Endocrine Abstracts

Background: Graves’ disease is an autoimmune condition leading to hyperthyroidism and characteristically elevated TSH receptor antibody (TRAb). TRAb levels typically fall post-treatment with anti-thyroid drugs (ATDs) and are used in identifying risk of relapse. Tobacco smoking is a risk factor for reduced treatment efficacy of ATDs. We intended to evaluate the effect of smoking on changes in TRAb levels in patients treated for Graves’ disease.

Methods: We analysed a database that prospectively collected information regarding patients treated for Graves’ disease at Queen Elizabeth Hospital, Gateshead. Inclusion criteria was any patients treated for 9 months or longer with ATD. TRAb level data was taken at treatment initiation and 12 months (+/- 3 months). Patients without data at these two time-points were excluded (n=60). Smoking status was recorded as current smoker (CS), ex-smoker (XS), or life-long non-smoker (NS). TRAb reduction from baseline was measured as a percentage change for each group, using multivariable linear regression analyses. Other independent variables included were age, sex, race and duration of treatment with ATDs.

Results: In 374 patients, mean baseline TRAb levels for the NS, XS and CS groups were 8.9, 8.0 and 9.5 U/l, respectively. Smoking status was an independent predictor of the percentage drop in TRAb levels at 12 months (P=0.03). Current smokers had higher 12-month TRAb levels with lesser relative reduction. The number of cigarettes smoked daily demonstrated negative independent correlation with change in 12-month TRAb (P=0.03).

Conclusions: There is a significant correlation between smoking status and TRAb at 12-months, both as a relative and absolute value, which probably explains the higher relapse risk seen in CS. The extent of tobacco consumption also appears relevant, highlighting that reducing the number of cigarettes smoked may be beneficial in lowering TRAb levels and potentially the risk of relapse after ATD cessation.