Psoriatic arthritis may occur more frequently among people with psoriasis than previously reported, and risk factors include having severe psoriasis, nail pitting, low education levels, and uveitis, according to findings from a Canadian cohort study.
Beginning in 2006, Dr. Lihi Eder of the University of Toronto and coinvestigators recruited 464 patients (mean age 47, 56% male, 77% white) mainly from phototherapy and dermatology outpatient clinics in Toronto, and followed them 8 years. All had psoriasis of varying type and severity at baseline, but not inflammatory arthritis or spondylitis (Arthritis Rheumatol. 2015 Nov 10 doi: 10.1002/art.39494).
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During the 8-year follow-up, 51 patients developed rheumatologist-confirmed psoriatic arthritis (PsA). Dr. Eder and colleagues reported an annual incidence rate of 2.7 confirmed cases of psoriatic arthritis per 100 psoriasis patients per year, which is considerably higher than previous published estimates, the investigators noted. The independent predictors of confirmed psoriatic arthritis were severe psoriasis (relative risk, 5.4; P = .006), not finishing high school (vs. finishing college RR, 4.5, P = .005; and vs. finishing high school RR, 3.3; P = .049), and use of systemic retinoids (RR, 3.4; P = .02). Time-dependent predictive variables included psoriatic nail pitting (RR, 2.5; P = .002) and uveitis (RR, 31.5; P = .001). Disease severity and nail pitting have been found in previous studies to be associated with a higher risk of psoriatic arthritis.
This study confirmed this association and also identified low education levels and uveitis as predictors. Low education is a marker of socioeconomic status that has been associated with lifestyle habits and possibly occupations that may increase PsA risk, the study authors noted, but the link requires further investigation. The authors cautioned that only three uveitis cases occurred in the cohort and that confidence intervals were wide. They also noted as a limitation that most participants were recruited from dermatology clinics, leading to overrepresentation of moderate-severe psoriasis and possibly patients with longer disease duration. Nevertheless, it “is likely that the true incidence of PsA in patients with psoriasis, particularly those attending dermatology clinics, is higher than previously reported,” the investigators wrote. “This highlights the role of dermatologists as key players in identifying psoriasis patients who are at higher risk of developing PsA.”
Krembil Foundation, the Canadian Institutes of Health Research, and The Arthritis Society supported the study.