Importance: Psoriasis and obesity are strongly linked, and weight loss appears to improve psoriasis symptoms and severity. Bariatric surgery may induce remission of psoriasis, but data are limited to small studies and case series.
Objective: To examine the incidence and prognosis of psoriasis and psoriatic arthritis in patients undergoing bariatric surgery (gastric bypass and gastric banding).
Design, setting, and participants: This population-based cohort study used individual-level linkage of administrative and public health registers in Denmark. All Danish citizens who received gastric bypass or gastric banding between January 1, 1997, and December 31, 2012, were included in the study. Data analysis was performed from February 4 to April 14, 2016.
Main outcomes and measures: The outcomes were incident (new-onset) psoriasis or psoriatic arthritis, or progression to severe psoriasis. Incidence rates per 1000 person-years were calculated, and crude and adjusted hazard ratios (HRs) were estimated by Cox regression models and presented with 95% CIs. The HRs were obtained by comparing the risk in the cohort of patients presurgery and postsurgery, with the presurgery groups serving as the reference groups.
Results: We identified 12 364 and 1071 patients receiving gastric bypass and gastric banding, respectively. The gastric bypass subset was composed of 9480 (76.7%) women and 2884 (23.3%) men at the study start; the mean (SD) age of these patients was 27.8 (10.1) years at the study start and 41.0 (10.0) years at the time of surgery. The gastric banding subset was composed of 800 (74.7%) women and 271 (25.3) men; the mean (SD) age of these patients was 32.3 (10.1) years at the study start and 41.7 (10.0) years at the time of surgery. Adjusted HRs of psoriasis were 0.52 (95% CI, 0.33-0.81) and 1.23 (95% CI, 0.40-3.75) for gastric bypass and gastric banding, respectively. Similarly, adjusted HRs of progression to severe psoriasis were 0.44 (95% CI, 0.23-0.86) and 1.18 (95% CI, 0.12-11.49) for gastric bypass and gastric banding, respectively. Adjusted HRs of psoriatic arthritis were 0.29 (95% CI, 0.12-0.71) and 0.53 (95% CI, 0.08-3.56) for gastric bypass and gastric banding, respectively.
Conclusions and relevance: Gastric bypass was associated with a significantly reduced risk and improved prognosis of psoriasis and psoriatic arthritis, whereas gastric banding was not. This finding may be caused by the postoperative differences in nutrient intake and/or weight loss as well as differences in the secretion of hormones that potentially modulate inflammation.