Reduction of Inter-Rater and Intra-Rater Variability in Psoriasis Area and Severity Index Assessment by Photographic Training

Background: Severity grading is important for the assessment of psoriasis treatment efficacy. This is most commonly achieved by using the psoriasis area and severity index (PASI), a subjective tool with inherent inter-rater and intra-rater variability. PASI-naive dermatologists require training to properly conduct a PASI assessment. Objective: In the present study, we aimed to investigate whether photographic training improves inter-rater and intra-rater variabilities. We also determined which PASI component has the greatest impact on variability. Methods: Twenty-one dermatologists received 1 hour of PASI training. They were tested before and after the training to evaluate intra-rater variability. The physicians were further tested after training by using a reference photograph. Results: The mean of each PASI component was underevaluated compared with scoring by a PASI expert. The concordance rate with the expert's grading was highest for thickness followed by erythema, scaling, and area. The scaling score showed the greatest improvement after training. After training, the distribution of deviation from the expert's grading, which signifies inter-rater variability, improved only for the PASI area component. The deviation of scaling grading improved upon retesting by using a reference photograph. Conclusion: PASI assessment training improved variabilities to some degree but not for every PASI component. The development of an objective psoriasis severity assessment tool will help overcome the subjective variabilities in PASI assessment, which can never be completely eliminated via training.