It is not known which objective disease extent measure for atopic dermatitis is the most reliable. This study compared the inter-rater and intra-rater reliability of the four most commonly used outcome measures for atopic dermatitis: the objective SCORing Atopic Dermatitis (SCORAD), Eczema Area and Severity Index (EASI), Six Area, Six Sign Atopic Dermatitis (SASSAD) and Three Item Severity index (TIS), as well as analysing their correlation to three QOL instruments: the Patient-Orientated Eczema Measurement, Child/Dermatology Life Quality Index and SkinDex-29.
After power calculations, 12 atopic dermatitis patients having different degrees of severity were assessed on the same day by 5 independent trained dermatology assessors. Reliability was measured using the intra-class correlation coefficient calculated through one-way random effect ANOVA and Bland-Altman plots. Correlation between subjective and objective outcome measures was computed using the two-tailed Spearman’s rho correlation with scatterplots.
EASI demonstrated a high intra-rater and moderate inter-rater reliability, ICC=0.886 (95% CI: 0.744-0.952) and ICC=0.73 (95% CI=0.5 – 0.9), respectively. SASSAD showed moderate intra-rater and inter-rater reliabilities, ICC=0.720 (95% CI = 0.424-0.878) and ICC=0.68 (95% CI=0.44-0.88). TIS showed high intra-rater reliability ICC=0.886 (95% CI: 0.744-0.952) but low inter-rater reliability ICC=0.497 (95% CI=0.233–0.785). Objective SCORAD showed low intra-rater and inter-rater reliability, with ICC of 0.446 (95%CI=0.037-0.730) and 0.498 (95% CI= 0.234–0.785), respectively. Only SASSAD demonstrated moderate correlation with SkinDex-29 ρ=0.611 (p=0.035).
In conclusion, this study found that the EASI score was the most reliable objective outcome measure and supports the use of EASI as a routine extent measure for atopic dermatitis studies and possibly for routine clinical use.