Simplified Psoriasis Severity Measure Shows Strong Correlation With PASI

A simplified measure for assessing plaque psoriasis severity demonstrated excellent reliability and a strong correlation with the standard Psoriasis Area and Severity Index (PASI) in a large Canadian cohort, according to research published in JEADV Clinical Practice.¹

The Gulliver-Gestalt-Psoriasis Area Severity Estimate (G2-PASE) was developed to address a longstanding challenge in dermatology practice: while PASI remains the reference standard for measuring psoriasis severity in clinical trials, its complexity and time requirements make it impractical for routine clinical use,² the authors explained.

The researchers analyzed data from 1803 Canadian patients with moderate to severe plaque psoriasis enrolled in the Psoriasis Longitudinal Assessment and Registry (PSOLAR). The study calculated G2-PASE scores using baseline Physician Global Assessment (PGA) and body surface area (BSA), which are values already collected in the registry, and then compared these with recorded PASI scores.

“More straightforward measures such as the simplified PASI, PGA×BSA, and lattice system PGA were developed to improve practicality, but limited validation in diverse settings, weak correlation at the extremes of disease severity, and failure to align closely with the nonlinear weighting of the PASI hindered their clinical adoption,” the authors wrote.¹ “A recent registry analysis suggested that combining BSA and global assessment may best approximate PASI but requires validation.”

The results showed a Pearson correlation coefficient of 0.83, indicating a very strong correlation between the measures. The standardized Cronbach coefficient alpha was 0.91, demonstrating excellent reliability. The mean baseline PASI score was 5.52, and the mean calculated G2-PASE score was 8.37.

Unlike earlier simplified tools, G2-PASE incorporates a nonlinear BSA modifier that better aligns with PASI's nonlinear weighting system. The calculation uses PGA scores multiplied by an arbitrary constant of 3—representing the 3 qualitative lesion characteristics in PASI (erythema, induration, and scale)—along with a Gestalt BSA value raised to a variable exponent based on disease extent.

“Previous work comparing PASI and PGA measures in randomized trials showed strong overall correlation, yet linear proxies such as PGA×BSA tend to underestimate disease severity at lower PASI values,” the authors wrote. “By incorporating a nonlinear modifier for BSA, G2-PASE aligns more closely with PASI weighting and appears suitable for patients with moderate to severe disease typical of PSOLAR participants.”

The correlation between G2-PASE and PASI remained consistent across the full range of observed PASI scores from 0 to 64, indicating the tool performs well across mild, moderate, and severe disease presentations.

One notable advantage of G2-PASE is its potential for retrospective application, the authors noted. Because it relies on PGA and BSA measurements that dermatologists routinely record, the tool can calculate disease severity estimates from existing chart or registry data even when PASI scores were never obtained.

The study had several limitations. Researchers analyzed only baseline cross-sectional data rather than longitudinal outcomes, so G2-PASE's performance in tracking treatment response over time remains unexamined. The findings may apply specifically to populations similar to PSOLAR participants, alhough the Canadian cohort included 37 sites across diverse geographic and demographic regions. The study also assumed high interrater reliability for the measures used.

The authors acknowledged that G2-PASE, like standard PASI, focuses on disease characteristics rather than incorporating patient-reported outcomes or high-impact site involvement, which also influence disease severity.

“Although PASI remains the gold standard for grading psoriasis severity, its utility is not universally practical,” the authors wrote. “In busy community practices or subspecialty settings where psoriasis is not the primary focus, PASI scoring may not be routinely performed, limiting its usefulness for monitoring and documentation of disease status. The G2-PASE offers a pragmatic alternative by using PGA and BSA, 2 measures familiar to dermatologists, and applying a nonlinear correction that mirrors PASI weighting.”

The researchers emphasized that these findings should be viewed as preliminary, requiring confirmation in independent, longitudinal, and international cohorts before broader clinical implementation.

Reference

1. Gulliver WP, Langholff W, Guenther L, et al. G2-PASE: a novel, rapid, and reliable measure of plaque psoriasis severity. JEADV Clin Pract. Published online January 12, 2026. doi:10.1002/jvc2.70293

2. Spuls PI, Lecluse LL, Poulsen ML, Bos JD, Stern RS, Nijsten T. How good are clinical severity and outcome measures for psoriasis?: quantitative evaluation in a systematic review. J Invest Dermatol. 2010;130(4):933-943. doi:10.1038/jid.2009.391