Validation of the Equine Urticaria Activity Score for the assessment of chronic recurrent urticaria in horses.

Background: Recurrent urticaria is common in horses. The pathophysiology is poorly understood and treatment options are limited. Often, only glucocorticoids are effective for controlling clinical signs, albeit with potential adverse effects. Studies investigating new treatments need a validated objective scoring system for the grading of skin lesions to assess response.

Hypothesis/objectives: The aims were to investigate inter- and intraobserver reliability of the Equine Urticaria Activity Score (EqUAS) for the grading of skin lesions in horses with recurrent urticaria, and to examine agreement between experienced and inexperienced observers.

Animals: Forty privately owned horses enrolled in a therapeutic clinical trial.

Materials and methods: Ten standardised photographs of both sides of the body of each horse were used to create 40 individual datasets. Five masked observers graded the photographs according to the EqUAS for calculation of interobserver reliability. Intraobserver reliability was calculated from two observers each grading the photographs twice. Scores were evaluated for reliability with Pearson's correlation (r) and for agreement with the intraclass correlation coefficient (ICC).

Results: Interobserver reliability was excellent with r = 0.9036-0.9600 (p < 0.0001). Intraobserver reliability and agreement also were excellent with r = 0.98 for each observer (p < 0.0001) and ICC = 0.945. Correlation and agreement between experienced and inexperienced observers were excellent (r = 0.9615 [p < 0.0001] and ICC = 0.941).

Conclusions and clinical relevance: The EqUAS showed excellent intra- and interobserver reliability for the evaluation of skin lesions of horses with chronic recurrent urticaria. It can be a useful tool in clinical studies.