Predicting relapse of Graves' disease following treatment with antithyroid drugs

The aim of the present study was to monitor long term antithyroid drug treatments and to identify prognostic factors for Graves' disease (GD). A total of 306 patients with GD who were referred to the Endocrinology Clinic at Weifang People's Hospital (Weifang, China) between August 2005 and June 2009 and treated with methimazole were included in the present study. Following treatment, patients were divided into non-remission, including recurrence and constant treatment subgroups, and remission groups. Various prognosis factors were analyzed and compared, including: Patient age, gender, size of thyroid prior to and following treatment, thyroid hormone levels, disease relapse, hypothyroidism and drug side-effects, and states of thyrotropin suppression were observed at 3, 6 and 12 months post-treatment. Sixty-five patients (21.2%) were male, and 241 patients (78.8%) were female. The mean age was 42 +/- 11 years, and the follow-up was 31.5 +/- 6.8 months. Following long-term treatment, 141 patients (46%) demonstrated remission of hyperthyroidism with a mean duration of 18.7 +/- 1.9 months. The average age at diagnosis was 45.6 +/- 10.3 years in the remission group, as compared with 36.4 +/- 8.8 years in the non-remission group (t=3.152; P=0.002). Free thyroxine (FT) 3 levels were demonstrated to be 25.2 +/- 8.9 and 18.7 +/- 9.4 pmol/l in the non-remission and remission groups, respectively (t=3.326, P=0.001). The FT3/FT4 ratio and thyrotrophin receptor antibody (TRAb) levels were both significantly higher in the non-remission group (t=3.331, 3.389, P=0.001), as compared with the remission group. Logistic regression analysis demonstrated that elevated thyroid size, FT3/FT4 ratio and TRAb at diagnosis were associated with poor outcomes. The ratio of continued thyrotropin suppression in the recurrent subgroup was significantly increased, as compared with the remission group (P=0.001), as thyroid function reached euthyroid state at 3, 6 and 12 months post-treatment. Patients with GD exhibiting large thyroids, high pre-mediation TRAb levels and elevated FT3/FT4 ratios responded less markedly to antithyroid drug treatments, as compared with patients not exhibiting these prognostic factors. Furthermore, patients with large thyroids, post-medication ophthalmopathy and continued thyrotropin suppression demonstrated higher rates of recurrence.