Hair density response to photobiomodulation in canine alopecia X is measured reliably with an ordinal scale: a randomized, controlled, double-blind study.

Abstract

Objective: To develop an ordinal hair density score (HDS), determine its inter-rater agreement, and use it in a trial of photobiomodulation as a sole treatment for alopecia X.

Methods: A 5-level ordinal HDS system was developed. Four blinded veterinary dermatologists independently graded a 50-image reference set using the HDS. Inter-rater agreement was assessed using the quadratic-weighted Fleiss κ, Brennan-Prediger, and Gwet AC2 coefficients. A double-blind, randomized, controlled trial was performed using a convenience sample of alopecia X dogs recruited based on inclusion and exclusion criteria over 16 months. Photoconverter gels were applied on both alopecic sides of each patient once per week for 8 weeks. One randomly chosen side was exposed to excitatory light (active treatment) but not the other (sham). Skin biopsies were taken from the center of each treated side before and at the end of the study. The images of active and sham sides acquired before the study, at day 50, and at the end of the study were graded using the HDS.

Results: Inter-rater agreement coefficients were greater or equal to 0.81. Seven dogs were enrolled, but 1 withdrew after day 50. Hair density score evolved over time in both sides, but the OR of improved HDS increased with time only for the 3 central HDS grades. Histopathology revealed no notable differences between sides and across time.

Conclusions: The HDS seems valid and useful in assessing the effect of photobiomodulation on the exposed areas of our alopecia X patients.

Clinical relevance: This novel, easily applicable scale may facilitate the therapeutic monitoring of alopecia in dogs.