Measurement properties of the product of investigator's global assessment and body surface area in children and adults with atopic dermatitis.

BACKGROUND: Multiple clinician-reported outcome measures exist for atopic dermatitis (AD) severity. However, there is no gold standard for use in clinical practice. OBJECTIVES: To determine the measurement properties of the product of validated Investigator's Global Assessment for AD (vIGA) and body surface area (BSA) overall or divided into six categories (cBSA: 0%/0.1, <10%/10, <30%/30, <50%/50, <70%/70 and <90%/90-100%) and compare with other clinician-reported and patient-reported outcomes in adults and children with AD. METHODS: We performed a prospective dermatology practice-based study using questionnaires and evaluation by a dermatologist (n = 653). RESULTS: vIGA*BSA and vIGA*cBSA had good convergent validity with BSA (Spearman's ρ = 0.97 and 0.93), eczema area and severity index (ρ = 0.94 and 0.92), and objective SCORAD (ρ = 0.88 and 0.89); and weak-to-good convergent validity with Numeric Rating Scale average itch (ρ = 0.22 and 0.22) and worst itch (ρ = 0.27 and 0.28), Patient-Oriented Eczema Measure (ρ = 0.44 and 0.43), Dermatology Life Quality Index (ρ = 0.48 and 0.49), ItchyQOL (ρ = 0.45 and 0.46), PROMIS Sleep Disturbance (ρ = 0.46 and 0.37) and sleep-related impairment (ρ = 0.31 and 0.31) in adults and/or children; very good discriminant validity for physician-reported global AD severity; good responsiveness to change of severity of AD and itch; and good reliability (intraclass correlation coefficient [95% confidence interval]: 0.72 [0.60-0.81] and 0.74 [0.62-0.82]) with no floor or ceiling effects. Thresholds for interpretability bands and clinically important difference were established. CONCLUSIONS: vIGA*BSA and vIGA*cBSA scores showed good convergent and discriminant validity, reliability, responsiveness and interpretability in adults and children with AD, and were feasible for use in clinical practice. vIGA*BSA and vIGA*cBSA had slightly lower convergent validity than EASI or objective SCORAD, but might be more efficient to collect and score.