Prevalence of rheumatologist-diagnosed psoriatic arthritis in patients with psoriasis in European/North American dermatology clinics.

Background: Prompt identification and treatment of psoriatic arthritis (PsA) in patients with psoriasis is critical to reducing the risk of joint damage, disability, and comorbidities.

Objective: We sought to estimate PsA prevalence in patients with plaque psoriasis in 34 dermatology centers in 7 European and North American countries.

Methods: Consecutive patients were evaluated by dermatologists for plaque psoriasis and subsequently by rheumatologists for PsA. PsA prevalence was estimated primarily based on rheumatologists' assessment of medical history, physical examination, and laboratory tests.

Results: Of 949 patients evaluated, 285 (30%) had PsA (95% confidence interval 27-33) based on rheumatologists' assessment. PsA diagnosis changed in 1.2% of patients when diagnostic laboratory tests were added to medical history and physical examination. Of 285 patients given the diagnosis of PsA, 117 (41%) had not been previously given the diagnosis.

Limitations: Bias may have been introduced by lack of standardized diagnostic criteria and unbalanced recruitment based on country populations.

Conclusions: In this study, almost a third of patients with psoriasis seen in dermatology centers had PsA as determined by rheumatologists. More than a third of patients with PsA had not been previously given the diagnosis. Clinical evaluation alone is often sufficient basis for PsA diagnosis, but laboratory test results may be helpful in some patients.