Relationship between smoking and patient-reported measures of disease outcome in ankylosing spondylitis.

OBJECTIVE: To investigate the relationship between smoking and disease activity, pain, function, and quality of life in patients with ankylosing spondylitis (AS).
METHODS: Patients with AS (n = 612) from areas across the United Kingdom took part in a cross-sectional postal survey. Patient-reported outcome measures including the Bath AS Disease Activity Index, the Bath AS Functional Index (BASFI), a numerical rating scale (NRS) of pain, the AS quality of life questionnaire (ASQoL), and the evaluation of AS quality of life measures (EASi-QoL) were analyzed in terms of smoking status and relationship with pack-year history. The influence of potential confounding factors [age, sex, disease duration, and social deprivation (Townsend Index)] were tested in multivariate logistic regression analyses.
RESULTS: Median scores of BASFI, pain NRS, ASQoL, and the 4 EASi-QoL domains were all higher in the group that had ever smoked compared to those who had never smoked (p < 0.0001, p = 0.04, p = 0.003, p < 0.02, respectively). In stepwise multivariate logistic regression analyses, high disease activity and more severe pain were associated primarily with current smoking, disease duration, and Townsend Index score, while decreased function and poor quality of life measures were associated more closely with increasing pack-year history, disease duration, and Townsend Index score. These associations were independent of age and sex.
CONCLUSION: Smoking has a dose-dependent relationship with measures of disease severity in AS. The association with increased disease activity, decreased function, and poor quality of life in smokers was independent of age, sex, deprivation level, and disease duration.