Prediction of remission in Graves' disease treated with long-term carbimazole therapy: evaluation of technetium-99m thyroid uptake and TSH concentrations as prognostic indicators.

Computerized technetium-99m thyroid uptake and thyrotropin (TSH) estimation using a sensitive immunoradiometric assay were performed at presentation and following completion of an 18-month course of antithyroid drug therapy in 45 patients with Graves disease. All patients had increased 99mTc thyroid uptake and subnormal TSH levels before the start of treatment. Twenty-two patients developed recurrent hyperthyroidism in a 3-year follow-up period. Of these 22 patients with relapse, 20 had had a persistently increased 99mTc thyroid uptake at the end of the course of carbimazole treatment, whereas TSH had remained subnormal in 18 of the 22. All 23 patients who remained in remission until the end of the 3-year follow-up had had normal 99mTc thyroid uptake following completion of antithyroid drug treatment. TSH levels had reverted to normal in 19 cases, but remained subnormal in four cases in this group at the end of treatment. The results suggest a high likelihood of relapse in patients who have persistently increased 99mTc thyroid uptake and subnormal TSH after a full course of carbimazole treatment. Patients whose 99mTc thyroid uptake and TSH levels have reverted to normal are likely to stay in long-term remission. Assessment of 99mTc thyroid uptake and TSH levels following completion of carbimazole therapy for Graves disease offers useful information regarding long-term prognosis.