Objective: To evaluate an existing tool (the Swedish modification of the Psoriasis Assessment Questionnaire) and to develop a new instrument to screen for psoriatic arthritis in people with psoriasis.
Design: The starting point was a community-based survey of people with psoriasis using questionnaires developed from the literature. Selected respondents were examined and additional known cases of psoriatic arthritis were included in the analysis. The new instrument was developed using univariate statistics and a logistic regression model, comparing people with and without psoriatic arthritis. The instruments were compared using receiver operating curve (ROC) curve analysis.
Results: 168 questionnaires were returned (response rate 27%) and 93 people attended for examination (55% of questionnaire respondents). Of these 93, twelve were newly diagnosed with psoriatic arthritis during this study. These 12 were supplemented by 21 people with known psoriatic arthritis. Just 5 questions were found to be significant predictors of psoriatic arthritis in this population. Figures for sensitivity and specificity were 0.92 and 0.78 respectively, an improvement on the Alenius tool (sensitivity and specificity, 0.63 and 0.72 respectively).
Conclusions: A new screening tool for identifying people with psoriatic arthritis has been developed. Five simple questions demonstrated good sensitivity and specificity in this population but further validation is required.