Assessment of the Toronto Psoriatic Arthritis Screen 2 as a Screening Tool for Psoriasis

Background Psoriasis is a chronic inflammatory disease affecting multiple organ systems and resulting in reduced quality of life for many patients. A screening tool would be useful, particularly in underserviced or research settings with limited access to dermatologists. The Toronto Psoriatic Arthritis Screen, version 2 (ToPAS 2) is a validated screening tool for psoriatic arthritis containing questions specific for psoriasis. Objectives To evaluate the performance of skin-specific questions from ToPAS 2 for the diagnosis of psoriasis. Methods Participants aged >18 were recruited from Dermatology and Family Medicine clinics and completed the ToPAS 2 questionnaire prior to being examined by a dermatologist for psoriasis. Two scoring indexes were derived from the ToPAS 2 skin-related questions using backward selection regression models. Statistical analysis was performed using receiver operating characteristic (ROC) curves to measure their performances. Results Two hundred and fifty eight participants were recruited. 32 (12%) were diagnosed with psoriasis by dermatologist assessment. Index 1 includes all 5 skin-related questions from ToPAS 2, while Index 2 includes three of the five questions. Both indexes demonstrate high specificity (82% to 92%), sensitivity (69% to 84%), and excellent negative predictive value (NPV) (>95%) for a diagnosis of psoriasis. The overall discriminatory power of these models is 0.823 (Index 1) and 0.875 (Index 2). Conclusions Skin-related questions from ToPAS 2 have discriminatory value in detecting psoriasis, specifically questions relating to a family history, a prior physician diagnosis of psoriasis or a rash consistent with images of plaque psoriasis. This study is a valuable step in developing a screening tool for psoriasis.