Blue-collar work may amplify inflammatory impact of smoking in axial SpA
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Baseline smoking is strongly associated with worse MRI sacroiliac joint inflammation among blue-collar or “low education” patients with axial spondyloarthritis, according to data published in Arthritis & Rheumatology.
“Smoking and systemic inflammation have been shown to independently associate with spinal radiographic progression in axial SpA,” Elena Nikiphorou, MBBS/BSc, FRCP, MD(Res), PGCME, FHEA, of Leiden University Medical Center, in the Netherlands, told Healio Rheumatology. “In previous studies, it has been shown that the association particularly between systemic inflammation and spinal radiographic progression can be amplified in patients who smoke compared to patients who do not smoke and in those with physically demanding jobs — also known as blue-collar jobs — compared to patients with more sedentary or office-based jobs — also known as white-collar type jobs.”
To assess the association between smoking and imaging outcomes over 5 years among patients with axial SpA, and to analyze the potential impact of socioeconomic factors, including job type, on this association, Nikiphorou and colleagues recruited participants from 25 centers across France as part of the prospective, longitudinal DESIR cohort. In all, the researchers included 406 patients with axial SpA who met the Assessment of Spondyloarthritis international Society (ASAS) criteria, had at least one imaging outcome available, and baseline information on smoking and socioeconomic factors.
The researchers assessed four imaging outcomes — including spine and sacroiliac joint radiographs — along with spine MRI, by three central readers at baseline as well as 2 and 5 years. Baseline smoking status was identified as the explanatory variable of interest. Potential links between smoking and socioeconomic status, specifically job type and education, were tested and, if significant, the researchers proceeded to analyses in separate strata. In addition, they used generalized estimating equations models, adjusted for confounders.
According to the researchers, 40% of the included participants were smokers, and 18% were identified as blue collar. Smoking was independently associated with more sacroiliac joint inflammation on MRI at each visit over 5 years. Moreover, this effect was seen only in bluecollar patients ( = 5.41; 95% CI, 1.35-9.48) and, in a separate model, in those with low education ( = 2.65; 95% CI, 0.42-4.88).
“We found smoking to be significantly associated with more MRI-SIJ inflammation over 5 years only in patients with blue-collar jobs,” Niphorou said. “A similar effect was found in patients with low education.”
Smoking was also significantly associated with spinal inflammation ( = 1.69; 95% CI, 0.45-2.93) and sacroiliac joint damage ( = 0.57; 95% CI, 0.18-0.96) across all patients regardless of socioeconomic factors or other potential confounders.
“The strong association between smoking and MRI-sacroiliac-joint inflammation over time in patients with axial SpA with blue-collar job type, or with low education, was irrespective of other socioeconomic factors, systemic inflammation or treatment,” Nikiphorou said. “The findings support a possible role for mechanical stress, for example as seen with physically demanding jobs, amplifying the effect of smoking on sacroiliac joint inflammation in axial SpA, in line with previous findings of translational research.”
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