Establishing and Validating an Ichthyosis Severity Index

Abstract

We designed and validated a Visual Index for Ichthyosis Severity for scale and erythema that provides (1) written descriptions of the features characteristic of each level of severity, (2) visual standards for four body sites, and (3) two distinct standards to account for different types of scale. We tested the Visual Index for Ichthyosis Severity for reliability and reproducibility using two different settings: one that utilized scoring of 60 test photographs by 10 dermatologists, and one with in-person evaluations on 85 subjects by 12 dermatologists at the Foundation for Ichthyosis and Related Skin Types conference. The validation process revealed high reliability and reproducibility for both scale and erythema. The interrater and intrarater intraclass correlation coefficients for scale were consistently near or greater than 0.7 in both settings. By contrast, the interrater reliability for erythema was higher during in-person validation compared with validation on test photographs. Our analysis indicates that the Visual Index for Ichthyosis Severity performs better in person than with photographs, an important consideration in the design of clinical trials. Power analysis predicts that a 1-point difference on this 5-step scale would be detectable with 12 subjects in each of two defined groups. This index provides a tool for clinical phenotyping and assessment of therapeutic response for many disorders of keratinization.