Limitations in screening instruments for psoriatic arthritis: a comparison of instruments in patients with psoriasis

To compare the abilities of 3 validated screening instruments to predict the diagnosis of psoriatic arthritis (PsA) in patients with psoriasis.

Prior to a rheumatologic evaluation, 213 participants in the Utah Psoriasis Initiative completed the Psoriasis Epidemiology Screening project (PEST), the Toronto Psoriatic Arthritis Screen (ToPAS), and the Psoriatic Arthritis Screening and Evaluation (PASE). Previously established instrument cutoff scores were used to designate positive and negative classifications. Sensitivities and specificities were determined by comparing instrument classifications to the rheumatologist's diagnosis. Phenotypic features and alternative diagnoses were compared between participants who screened positively and negatively on each instrument. Discrepancies between the rheumatologist's examination findings and responses to specific instrument questions were compared.

The sensitivities of PEST, ToPAS, and PASE were 85%, 75%, and 68%, and the specificities were 45%, 55%, and 50%, respectively. The instruments were less sensitive in patients with lower disease activity, fewer PsA features, and shorter disease duration. The instruments did not consistently differentiate between PsA and other types of musculoskeletal disease. Discrepancies between examination findings and responses to instrument questions occurred more frequently with ToPAS than with PEST and PASE.

Sensitivities and specificities for PEST, ToPAS, and PASE were lower than previously reported. This population included patients with PsA and other types of musculoskeletal disease and may represent those most likely to complete a screening instrument and follow through with a rheumatology referral. Further analyses may enable the development of more successful screening strategies for PsA in psoriasis patients with musculoskeletal complaints.