Significance of thyroperoxidase and thyroglobulin antibodies in medically treated Graves' disease.

Background: Thyroperoxidase (TPOAb) and thyroglobulin (TgAb) antibodies are highly prevalent in Graves' disease (GD), but their significance is controversial. Methods: We retrospectively analyzed TPOAb and TgAb levels and evolution in 136 patients with newly diagnosed GD between 2000 and 2022, treated with anti-thyroid drugs (ATD) in a block-and-replace (B+R) regimen for at least 12 months and followed up for at least 1 year after ATD discontinuation or until disease relapse. Results: At diagnosis, 98 out of 136 (72%) patients were TPOAb positive and 73 out of 136 (54%) patients were TgAb positive. The presence of TPOAb or TgAb antibodies at diagnosis was generally not related to GD presentation and did not influence the risk of relapse (P = 0.304 and P = 0.348, respectively). There was less TED (thyroid eye disease) in TgAb-positive patients than TgAb-negative patients at diagnosis (11 out of 73 (15.1%) versus 21 out of 63 (33.3%) P = 0.012). In contrast, the presence of TPOAb at diagnosis was not associated with TED (P = 0.354). The absence of TgAb at diagnosis (P = 0.05) and time to euthyroidism (P = 0.009), but not smoking or TRAb levels, were associated with TED in multivariate logistic regression. TPOAb and TgAb levels during treatment and after its discontinuation were not predictive of relapse, except for lower titers of TgAb at 18 months in patients who relapsed (P = 0.034). Conclusion: In GD patients treated with a first course of ATD in a B+R regimen we observed lower titers of TgAb at the end of treatment in patients who relapsed and a significant protection against TED in patients with positive TgAb at diagnosis, irrespectively of TPOAb.