Background In axSpA, the effect of disease activity on radiographic progression over time is more pronounced in males and smokers, but the reason for this is unclear. Recently, we have demonstrated a longitudinal relationship between MRI-inflammatory lesions and clinical disease activity measures (DA) in males, but not in females. However, whether or not there is also a disparity in this relationship based on the smoking status is unknown.

Objectives To investigate the role of smoking status in the longitudinal relationship between inflammatory lesions on MRI of the spine and DA in patients with axSpA.

Methods Two-year follow-up data from 164 patients fulfilling ASAS axSpA criteria in the DESIR cohort with ≥2 MRIs of the spine available during this period were analysed. Interactions were tested between smoking status and DA (ASDAS, BASDAI, patient's global disease activity, night pain, CRP and ESR) on the longitudinal relationship with MRI of the spine (Berlin score), analysed with a GEE model of i) absolute and ii) change scores. All models were adjusted for age, symptom duration and HLA-B27. Since there was a significant interaction with gender in previous analyses, analyses were repeated in males and females separately.

Results Baseline characteristics of patients included were: 50% males, mean (SD) age: 33 (9) years, 39% smokers, 82% HLA-27+ and symptom duration: 18 (11) months. A significant interaction with smoking status was found for most of the DA, indicating that the relationship between MRI-inflammatory lesions and DA was different in smokers than in non-smokers. In the model of absolute scores (i), MRI-scores were statistically significantly related to most of the DA in smokers, while only CRP was significantly and weakly related in non-smokers (Table 1A). In the model of changes (ii), ASDAS and pain at night remained significantly related to MRI-inflammatory lesions, but no statistically significant relationship between MRI and DA was found in non-smokers (Table 1B). When stratifying for gender, the subgroups were small and the relationships were no longer statistically significant.

Conclusions In patients with axSpA, there is a longitudinal relationship between MRI inflammatory lesions of the spine and DA in smokers, but not in non-smokers. This disparity may explain the stronger effect of disease activity on radiographic progression observed in smokers.

Whether both gender and smoking have an effect on this relationship between MRI and DA remains to be elucidated.

Acknowledgement Pfizer

Disclosure of Interest None declared