Abstract
Objective To investigate the association between cigarette smoking and hip joint involvement in ankylosing spondylitis (AS).
Methods This case-control study compared AS patients with and without hip involvement, defined by the Bath ankylosing spondylitis radiology hip index. Logistic regression analysis, subgroup analysis and sensitivity analysis were conducted to estimate the association between smoking and hip involvement in AS.
Results This study included 103 patients with hip involvement (cases) and 89 patients without (controls). In univariate analysis, patients who were juvenile-onset, younger, male, having peripheral arthritis history or cigarette exposure were prone to hip involvement. After adjusting for confounding factors, juvenile-onset (adjusted odds ratio (ORa) 2.52, 95% CI 1.26-5.06), male (ORa 2.89, 95% CI 1.14-7.33) and cigarette smoking (ORa 7.23, 95% CI 2.27-23.05) were regarded as independently associated with hip involvement in AS. Moreover, patients smoking with less than 10 pack-years exposure were 2.2 times more likely to have hip involvement than those without (ORa 2.21, 95% CI 1.09-4.47). Such association were reproduced in subgroup analysis of males and propensity score matched subjects, and it withstood sensitivity analysis.
Conclusion Smoking is a novel independent risk factor for hip involvement in AS, even less than 10 pack-years exposure could contribute to increased prevalence of hip involvement in AS, which underlined the giant significance of smoking cessation in AS patients, especially for juvenile-onset AS.
