Product of the Physician Global Assessment and body surface area: A simple static measure of psoriasis severity in a longitudinal cohort

Background: The Psoriasis Area and Severity Index (PASI) is considered the gold standard assessment tool for psoriasis severity, but PASI is limited by its complexity and insensitivity in people with mild psoriasis. Objective: We sought to evaluate the product of a Physician Global Assessment (PGA) and Body Surface Area (BSA) (PGAxBSA) as an alternative to PASI. Methods: Psoriasis severity was evaluated at 6-month intervals in participants of the Utah Psoriasis Initiative registry. Correlation coefficients were used to compare PGAxBSA with PASI and the Simplified PASI (SPASI). Results: Between August 2008 and November 2010, 435 assessments were completed in 226 participants. The median PASI score was 3.2 (interquartile range 1.8-5.4) and the median BSA was 3.0% (interquartile range 1.0%-5.0%). PGAxBSA had higher correlations with PASI than SPASI (0.87 vs 0.76, P < .001). PGAxBSA also had higher correlations with a Global Patient Assessment of psoriasis severity (0.65) than both PASI (0.59, P <. 001) and SPASI (0.51, P <. 001). Limitations: The use of PGAxBSA for measuring severe psoriasis and response to therapy is unclear, because most participants had mild to moderate psoriasis and data were not collected at predefined intervals in relation to therapy initiation. Interrater reliability was not assessed. Conclusions: PGAxBSA is a simple and sensitive instrument for measuring psoriasis severity.