Introduction: Despite high rates of recurrence after anti-thyroid drug (ATD) withdrawal, ATD (mainly Carbmazole) remain the first line of treatment for Graves disease (GD) in the UK. Limited retrospective observational studies have shown that a low TSH post ATD withdrawal had a positive predictive value of 70% and a negative predictive value of 62% (specificity 85%) for relapse of Graves disease.
Aim: We wished to determine the relationship between TSH concentration post ATD withdrawal and GD outcome, in this relatively iodine insufficient population of South Wales.
Methods and results: We recruited 100 consecutive subjects with GD, treated with ATD alone or in combination with thyroxine. 27 subjects were excluded for valid reasons (immediate recurrence after ATD withdrawal, lost to follow up, definitive therapy given as primary treatment). Of the 73 subjects analysed 59 were women; 14 men; age range 2090 years). The median duration of treatment was 13 months. 56 (76%) subjects had ATD alone but 17 (24%) had a block and replacement regime. Following withdrawal of ATD, 43 (59) remained in remission (Rem) but 30 (41%) relapsed (Rel). Thyroid function was tested at a median time of 10 weeks (range 424) following withdrawal of treatment. Median TSH concentrations in the Rem and Rel groups were 0.92 vs 0.77 mIU/l respectively (P=0.1031) (range 0.013.47 (Rem) and 0.044.38 mU/l (Rel).
Conclusions: In this group of subjects from a relatively iodine insufficient area of South Wales, serum TSH concentration at a median time 10 weeks after treatment withdrawal, did not predict outcome of GD. This was not consistent with the results of other studies from geographically disparate areas.