MONTREAL — Injury, heavy lifting, severe infection, or other forms of trauma were associated with the progression of psoriasis to psoriatic arthritis in a case-control study.
“All we're talking about here is an association. We can't infer causation,” the study's principal investigator, Dr. Dafna Gladman, said in an interview.
Previous, less-rigorous studies have suggested an association between trauma and psoriatic arthritis (PsA), said Dr. Gladman, professor of medicine at the University of Toronto. “This study supports that notion—that environmental factors are important—but we think genetic factors are also involved,” as well as immunologic factors, she said.
At most, 30% of psoriasis patients go on to develop PsA, Dr. Gladman noted.
Her study, presented as a poster at the annual meeting of the Canadian Rheumatology Association, compared 159 patients who had PsA with the same number of control patients who had psoriasis alone.
Men accounted for a similar percentage of both study groups (46% in the PsA group and 44% in the control group). The mean age of the participants in each group was similar (45 years and 48 years), as was the mean duration of psoriasis (17.5 years and 18.5 years). The mean duration of PsA was 3 years. All the patients with psoriasis were examined to ensure they didn't have psoriatic arthritis.
All of the patients completed a questionnaire to assess environmental factors during the past 10 years, including occupational trauma, infection, immunization, smoking, and psychological stress.
In a univariate analysis, a history of infection requiring hospitalization was the strongest risk factor for the development of PsA, with an odds ratio of 11.7. (Infective diarrhea carried an OR of 2.11.)
The second-highest risk factor was in the category of occupational exposure. A history of work involving cumulative lifting of at least 100 lb/hr carried an OR of 2.9, and pushing cumulative loads of at least 200 lb/hr carried an OR of 1.8. The third-highest risk factor was any injury requiring medical attention (OR, 2.43).
In a multivariate logistic regression analysis, progression from psoriasis to PsA was significantly associated with severe infection requiring hospitalization (OR, 10.6), occupations requiring the lifting of heavy loads (OR, 2.7), and injuries requiring medical attention (excluding fractures and motor vehicle accidents) (OR, 2.3).
“For exposure to immunizations we found no risk, but another group [of investigators] has found that immunization was higher in those who got arthritis,” she said.
“And psychological stress had no impact, although it has been reported that psoriatic patients without arthritis have a lot of stress. In fact, they may even have more because it turns out that patients with psoriasis and no arthritis actually have worse psoriasis,” Dr. Gladman commented.
In the multivariate analysis, smoking appeared to have a significant association with decreased risk, she added. Current smoking had an OR of 0.4 and past smoking had an OR of 0.5.
The findings are too preliminary to guide clinical practice at this time, Dr. Gladman said.
Still, psoriasis patients should know that “if you have a job that requires a lot of lifting, you are more susceptible to getting psoriatic arthritis. Whether it's the only factor, we don't know, because there are also genetic factors involved. It's quite possible that in those people who are genetically predisposed, if they also do this work, they are more likely to get arthritis.”
The next step should be to look at the possible role of genetic and environmental factors, she added.
Disclosures: Dr. Gladman declared no conflicts of interest.