Ten Year Outcome of Anti-Thyroid Drug Treatment for First Episode Graves' Thyrotoxicosis: The Predictive Importance of TRAb.

Objective: To establish the risk and time course of recurrent thyrotoxicosis following withdrawal of anti-thyroid drugs (ATD) and risk factors for recurrence.

Design: Single-centre retrospective study.

Methods: Two hundred and ninety people with a first episode of Graves' thyrotoxicosis, who completed a course of ATD, were included. Clinical and biochemical parameters associated with recurrence risk were assessed over a 10-year period.

Results: Recurrence occurred in 54% of individuals over a 10-year period, with 73% occurring within 2 years. Younger age (41 years [33-51] vs. 47 [39-56], p = 0.011), higher TSH receptor antibody (TRAb) at diagnosis (8.8 IU/L [4.9-17.2] versus 6.0 [4.1-9.9], p = 0.002), higher TRAb at cessation of ATD (1.3 [<0.9-2.3] vs. 1.0 [<0.9-1.3], p < 0.001), longer time to normalisation of TSH (6 months [3-9] vs. 4 [2-7], p 0.013) and longer time to normalisation of fT4 (2 months [1-3] vs. 1 [1-2], p = 0.001) were all associated with relapse within 10 years. Recurrence within 10 years occurred in 74% of individuals with TRAb > 12 IU/L at diagnosis but only 44% of those with TRAb < 5 IU/L at diagnosis (p = 0.001). TRAb (at diagnosis and cessation) and age were independently associated with relapse in multivariate analysis.

Conclusions: Most recurrent thyrotoxicosis occurs within the first few years after ATD withdrawal. TRAb concentration, at diagnosis and cessation of ATD, is a useful predictor of recurrence risk and can be used to inform decisions on the optimal approach to primary therapy.