In horses with trigeminal-mediated headshaking, clinical signs are likely to be an expression of neuropathic facial pain. Currently, subjective assessment of disease severity is used as a measure of compromise of the animal’s welfare. The aims of this retrospective observational study were to develop and validate a precise scoring system for trigeminal-mediated headshaking: History, Rest and Exercise Score (HRE-S). The HRE-S consists of three sub scores: history score (H-S), resting score (R-S) and exercise score (E-S).
Seven masked observers with different experience used HRE-S to score 40 video recordings taken during rest and lunging, including five duplicates. Video recordings were taken from nine horses with trigeminal-mediated headshaking and three controls. Inter- and intra-observer 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.
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’ Kappa = 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).
HRE-S is a valid and reliable score evaluating disease severity in trigeminal-mediated headshaking, independent of observers’ experience.