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.