Global assessment of psoriasis severity and change from photographs: a valid and consistent method

Five raters tested the validity and consistency of global assessments of severity and change from standardized photographs in 30 consecutive patients with plaque psoriasis. The main outcome measures were physician global assessment (PGA) scores for change between baseline and follow-up visits ("dynamic PGA") and for severity at the baseline visit ("static PGA"). These photographic evaluation scores were compared with in-person clinical ratings. Panel ratings were obtained using the mean of the five raters' independent evaluations from photographs. Validity and consistency were assessed with intra-class coefficients (ICCs; 95% confidence interval). Intra-rater and intra-panel consistencies for photographic dynamic PGA scores were 0.85 (0.74-0.92) and 0.95 (0.92-0.99), respectively. As an evaluation of validity, agreement between photographic and clinical static PGA scores was 0.87 (0.75-0.93). We concluded that global assessment of psoriasis severity and change from photographs by a panel of experts was accurate and consistent. The generalizability of the results requires further studies. The intrinsic limitations of photographic assessment of individual characteristics such as plaque thickness and their effect on global photographic assessment should be further evaluated.