Prognostic Factors in the Relapse of Graves’ Disease Following Treatment with Antithy-roid Drugs

Background: Patients with Graves’ disease exhibit a considerable rate of relapse after treatment with antithyroid drugs and require ablative therapy. Objective: The purpose of this study was to evaluate variables which can be used as prognostic factors in predicting the outcome of Graves’ disease after treatment with antithyroid drugs. Methods: Age, sex, duration of antithyroid drug therapy, pretreatment T3 and T4 values, T3 to T4 ratio, size of thyroid gland before and after treatment, and the effect of salt iodination were determined in 439 patients at an endocrine clinic in southern Iran during a 15- year period.  The patients included 338 (77%) females and 101(23%) males with a mean age of 34.1±11.2 years. Results: Overall, the relapse rate was 62%.  The relapse rates were 58% and 76% in females and males, respectively (P=0.001).  The mean age was 35.0±11.6 years in the relapse group (n=275) and 32.6±11.3 in the remission group (n=164) (P=0.03).  T4 was 20.4±6.3 and 18.1±5.4 mg/dl in the relapse and remission groups, respectively (P=0.000).  In the relapse group, T3 was 443.0±189.5 ng/dl and in the remission group, it was 373.4±182 ng/dl (P=0.009).  T3 to T4 ratio was higher in the relapse group (21.8±8.3 vs 18.6±7.0 ng/mg, P<0.005).  Larger pre-and post-treatment thyroid size were associated with higher relapse rate (P<0.05 and P=0.001, respectively).  Logistic regression analysis showed that male sex, old age, higher pretreatment T4, T3, and T3 to T4 ratio, and larger pre-and post-treatment thyroid size were associated with higher relapse rates.  Iodinated salt consumption and duration of treatment beyond 12 months had no effect on the relapse rate. Conclusion: Patients with male gender, older age, higher pretreatment T3, T4 higher T3/T4 ratio, and larger thyroid size before and after treatment have higher risk of relapse.