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.
Keywords: diagnosis; psoriasis; psoriatic arthritis; screening.