Influence of smoking and obesity on treatment response in patients with axial spondyloarthritis: a systematic literature review

To assess whether smoking and obesity are predictors of poor treatment response in patients with axial spondyloarthritis (axSpA). A systematic literature review was performed by searching in MEDLINE and EMBASE up to June 2019 with a strategy based on the PICO approach: Population: patients with axSpA; Intervention or exposure: smoking or obesity; Comparison: non-smokers (for smoking) and normal-weight individuals (for obesity); and Outcome: any response criteria currently validated for axSpA. The 2009 Oxford Centre for Evidence-based Medicine levels were used for assessing the studies quality. Out of 1873 references retrieved, 46 studies were selected for full-text review and 12 for data extraction: six stratified patients by smoking and six by obesity. All were longitudinal observational studies, except one, which was cross-sectional. Overall, these studies included 5291 patients (3917 for smoking and 1333 for obesity), and all these patients were on anti-tumor necrosis factor (anti-TNF) therapy. The quality of evidence was graded as level 2b except that from the cross-sectional study which was graded level 4. For smoking, the evidence found is inconsistent: two studies finding negative effects in response to anti-TNF while the other four found no differences in clinical response to this therapy. Regarding obesity, the evidence is more consistent: five of the six studies describing a negative influence in response to anti-TNF. According to the scientific evidence in patients with axSpA, obesity is associated with a more unsatisfactory response to anti-TNF therapy. A poorer response in smokers has yet to be demonstrated. Key Points • Identifying predictors of treatment response in axSpA, especially those that are modifiable, is relevant. • Obesity increases the risk of poorer response to anti-TNF agents in patients with axSpA. • Scientific evidence for smoking habit as a predictor of treatment response in axSpA is inconclusive.

Keywords: Ankylosing spondylitis; Axial spondyloarthritis; Body mass index; Clinical response; Efficacy; Obesity; Outcome; Overweight; Predictors; Tobacco.