Background We have shown that disease activity in AS leads to radiographic progression, which is accelerated in males, in those with a short disease duration, and also in smokers . A plausible biological explanation for the last relationship, however, is lacking. We hypothesize that smoking is associated with occupations that require physically demanding activities, as these were associated with more radiographic damage , and that smoking is a confounder of this relationship. Alternatively, smoking can be associated with a lower socio-economic status, which in turn could be associated with radiographic progression.
Objectives To investigate whether and how occupational physical activities and socio-economic status influence the longitudinal relationship between disease activity and radiographic damage.
Methods Patients from OASIS were followed-up for 12 years, with biannual assessments. Two readers independently scored the x-rays according to the mSASSS. Disease activity was assessed by the ASDAS-CRP. The relationship between ASDAS and radiographic progression was investigated using GEE, with a focus on subgroups, according to occupational physical activities (“white vs blue collar” jobs, i.e. manual vs “intellectual” labor), education, baseline gross monthly personal income, and baseline gross monthly family income (Table). Smoking was investigated as a covariate.
Results A total of 154 patients were included (77% males, mean (SD) age 41 (12) years, mean symptom duration 18 (11) years, 81% HLA-B27+). There was a (non-statistically significant) difference in the proportion of smokers per type of occupation (51% blue collar vs 34% white collar, p=0.077). The relationship between disease activity and radiographic progression was significantly different dependent on occupational activity (p=0.014) and on personal income (Table). In blue-collar workers, every additional unit of ASDAS resulted in a 2-year 1.19 mSASSS-units increase, compared to 0.20 mSASSS-units in white collar workers (6-fold amplification). Adjustment for smoking only partly diminished this contrast.
Conclusions Physically demanding occupational activities seem to amplify the deleterious effects of disease activity on radiographic damage in AS patients. This effect, which is partly explained by differences in socio-economic status, may be a consequence of forces acting on the spine , but may in part also be due to smoking habits. If confirmed, these findings may have implications for our commonly given advice to patients with SpA to strenuously exercise.
Ramiro 2013 ACR.
Ward 2008 A&R.
Benjamin 2009 ARD.
Disclosure of Interest None declared