SAT460 Higher TSH Receptor Antibody At Diagnosis And Younger Age Predict Recurrence of Graves' Thyrotoxicosis After Thionamide Withdrawal At 10 Years

Disclosure: F.W. Gibb: None. N. Tun: None. Background: Anti-thyroid drug (ATD) therapy in Graves’ disease is generally accepted to be a safe and effective means of restoring euthyroidism. Treatment is typically administered for 12 to 18 months followed by cessation subject to certain conditions such as achieving euthyroidism on a low dose and, in some centers, exclusion of persistently elevated TSH receptor antibody (TRAb) levels. We and others have previously demonstrated the prognostic utility of TRAb at diagnosis and cessation of ATDs in predicting recurrence risk. However, very few studies have assessed recurrence risk in the long-term. Methods: Prospective observational study of thyroid status at 10 years in 231 people who completed a physician directed course of ATD for Graves’ disease (first episode). We also assessed clinical predictors of recurrence at 10 years post ATD-cessation. Results: Median age was 43 years (IQR 35 - 53) and 181/231 (78%) were female. 10 years after cessation of ATD 124/231 (53.7%) had experience a relapse of thyrotoxicosis. The following parameters were associated with recurrence at 10 years: 1. TRAb category at diagnosis: <5 IU/L (relapse 43.2%), 5 - 12 IU/L (relapse 50.0%) and >12 IU/L (relapse 71.9%) (p = 0.003). Median TRAb in those with relapse was 8.7IU/L (4.9 - 16.9) vs. 5.9 IU/L (4.1 - 9.9) in those in remission at 10 years (p = 0.002). 2. TRAb at cessation of ATD was 1.3 IU/L (<0.6 - 2.2) in relapse and 1.0IU/L (<0.6 - 1.4) in remission (p = 0.006). 3. Median age in those with relapse was 40 years (32 - 49) vs. 47 (39 - 56) in remission (p = 0.001). 4. Median fT4 at diagnosis was 33pM (26 - 42) in those with subsequent relapse vs. 30pM (24 - 36) in remission (p = 0.045) 5. Time to normalisation of fT4 was 2 months (1 - 2) in people with relapse vs. 1 month (1 - 2) in people in remission (p = 0.003). In logistic regression higher TRAb at cessation (p = 0.003) and younger age (p = 0.002) were independently associated with relapse at 10 years. Sex, smoking status and presence of ophthalmopathy did not influence recurrence risk. 73% of relapses occurred within 2 years and only 5% of relapses occurred between 5 and 10 years. At ten years, 16 patients (6.9%) had died (9 in remission and 7 after relapse), 45 were on long-term ATD (19.5%), 39 received radioiodine (16.9%), 13 had thyroidectomy (5.6%), 7 developed hypothyroidism (3.0%) and 111 were on no treatment (48.1%). Conclusions: Discussions with patients about risk of relapse should be individualised based on TRAb and age. In this cohort someone under 43 years with TRAb >12 IU/L at diagnosis had a 88% risk of relapse whilst someone older than 43 with TRAb <5 IU/L at diagnosis had a relapse rate of 38%. However, although the recurrence rate is lower in older individuals, the clinical risks of recurrent thyrotoxicosis are greater and may still support definitive therapy or long-term ATD use. Presentation: Saturday, June 17, 2023