Thyroid peroxidase autoantibodies are associated with a lesser likelihood of late reversion to hyperthyroidism after successful non-ablative treatment of Graves’ disease in Croatian patients

Background Thyroid peroxidase autoantibodies (TPOAbs) are frequently observed in Graves’ disease (GD) and tend to persist in patients even after successful treatment with antithyroid drugs. However, there is a lack of consistent data regarding the prognostic significance of TPOAbs during and after non-ablative treatment for Graves’ hyperthyroidism. Aim To assess the prognostic value of TPOAbs on the long-term outcome of GD patients, who were in remission after the use of antithyroid drugs (block-and-replace regimen). Subjects 100 remitters were retrospectively investigated for factors associated with the 5-year course of disease recurrence and compared to 60 age/sex-matched patients with intractable GD. Results Mild hyperthyroidism, low baseline thyroid-stimulating antibodies levels, and small goiters were predictive of remission. Once attained, the remission was shorter in younger patients, patients with declining post-treatment TSH values, and negative baseline TPOAb levels. The 5-year cumulative incidence of relapse incrementally increased from 24 to 44 to 70 % across decreasing TPOAb tertiles (log-rank, p = 0.00056; the lower tertile representing TPOAb-negative cases). The age-of-onset ( p = 0.034), and the baseline TPOAb value [upper tertile, hazard ratio (HR) 0.25; 95 % confidence interval, 0.11–0.59; p = 0.0014; middle tertile, HR 0.47 (0.24–0.9); p = 0.024; Cox regression] were inversely associated with late (>12 months) relapse rates in a level-dependent manner. In contrast, serum logTSH measured 6 months after drug discontinuation was inversely associated with hazard rates at all time points ( p = 0.0005). Conclusion Baseline TPOAb positivity is an independent indicator of long-term remission in GD patients who have been successfully treated, but the mechanism of action and causal relations remain unknown.