Challenges using the Feline Grimace Scale in brachycephalic cats with ocular pain

Objectives This study investigated the inter-rater reliability, agreement and responsiveness of the Feline Grimace Scale (FGS) in brachycephalic cats. Methods A total of 28 brachycephalic cats (mean age 6.6 ± 4.4 years, mean weight 4.2 ± 1.0 kg) undergoing ocular surgery were included in a prospective, randomised, blinded study. Cats presenting fear-anxiety behaviours were not enrolled. In total, 95 images of these cats were collected from video recordings pre- and postoperatively (before/after analgesia), scored by four raters using the FGS and compared with real-time scores. Limits of agreement (LoAs) and bias were evaluated using the Bland–Altman method (good or poor agreement if bias <0.1 or >0.1, respectively). Inter-rater reliability was assessed using the intraclass correlation coefficient (ICC; <0.50 = poor, 0.50–0.75 = moderate, 0.76–0.90 = good and >0.90 = excellent reliability). Generalised linear mixed models evaluated responsiveness ( P <0.05). Results Inter-rater reliability (ICC single ) was poor for muzzle tension (0.47, 95% confidence interval [CI] 0.36–0.58) and whiskers change (0.34, 95% CI 0.22–0.46), good for ear (0.81, 95% CI 0.74–0.86) and eye position (0.84, 95% CI 0.79–0.88), moderate for head position (0.71, 95% CI 0.59–0.79) and good for FGS total ratio scores (0.76, 95% CI 0.68–0.82). LoAs were in the range of –0.37 to 0.22 with a bias of –0.08, suggesting that some cats could have their scores affected in comparison with real-time scores. Mean FGS total scores decreased after analgesia pre- (0.56 ± 0.10 vs 0.38 ± 0.15; P = 0.005) and postoperatively (0.60 ± 0.18 vs 0.36 ± 0.15; P <0.001). Conclusions and relevance The FGS is a responsive pain-scoring instrument in brachycephalic cats with ocular pain, with good agreement and excellent inter-rater reliability for total ratio scores. Pain may be overestimated using image assessment in some brachycephalic cats.