Client-specific outcome measure for chronic osteoarthritis pain assessment in horses

Introduction Osteoarthritis (OA) is a prevalent cause of chronic pain and lameness in horses. Whereas lameness can be quantified using objective measures, the assessment of OA-associated pain remains challenging. This study aimed to evaluate the applicability of the Client-Specific Outcome Measure (CSOM), a tool widely used in small animals, for the assessment of chronic OA pain in horses through caretaker evaluation. Methods Seventeen privately owned horses with confirmed OA were enrolled in a 20-week randomized, double-blind, placebo-controlled study. For each horse, three individual pain-related indicators (CSOM items) were identified through a veterinarian–caretaker consultation. The selected items were regularly scored (0–4), and the scores were summed to obtain a total CSOM score (CSOM-sum). The CSOM-sum was compared with other pain assessment measures, including a caretaker-assigned visual analogue scale (VAS-own), a veterinarian-assigned visual analogue scale (VAS-exp), subjective lameness scores, and a gait asymmetry index. Results The CSOM-sum showed moderate but significant correlations with all other pain and lameness measures (rₛ = 0. 49–0. 60, p 0. 05). In particular, CSOM-sum correlated with gait asymmetry (rₛ = 0. 434, p 0. 0001) ; subgroup analysis revealed a moderate correlation in treated horses (rₛ = 0. 4539, p = 0. 0025) and a higher correlation in controls (rₛ = 0. 5536, p = 0. 0006). The VAS-own and VAS-exp scores showed good overall agreement (bias = −4. 76 mm; ICC = 0. 727; ICCT = 0. 625; ICCC = 0. 838), although with relatively wide limits of agreement. The internal consistency of the CSOM items was high (Cronbach’s α = 0. 81 overall; αT = 0. 787; αC = 0. 890). Discussion These findings indicate that, provided relevant items are carefully identified, the CSOM may represent a valuable complementary tool for assessing and monitoring pain severity in horses under field conditions.