Background: Graves hyperthyroidism is treated with anti-thyroid drugs (ATD) for 1218 months, after which ~50% of patients remain euthyroid. Risk factors predicting relapse are: male gender, younger age, orbitopathy, large goitres, severe hyperthyroidism at diagnosis and smoking. Recent reports suggest measurement of TBII at ATD cessation is useful in predicting risk of relapse. Aim: To prospectively investigate whether TBII levels at cessation of ATD therapy are useful in predicting risk of relapse of Graves hyperthyroidism.
Methods: Consecutive patients with Graves hyperthyroidism (n=49) were treated with ATD for 1218 months. After cessation, patients were followed up to 18 months. At this point, patients were classed as relapse-free if serum TSH level ≥0.4 mU/L and relapsed if TSH ≤0.4 mU/L or had raised thyroid hormone levels. Age, gender, smoking habits, orbitopathy, duration of treatment with ATD, thyroid hormones and TBII at baseline and at ATD cessation were recorded. Binary logistic regression analysis was performed to predict the variables that best predicted relapse.
Results: At 18 months post ATD cessation, 27 (55%) patients were relapse-free and 22 (45%) had a relapse of hyperthyroidism. Baseline characteristics, duration of treatment, thyroid hormones and TBII levels at diagnosis were similar in both groups. At ATD cessation, TSH, FT4 and FT3 were similar in both groups, but TBII levels were significantly higher in the relapse group [median (range) of 3.2 (0.339.0)] than in the relapse-free patients [1.0 (0.53.8)], P<0.05. Multivariable analysis showed TBII levels at ATD cessation were the single best predictor of relapse. Furthermore, length of treatment with ATD was independently associated with change in TBII levels.
Conclusions: TBII levels at cessation of ATD therapy provide useful information about risk of relapse. Future research should investigate whether length of treatment should be individually tailored to degree of TBII reduction.
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.