Evaluation of Skindex-16 construct validity in routinely collected psoriasis data: a retrospective analysis of the relationship between overall physician global assessment scores and Skindex-16 and measure discordance

Abstract

Patient-reported outcome measures (PROMs) capture disease severity metrics from the patient's perspective, including health-related quality of life (HRQL). Disease-specific validation of PROMs improves their clinical utility. We evaluated construct validity (HRQL) for Skindex-16 in routinely seen psoriasis patients and characterized instances of discordance between Skindex-16 scores and clinician-reported outcome measure of disease severity. We retrospectively studied psoriasis patients seen by University of Utah Dermatology from 2016 to 2020. Cross-sectional construct validity was assessed using quantile regression and Spearman correlation between overall physician global assessment (OPGA) score and Skindex-16 scores. Longitudinal within-subject correlation was performed using linear mixed models. Discordance (10th percentile or lower OPGA and 90th percentile or higher Skindex-16 score [clear skin, poor HRQL; cspHRQL] or the reverse [severe skin, good HRQL; ssgHRQL]) was characterized descriptively. 681 first-visit patients with psoriasis were included. Median overall Skindex-16 score varied by ≥ 10 points across all levels of OPGA scores. OPGA and Skindex-16 domain scores were moderately correlated (emotions ρ = 0.54, functioning ρ = 0.47, and symptoms ρ = 53). Longitudinal correlations were similar (emotion ρ_xy = 0.54, functioning ρ_xy = 0.65, symptoms ρ_xy = 0.47). Visits with cspHRQL discordance occurred for each Skindex-16 domain (emotions = 7, functioning = 13, symptoms = 12). The ssgHRQL group was observed within the emotions (n = 1) and functioning (n = 23) domains. Median Skindex-16 scores are different between different levels of OPGA and show moderate cross-sectional and longitudinal correlation. This supports construct validity in patients with psoriasis. Severe discordance was rare and most often for those with clear skin but poor HRQL. These discordances can prompt further patient-clinician conversation.

Keywords: Dermatology; Overall physician global assessment; Patient-reported outcomes; Psoriasis; Quality of life; Shared decision making; Skindex-16.