Tasmania is an iodine deficient island and response to anti-thyroid medication in Graves’ disease has not been reported in the Tasmanian population. Predictors of anti-thyroid medication efficacy would be valuable for guiding clinical decisions. Our previous study of 52 patients highlighted the importance of following patients >4 years after ceasing treatment to detect long-term remission. In this study we included 143 patients and investigated long-term remission, relapse and non-resolution from medical treatment over 5 years and explored potential predictors of response to anti-thyroid medication.
We retrospectively analysed Royal Hobart Hospital endocrine clinic patients with positive TSH receptor antibodies (TRAb >1.75) diagnosed with Graves’ prior to 2012 and treated with a dose titration schedule of carbimazole or propylthiouracil.
40 patients remitted, 60 relapsed and 43 had no resolution. Average treatment duration for remission was 22.8 +/-3.8 months and relapse was 17.9 +/-1.7 months. Presenting FT4 was lower in remission (32.6 +/-3.0, p<0.001) and relapse (38.8 +/-2.8, p<0.01) compared to non-resolution (51.7 +/-3.9). Presenting TRAb was higher in non-resolution (20.4 +/-2.5) compared to relapse (11.2 +/-1.5, p<0.01) and remission (8.9 +/-1.5, p<0.001). Final TRAb was lower in remission (1.3 +/-0.2) than relapse (3.6 +/-1.0, p=0.03). Final TSH was higher in remission (1.8 +/-0.3) compared to relapse (1.3 +/-0.1, p=0.09) and non-resolution (0.6 +/-0.2, p<0.01)
In this study, 28% achieved long-term remission, 42% relapsed within 5 years and 30% had no resolution. The only significant predictor of long-term remission was decreased final TRAb. Raised TRAb and FT4 at diagnosis were also significant predictors of non-resolution from medication. We recommend at least 18m of treatment to increase potential for long-term remission and aiming for TRAb <1.0, TSH >1.0 before ceasing treatment. Early discussion with patients regarding long-term outcomes based on their individual profile should be used to guide treatment decisions.