Validating hf-PGA for Hand and Foot Psoriasis Severity in Adults

Hand and foot involvement in psoriasis is often disproportionate to body surface area, yet it’s strongly associated with functional impairment and reduced quality of life. A fit-for-purpose outcome measure specific to this anatomic distribution has been challenging to develop and validate. However, new psychometric data now support the Physician’s Global Assessment of Hands and/or Feet (hf-PGA) as a reliable and clinically interpretable tool for this population.

Published in Journal of Dermatological Treatment, the analysis draws on data from a multicenter, randomized, placebo-controlled phase 2b trial enrolling adults with moderate-to-severe plaque psoriasis, including patients with active hand and/or foot disease. The investigators focused on establishing reliability, validity, and a clinically meaningful change threshold for hf-PGA, aligning their approach with contemporary FDA guidance on clinical outcome assessments.

A Focused Instrument for a High-Burden Subgroup
The hf-PGA is a single-item, clinician-reported scale ranging from 0 (clear) to 4 (severe), incorporating erythema, scaling, thickening, fissures, and pustulation across the hands and feet. Unlike palmoplantar-only instruments, hf-PGA explicitly assesses overall hand and foot involvement, including dorsal surfaces, improving face validity for routine clinical and trial use.

Among 99 trial participants with hf-PGA scores of 1 or higher at baseline, the authors examined measurement properties using data from baseline, Week 8, and Week 16, irrespective of treatment assignment. This design allowed psychometric evaluation across a spectrum of disease severity and change.

Reliability That Holds Over Time
Test-retest reliability was assessed in a clinically stable subgroup, defined by no change in Investigator’s Global Assessment (IGA) score between Weeks 8 and 16. In this cohort, hf-PGA demonstrated strong score stability, with a polychoric correlation of 0.94, weighted kappa of 0.85, and 95.3% agreement. These values fall within ranges generally interpreted as excellent reliability for clinician-reported ordinal measures, supporting consistent use across visits when disease activity remains unchanged.

Construct Validity Aligned with Clinical Expectations
Validity analyses showed that hf-PGA behaves as expected relative to established global measures. At Weeks 8 and 16, hf-PGA scores correlated moderately with PASI and body surface area involvement, and more weakly but consistently with patient-reported outcomes. Importantly, worse hf-PGA severity aligned directionally with higher global disease burden and greater quality-of-life impairment. These data suggest hf-PGA captures a clinically meaningful dimension of psoriasis severity that tracks with both clinician- and patient-reported outcomes.

Defining Meaningful Change
A central contribution of this analysis lies in defining a clinically meaningful within-patient change threshold. Using methods anchored to IGA, Patient Global Impression of Severity, and Patient Global Impression of Change, the investigators found that a 2-category improvement on hf-PGA consistently aligned with meaningful improvement across anchors. This finding has practical implications for endpoint definition for treatment response in clinical trials targeting hand and foot psoriasis.

Strengths, Constraints, and Next Steps
The study benefits from prospective trial data, alignment with regulatory guidance, and inclusion of patients spanning almost clear to severe hand and foot disease. Limitations include a modest sample size, lack of inter-rater reliability assessment, and reliance on global rather than hand- and foot–specific anchors. The absence of a patient-reported hand and foot–specific symptom measure also limits insight into concordance with patient experience.

Even so, the data establish hf-PGA as a reliable and valid clinician-reported outcome with a defined meaningful change threshold. As therapeutic development increasingly targets high-impact psoriasis subtypes, hf-PGA offers a practical tool for evaluating efficacy where small surface area involvement carries outsized clinical consequences.

Reference:
Bissonnette R, Vender R, Pinter A, et al. The hf-PGA is a valid and reliable measure of hand/foot psoriasis severity in adults: results from a phase 2b clinical trial. J Dermatolog Treat. 2025;36(1):2523373. doi:10.1080/09546634.2025.2523373