Radioactive iodine gave an unpredictable response at therapeutic doses with 24 per cent relapsing in the first year after treatment. With ablative doses of radioactive iodine the incidence of hypothyroidism reached 94 per cent at 5 years after treatment. Surgery gives the best long-term results of the three treatment options and is the treatment of choice for the young, the severely toxic and those with toxic multinodular goitre.