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

Objectives This study investigated inter-rater reliability, agreement and responsiveness of the Feline Grimace Scale (FGS) scores in brachycephalic cats. Methods Twenty-eight brachycephalic cats (6.6 ± 4.4 years; 4.2 ± 1.0 kg) undergoing ocular surgery were included in a prospective, randomized, blinded study. Ninety-five 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 (LoA) 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). Generalized linear mixed models evaluated responsiveness (P <0.05). Results Inter-rater reliability (ICCsingle; 95% confidence intervals) was poor for muzzle tension (0.47; 0.36–0.58) and whiskers change (0.34; 0.22–0.46), good for ear (0.81; 0.74–0.86) and eye position (0.84; 0.79–0.88), moderate for head position (0.71; 0.59–0.79) and excellent for FGS total ratio scores (0.92; 0.89–0.94). LoA ranged from -0.37 to 0.22 with bias of -0.08 suggesting that some cats could have their scores affected in comparison with real-time scores. 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.