History, Rest and Exercise Score (HRE-S) for assessment of disease severity in horses with trigeminal-mediated headshaking

Background: In horses with trigeminal-mediated headshaking (TMHS), clinical signs are likely to be expression of neuropathic facial pain. Currently, subjective assessment of disease severity is used as measure of compromise of animal's welfare.

Objectives: To develop and validate a precise scoring system for TMHS: History, Rest and Exercise Score (HRE-S). The HRE-S consists of three subscores: history score (H-S), resting score (R-S) and exercise score (E-S).

Study design: Retrospective observational study.

Methods: Seven masked observers with different experience used HRE-S to score 40 video recordings taken during rest and lungeing including five duplicates. Video recordings were taken from nine horses with TMHS and three controls. Inter- and intraobserver reliability and practicability of HRE-S were assessed. For every video recording severity of clinical signs was graded by every observer using an intuitive global-type-scale and interobserver reliability was calculated. Convergent validity was evaluated comparing HRE-S to groups created by an existing score (grade 0-3). Discriminant validity was analysed comparing HRE-S to groups created by intuitive global-type-scale.

Results: Reliability for HRE-S was excellent, irrespective of observers experience: Spearman's Rho = 0.946, p < 0.001 (intraobserver reliability) and intraclass correlation coefficient = 0.98, p < 0.001 (interobserver reliability). Interobserver reliability for intuitive global-type-scale was fair to substantial: Fleiss' κappa = 0.48 (R-S) -0.63 (E-S). Groups created by intuitive global-type-scale had significantly different R-S and E-S (p < 0.05), demonstrating discriminant validity. Convergent validity was proven as horses with grade 3/3 had significantly higher average E-S and total scores compared with an existing score than those with grade 0/3 or 1/3 (p < 0.001).

Main limitations: Retrospective nature, video recordings, sample size.

Conclusions: HRE-S is a valid and reliable score evaluating disease severity in TMHS, independent of observers' experience.