RALEIGH, N.C. – Psoriasis patients are at a nearly fourfold increased risk of developing Crohn’s disease, and the risk is higher in psoriatic arthritis patients.
These findings from 174,646 prospectively followed participants in the Nurses’ Health Study and the Nurses’ Health Study II are consistent with the results of genomewide association studies which have found susceptibility genes common to both psoriasis and inflammatory bowel disease, especially genes in the interleukin-23 pathway, Dr. Wenqing Li said at the annual meeting of the Society for Investigative Dermatology.
"Further understanding of the mechanisms that mediate both psoriasis and Crohn’s disease could eventually lead to elucidation of new targets for interventions that may modulate the incidence or activity of both diseases," added Dr. Li of Harvard Medical School, Boston.
Of note, the psoriasis patients were not at significantly increased risk for developing ulcerative colitis. This suggests that psoriasis may share fewer overlapping pathways with ulcerative colitis than it does with Crohn’s disease, he continued.
Women in the Nurses’ Health Study were prospectively followed from 1996 to 2008, whereas those in the NHS II were followed from 1991 to 2005. During follow-up, there were 188 incident cases of Crohn’s disease and 240 of ulcerative colitis in the study population. All diagnoses of inflammatory bowel disease were confirmed by two gastroenterologists blinded as to whether or not the affected patients also had psoriasis, Dr. Li noted.
The combined analysis of the two studies included 47,618 person-years of prospective follow-up of psoriasis patients and 2,401,883 person-years of follow-up of participants without psoriasis. The psoriasis patients had an age-adjusted 3.74-fold increased risk of developing Crohn’s disease.
Having psoriasis was still an independent risk factor for Crohn’s disease, with an associated 3.5-fold relative risk, in a multivariate analysis that was adjusted for body mass index, physical activity, smoking status, alcohol consumption, use of oral contraceptives, and postmenopausal hormone therapy as well as age.
Based upon 5,661 person-years of prospective follow-up of subjects with psoriasis and comorbid psoriatic arthritis, affected patients had a 6.8-fold increased of Crohn’s disease in a multivariate analysis.
Multivariate analysis was appropriate because patients with psoriasis had a higher BMI, tended to be older, consumed more alcohol, and were less physically active than were those without psoriasis. The psoriasis patients were also more likely to be current smokers, users of oral contraceptives, and current users of postmenopausal hormone therapy.
The risk of new-onset Crohn’s disease was significantly greater among psoriasis patients whose dermatologic disease was diagnosed when they were younger than 40 years than it was among those diagnosed later in life. The risk was also greater in those with at least a 10-year history of active psoriasis. However, as 87% of patients with psoriasis had mild skin disease based upon the involved body surface area, this study didn’t have sufficient power to determine if the risk of Crohn’s disease was greater in individuals with more severe psoriasis, according to Dr. Li.
To ensure that the increased risk of inflammatory bowel disease associated with having psoriasis wasn’t in some way affected by the use of tumor necrosis factor inhibitors to treat psoriasis, Dr. Li and coinvestigators conducted a separate analysis restricting follow-up through 2004, the year the biologic therapies were approved for psoriasis. This didn’t change the results.
The studies were sponsored by the National Institutes of Health. Dr. Li reported having no financial conflicts.