The Proposed PASI-HD Provides More Precise Assessment of Plaque Psoriasis Severity in Anatomical Regions with a Low Area Score.

The Psoriasis Area and Severity Index (PASI) is the most widely used clinical measure in clinical trials to assess disease severity of plaque psoriasis. However, the PASI is not a precise measure of severity with less precision when the regional area of involvement is < 10% of the BSA of a specific anatomical region. Degradation of precision results from the area score defaulting to '1' when the area of involvement within an anatomical region falls between 0% and 10% of the BSA for a given anatomical region. We describe a modification to the PASI, termed PASI-high discrimination (PASI-HD), for determination of more accurate psoriasis severity in body regions where < 10% of the body surface area is affected. The methodology for assessing disease severity in these conditions is described.