CheckAP: Prevalence of psoriatic arthritis (PsA) and performance evaluation of the EARP questionnaire in the population of Portuguese patients with psoriasis followed in a dermatology setting.

Background: The percentage of Portuguese psoriasis patients with psoriatic arthritis is unknown but musculoskeletal complaints related to PsA affect up to a third of patients. Dermatologists can identify early PsA as skin symptoms often precede joint symptoms in 80% of patients. Efficient and easy to perform screening tools are needed to help dermatologists effectively discriminate between Pso and PsA patients.