Background We have shown that disease activity has an effect on radiographic progression over the long-term and that gender and symptom duration are effect modifiers. Smoking has been shown to predict radiographic progression.
Objectives To investigate whether smoking influenced this longitudinal relationship between disease activity and radiographic damage.
Methods Patients from the Outcome in AS International Study (OASIS) were followed-up for 12 years, with biannual clinical and radiographic assessments. Two readers independently scored the x-rays according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) and scores were averaged. Disease activity was assessed by the ASDAS-CRP. The relationship between ASDAS and radiographic damage was investigated using generalized estimating equations, with auto-regressive (i.e. adjusted for the 2-year previous mSASSS) models with a 2-year time-lag. Interactions were tested with baseline smoking status and if significant, analyses were repeated in strata.
Results A total of 127 patients were included (71% males, mean (SD) age 41 (12) years, mean symptom duration 18 (11) years and 82% HLA-B27 positive). Smoking status modified the relationship between disease activity and radiographic damage significantly (p<0.001), and this effect extended to other strata: males (p=0.002) and patients with shorter symptom duration (<18y) (p=0.009); Overall, an increase in one ASDAS-unit led to an increase in 0.72 mSASSS-units per 2 years. In smokers, this value reached 1.94 mSASSS-units and in male smokers 2.15 mSASSS-units (Table). Comparing the magnitude of the effect of ASDAS on mSASSS in smokers vs non-smokers, smokers had a 5.5 fold amplified effect, whereas male smokers had a 13.4 fold amplified effect compared to female non-smokers. Smokers with short symptom duration had a 8.1-fold amplified effect compared to non-smokers with long symptom duration (Figure).
Conclusions Smoking amplifies the effect of disease activity on radiographic damage (5-fold). This effect is further amplified in male smokers (13.4-fold) in comparison with female non-smokers.
Disclosure of Interest : None declared