Thyrotrophin receptor antibody concentration and activity, several years after treatment for Graves' disease.

Abstract

TSH receptor antibodies (TRAb) are responsible for autoimmune hyperthyroid disease (Graves' disease; GD) with TRAb levels tending to decrease following treatment. Measurement of TRAb activity during follow-up could prove valuable to better understand treatment effectiveness. TRAb concentration and stimulating (TSAb) and blocking (TSBAb) activity of patient serum were assessed following different treatment modalities and follow-up length. Sixty-six subjects were recruited following treatment with carbimazole (n=26), radioiodine (n=27) or surgery (n=13). TRAb, TPOAb, TgAb and GADAb were measured at a follow-up visit as well as bioassays of TSAb and TSBAb activity. Forty-five per cent of all patients remained TRAb-positive for more than one year and 23% for more than 5years after diagnosis, irrespective of treatment method. Overall, TRAb concentration fell from a median (IQR) of 6.25 (3.9-12.7) to 0.65 (0.38-3.2) U/L. Surgery conferred the largest fall in TRAb concentration from 11.4 (6.7-29) to 0.58 (0.4-1.4) U/L. Seventy per cent of TRAb-positive patients were positive for TSAb, and one patient (3%) was positive for TSBAb. TRAb and TSAb correlated well (r=0.83). In addition, 38/66 patients were TgAb-positive, 47/66 were TPOAb-positive and 6/66 were GADAb-positive at follow-up. TRAb levels generally decreased after treatment but persisted for over 5years in some patients. TRAb activity was predominantly stimulatory, with only one patient demonstrating TSBAb. A large proportion of patients were TgAb/TPOAb-positive at follow-up. All treatment modalities reduced TRAb concentrations; however, surgery was most effective.