Psoriatic Arthritis Incidence Higher Than Thought

Jennifer Garcia

December 16, 2015

The incidence of psoriatic arthritis (PsA) among patients with psoriasis is higher than previously thought, according to a prospective, cohort study published online November 10 in Arthritis & Rheumatology.

Investigators led by Lihi Eder, MD, PhD, from the Centre for Prognosis Studies in the Rheumatic Diseases, Toronto Western Hospital, Ontario, Canada, followed 464 participants in the Toronto Psoriasis Cohort for a period of 8 years (January 1, 2006 - September 5, 2014). Enrollees were predominately Caucasian (77.3%) and men (56.2%) and had a mean age of 47.2 years at baseline. All had a dermatologist-confirmed diagnosis of psoriasis but were free of clinical inflammatory arthritis at baseline.

The researchers evaluated study participants at enrollment and yearly thereafter. They conducted a general physical examination, assessment of psoriasis severity (Psoriasis Area and Severity Index), and assessment of patients for the development of musculoskeletal symptoms at each visit. A diagnosis of PsA was determined by a rheumatologist on the basis of clinical, laboratory, and imaging data and whether they fulfilled the Classification of Psoriatic Arthritis (CASPAR) criteria (confirmed cases). The investigators asked patients who did not return for yearly evaluations to complete the Toronto Psoriatic Arthritis Screen, and considered those scoring 8 or higher as suspect PsA cases.

The annual incidence of confirmed PsA was 2.7 per 100 patients with psoriasis (95% confidence interval [CI], 2.1 - 3.6). Overall, 51 patients developed PsA over the course of the study, and an additional nine were considered suspect cases.

The investigators identified several independent predictors for the development of PsA in univariate analyses, including severe psoriasis (relative risk [RR], 5.39; P = .006), low level of education (university/college vs high school incomplete, RR, .22 [P = .005]; high school education vs high school incomplete, RR, .30 [P = .049]), and use of systemic retinoid medications (RR, 3.42; P = .02). In addition, psoriatic nail pitting (RR, 2.5; P = .002) and uveitis (RR, 31.5; P < .001) were time-dependent predictors for PsA development.

Some of the predictive factors have been seen in other studies, but low level of education and uveitis were not previously identified. The authors note that these findings will need to be validated in a larger patient population.

Attentive Follow-up Is Key to an Early Diagnosis of PsA

The researchers posit various reasons why the incidence of PsA was higher in this study than in those previously reported in the literature. These include differences in patient recruitment, as well as self-reported PsA diagnoses. All confirmed PsA cases in the current study were evaluated by a rheumatologist, and "[i]t is likely that we are picking up cases because of this careful follow-up," coauthor Dafna D. Gladman, MD, also from the Centre for Prognosis Studies in the Rheumatic Diseases, told Medscape Medical News.

Dr Gladman also noted that the prospective nature of the study allowed for "a more accurate estimate of the incidence of PsA among these patients, as we are actually following them at yearly intervals."

Risk of Developing PsA Continues Throughout the Course of the Disease

Of particular importance, Dr Gladman noted, was the finding that the risk of developing PsA continues throughout the course of the disease.

"We usually think that if a patient with psoriasis did not have arthritis by 10 years of disease, they are 'safe,' " said Dr Gladman. "Our data show that this is not true — that even much later in the course, patients are still at risk for developing PsA," she noted.

When asked by Medscape Medical News to comment on these study findings, Petros Efthimiou, MD, FACR, associate chief of rheumatology at New York Methodist Hospital, New York City, said "While this study identified some important epidemiological factors that may lead to the development of PsA after the patient has been diagnosed with psoriasis, we are still unable to predict which patient will develop [PsA]."

He concluded, "Additionally, the findings may not reflect the incidence of PsA in psoriasis patients that may have mild or moderate disease that are being followed by community physicians and may be quite different from the patients that constituted the cohort studied, where patients with more severe disease were abundant."

The authors and Dr Efthimiou have disclosed no relevant financial relationships.

Arthritis Rheumatol. Published online November 10, 2015. Abstract

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