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. 2019 Dec 13;9(1):19128.
doi: 10.1038/s41598-019-55693-8.

Facial expressions of pain in cats: the development and validation of a Feline Grimace Scale

Marina C Evangelista  1 , Ryota Watanabe  1 , Vivian S Y Leung  1   2 , Beatriz P Monteiro  1 , Elizabeth O'Toole  1 , Daniel S J Pang  1   2   3 , Paulo V Steagall  4
Affiliations

Facial expressions of pain in cats: the development and validation of a Feline Grimace Scale

Marina C Evangelista et al. Sci Rep. .

Abstract

Grimace scales have been used for pain assessment in different species. This study aimed to develop and validate the Feline Grimace Scale (FGS) to detect naturally-occurring acute pain. Thirty-five client-owned and twenty control cats were video-recorded undisturbed in their cages in a prospective, case-control study. Painful cats received analgesic treatment and videos were repeated one hour later. Five action units (AU) were identified: ear position, orbital tightening, muzzle tension, whiskers change and head position. Four observers independently scored (0-2 for each AU) 110 images of control and painful cats. The FGS scores were higher in painful than in control cats; a very strong correlation with another validated instrument for pain assessment in cats was observed (rho = 0.86, p < 0.001) as well as good overall inter-rater reliability [ICC = 0.89 (95% CI: 0.85-0.92)], excellent intra-rater reliability (ICC > 0.91), and excellent internal consistency (Cronbach's alpha = 0.89). The FGS detected response to analgesic treatment (scores after analgesia were lower than before) and a cut-off score was determined (total pain score > 0.39 out of 1.0). The FGS is a valid and reliable tool for acute pain assessment in cats.

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Conflict of interest statement

Dr. Paulo Steagall has received speaker honoraria and provided consultancy services to Zoetis. Dr. Beatriz Monteiro has provided consultancy services to Zoetis. As a sponsor of the study, Zoetis reviewed the proposal and approved the study design, but it was not involved with manuscript publication. This does not alter the authors’ adherence to Scientific Reports policies on sharing data and materials.

Figures

Figure 1
Figure 1
(a) Video-recording of cats. A wide-angle lens camera was placed between the cage bars and cats were video-recorded undisturbed for 6 min. (b) Image cropping and selection. Files were downloaded on to a computer and screenshots obtained from video-recordings.
Figure 2
Figure 2
(a) Measured distances for the ears, eyes and muzzle. A - Ears: tip to tip; B - Ears: base to base; C - Eye: height; D - Eye: width; E - Muzzle: height; F - Muzzle: width. Eyes and muzzle distances were measured bilaterally and averaged. (b) Measured ear angles. M - Medial angle: between the medial border of the ear and top of the head; L - Lateral angle: between the lateral border of the ear and an imaginary line connecting both marginal cutaneous pouches. Angles were measured bilaterally and averaged.
Figure 3
Figure 3
Flowchart of the animals included in the study. Blue boxes = control cats included for: adevelopment and bvalidation of the Feline Grimace Scale (FGS). Red boxes = client-owned cats included for: adevelopment and bvalidation of the FGS.
Figure 4
Figure 4
Boxplot showing median (solid line) and interquartile ranges for Feline Grimace Scale (FGS) scores in control (n = 20) and painful cats (n = 28). The whiskers represent the range. The FGS scores were higher for painful than control cats (Mann-Whitney U test, *p < 0.001).
Figure 5
Figure 5
(a) Boxplot showing median (solid line) and interquartile ranges for Feline Grimace Scale (FGS) scores in control cats (n = 20). The FGS scores did not change for control cats after 1 h (without treatment; Wilcoxon signed rank test, p = 0.342). (b) Boxplot showing median (solid line) and interquartile ranges for FGS scores in painful cats (n = 15). The FGS scores decreased in painful cats after analgesia (Wilcoxon signed rank test, *p = 0.003).
Figure 6
Figure 6
Scatterplot showing correlation between Feline Grimace Scale (FGS) and Glasgow composite measure pain scale for acute pain in cats (rCMPS-F) scores (Spearman’s rho = 0.86, p < 0.001) from control (n = 20) and client-owned cats (n = 35).
Figure 7
Figure 7
(a) Receiver operating characteristics (ROC) curve showing the cut-off point >0.39 for rescue analgesia, with sensitivity of 90.7%, and specificity of 86.6%. The area under the curve (AUC) of 0.94 (95% CI: 0.89–0.98), represents high accuracy of the Feline Grimace Scale (FGS). (b) Scatterplots showing the FGS scores and cut-off point for rescue analgesia (0.39), identified from the ROC curve analysis. N = 110 images of cats’ faces were classified as “absence of pain (0)” or “presence of pain (1)” according to Glasgow composite measure pain scale for acute pain in cats (rCMPS-F) scores.
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