Assessment of thyroid function during and after treatment of thyrotoxicosis.

Destructive therapy for thyrotoxicosis frequently results in hypothyroidism, necessitating life-long treatment with thyroxine. Antithyroid drug therapy is followed by remission in a considerable proportion of patients and subsequent clinical hypothyroidism is rare. There thus seems to be a strong case for the use of antithyroid drugs as the initial treatment in most thyrotoxic patients under the age of45 years. Beyond the age of 45 or 50 years the risk of cardiac problems increases. The plan of treatment proposed is an interim one based on data obtained in a prospective study of 105 patients followed for more than four years (Alexander, McLarty, Horton, and Pharmakiotis, 1973). Thyrotoxicosis followed one of three courses: remission after one course of antithyroid drugs (group 1, 43 patients, 41 %); persistent thyrotoxicosis (group 3, 43 patients, 41 %), in these patients either the disease was active more than four years after the start of antithyroid drug therapy (36 patients) or thyrotoxicosis had persisted for two to four years before subtotal thyroidectomy (seven patients); an intermediate group (group 2, 19 patients, 18%). We suggest, therefore, the use of antithyroid drugs in the majority of patients with Graves' disease under 45 years of age, coupled with repeated assessment of the response to treatment at sixmonthly intervals (Alexander et al, 1973; Goolden, Williams, and Thalassinos, 1973). Every six months a decision, based on clinical assessment together with evidence from the tests of thyroid function, is taken to follow one of three courses of action: to continue with antithyroid drugs, to arrange destructive therapy, or to stop antithyroid drugs if the disease has remitted. In many patients the disease will remit as shown by a return of normal thyroidal suppressibility. In order to assess the development of thyroidal suppressibility, triiodothyronine (T3) in a dose of 80 ,ug daily is given in conjunction with carbimazole. In the interim plan described below the choice of the form of destructive therapy (surgery or radioiodine) is assumed to follow conventional lines (Wayne, 1960; McGirr, 1972).