Graves' disease: evolution and prognosis after eight months of treatment with methimazole

We studied 26 patients with Graves' disease, from a population with sufficient iodine supply, treated with high doses of methyl mercaptoimidazole (MMI) during eight moths. We evaluated: a) their evolution after treatment withdrawal; b) the correlation between evolution and TSH-receptor antibodies (TRAb), thyroid hormone levels, microsomal antibodies (MAb), T3/T4 index and clinical data; c) their prognosis. The patients were followed during 12-60 months, and blood samples were collected before treatment withdrawal. Out of 26 patients, 20 relapsed, with T3/T4 index and TRAb significantly higher than those under remission. The T3/T4 index correlated with TRAb. All the TRAb-positive patients, and only 57.1% of the negatives, relapsed. The relapses were significantly more frequent prior to the 6th month in the TRAb-positive patients than afterwards. The TRAb-negatives who relapsed during that period, showed TRAb and age means significantly higher than those under remission. The TRAb test, as a prognostic marker of evolution, showed a sensitivity of 60% and a specificity of 100%. No significant differences were found between evolution to relapse or to remission and the other parameters. It can be concluded that TRAb and T3/T4 index were different in the group that relapsed from that which remitted, and that a TRAb positive value, at the moment of treatment withdrawal, is a useful marker of relapse.