From JAMA Surgery

Gastric bypass surgery was associated with more than a 50% drop in baseline rates of psoriasis, and with about a 70% decrease in the incidence of psoriatic arthritis, investigators reported.

In contrast, gastric banding did not appear to affect baselines rates of either of these autoimmune conditions, Alexander Egeberg, MD, of Herlev and Gentofte Hospital, Hellerup, Denmark, and associates reported in JAMA Surgery. “Although speculative, these findings may be the result of post-operative differences in weight loss and nutrient uptake, as well as differences in the postsurgical secretion of a number of gut hormones, including [glucagon-like peptide-1],” they wrote.

Psoriasis strongly correlates with obesity, and weight loss appears to mitigate psoriatic symptoms, the investigators noted. Previously, small studies and case series indicated that bariatric surgery might induce remission of psoriasis. To further investigate this possibility, Dr. Egeberg and his associates conducted a longitudinal cohort study of all 12,364 patients who underwent gastric bypass surgery and all 1,071 patients who underwent gastric banding in Denmark between 1997 and 2012 (JAMA Surg. 2017;152:344-349). No patient had psoriasis symptoms at the start of the study. A total of 272 (2%) gastric bypass patients developed psoriasis before their surgery, while only 0.5% did so afterward. In contrast, gastric banding was not tied to a significant change in the incidence of psoriasis – the preoperative rate was 0.5%, and the postoperative rate was 0.4%. Similarly, respective rates of psoriatic arthritis were 0.5% and 0.1% before and after gastric bypass, but were 0.3% and 0.6% before and after gastric banding. Additionally, respective rates of severe psoriasis were 0.8% and 0% before and after gastric bypass, but were about 0.2% and 0.5% before and after gastric banding.

After adjusting for age, sex, alcohol abuse, socioeconomic status, smoking, and diabetes status, gastric bypass was associated with about a 48% drop in the incidence of any type of psoriasis (P = .004), with about a 56% drop in the rate of severe psoriasis (P = .02), and with about a 71% drop in the rate of psoriatic arthritis (P = .01). In contrast, neither crude nor adjusted models linked gastric banding to a decrease in the incidence of psoriasis, severe psoriasis, or psoriatic arthritis, the researchers said.

Gastric banding is “a purely restrictive procedure,” while gastric bypass – especially Roux-en-Y bypass – diverts nutrients to the distal small intestine, where enteroendocrine cells secrete GLP-1, the researchers wrote.

“These postoperative hormonal changes may, in addition to the weight loss, be important for the antipsoriatic effect of gastric bypass,” they added. “Both gastric bypass and gastric banding have been shown to lead to sustained weight loss, suggesting that the observed differences in our study might be caused by factors other than weight loss.”

An unrestricted research grant from the Novo Nordisk Foundation funded the work. Dr. Egeberg disclosed ties to Pfizer and Eli Lilly. One coinvestigator disclosed ties to these and several other pharmaceutical companies.