A pilot study on the Psoriasis Area and Severity Index (PASI) for small areas: Presentation and implications of the Low PASI score

Abstract Background: The Psoriasis Area and Severity Index (PASI) is not able to measure small affected areas in a body region which is important for assessing the performance of high-effective treatment. Objective: To present the Low PASI score, show the difference between the classic PASI and the Low PASI, evaluate the inter-observer agreement of both scores, and compare the two scores within investigators. Methods: Cross-sectional study. Two investigators independently assessed the classic PASI and the Low PASI in 10 patients with mild-to-moderate plaque psoriasis. Differences in outcome between the two scores were calculated. Intra-class correlation coefficients (ICC) were used to determine the inter-observer agreement and to compare measurements of the two scores within both investigators. Prediction limits of 95% for the errors in measurements were provided. Results: In both investigators, Low PASI was mean 1.71 and 1.76, whereas the classic PASI was mean 4.14 and 4.33. The inter-observer agreement (ICC) was excellent for both investigators in both scores (ICC classic PASI = 0.95 and Low PASI = 0.87). Conclusion: The Low PASI score allows more possible scores at lower levels of psoriasis extent (affected areas lower than 10% in a body region) compared to the classic PASI. This new score may lead to a more precise analysis of treatment responses and may have important clinical implications.