Grimace Scores: Research-used Instruments to Assist in the Identification of Pain in Mammals

Sarah Clutton^*
*Correspondence: Sarah Clutton, Department of Veterinary Clinical and Diagnostic Science, University of Calgary, Calgary, Canada, Email:

Keywords

Grimace scores • Pain assessment • Mammals • Facial expressions

Introduction

Pain assessment in mammals, particularly in non-verbal species, presents significant challenges. Traditional methods often rely on behavioral and physiological indicators, which can be subjective and invasive. The advent of grimace scores has revolutionized this domain by offering a reliable, non-invasive means of assessing pain through the analysis of facial expressions. This approach, rooted in the understanding that pain manifests in observable facial changes, has gained traction in both research and clinical settings [1]. Grimace scores were first systematically developed for laboratory rodents, and their success has spurred adaptations for other species, including rabbits, horses, and even non-human primates. The objective nature of these scores makes them particularly valuable in research, where consistent and reproducible measures are essential. This article aims to provide an in-depth examination of grimace scores, tracing their development, application, and impact on animal welfare and pain management [2].

Literature Review

The foundation of grimace scores lies in the ethological observation that facial expressions can serve as reliable indicators of emotional and physical states. Charles Darwin's seminal work, "The Expression of the Emotions in Man and Animals," laid the groundwork for understanding facial expressions as a window into internal states. Building on this, modern researchers have identified specific facial action units that correlate with pain. The Mouse Grimace Scale (MGS), developed by Langford et al. in 2010, was the pioneering effort in this field. The MGS identified five key facial action units: orbital tightening, nose bulge, cheek bulge, ear position, and whisker change. Subsequent studies validated the MGS, demonstrating its reliability and reproducibility across different strains and pain models [3].

Following the success of the MGS, similar scales were developed for other species. The Rabbit Grimace Scale (RbtGS), Horse Grimace Scale (HGS), and Rat Grimace Scale (RGS) are notable examples. These scales have been subjected to rigorous validation studies, confirming their utility in both acute and chronic pain models. The adaptation of grimace scales to various species underscores their versatility and broad applicability. Despite their success, grimace scores are not without limitations. One challenge is the potential for inter-observer variability, which can be mitigated through training and standardized protocols. Additionally, the expression of pain through facial changes can be influenced by factors such as species, strain, and individual differences. Nonetheless, the overall consensus in the literature supports the efficacy of grimace scores as a valuable tool for pain assessment [4].

Discussion

The adoption of grimace scores in research and veterinary practice represents a significant advancement in the field of pain assessment. These scores offer several advantages over traditional methods. Firstly, they are non-invasive, reducing the stress and discomfort associated with other pain assessment techniques. This is particularly important in research settings, where minimizing animal suffering is a key ethical consideration. Secondly, grimace scores provide an objective measure of pain, which enhances the reliability and reproducibility of research findings. This is crucial for studies involving animal models of human diseases, where consistent pain assessment is essential for evaluating the efficacy of treatments and interventions. The use of grimace scores can also improve the welfare of laboratory animals by enabling more accurate and timely pain management [5].

In veterinary practice, grimace scores offer a valuable tool for diagnosing and monitoring pain in patients who cannot verbally communicate their discomfort. This is especially relevant for species with subtle or ambiguous behavioral indicators of pain. By providing a clear and quantifiable measure of pain, grimace scores can guide treatment decisions and improve outcomes for animal patients. Despite these benefits, the implementation of grimace scores faces several challenges. One issue is the need for species-specific validation studies to ensure the accuracy and reliability of the scales. Additionally, the training and standardization required for observers to accurately score facial expressions can be resource-intensive. There is also a need for further research to explore the potential influence of factors such as age, sex, and environmental conditions on grimace scores. Another important consideration is the integration of grimace scores with other pain assessment methods. While facial expressions provide valuable information, a comprehensive approach to pain assessment should incorporate multiple indicators, including behavioral and physiological measures. This holistic approach can enhance the accuracy and sensitivity of pain detection, leading to better outcomes for animals in both research and clinical settings [6].

Conclusion

Grimace scores have emerged as a powerful tool for the assessment of pain in mammals. Their development and validation across multiple species highlight their potential to transform pain management in both research and veterinary practice. By providing a non-invasive, objective, and reliable measure of pain, grimace scores offer significant advantages over traditional methods. The success of grimace scores underscores the importance of ongoing research and collaboration in this field. Continued efforts to validate and standardize these scales across different species, strains, and conditions will enhance their utility and applicability. Additionally, integrating grimace scores with other pain assessment methods can provide a more comprehensive understanding of pain and improve outcomes for animals.

In conclusion, grimace scores represent a promising advancement in the field of pain assessment. Their adoption has the potential to improve animal welfare, enhance the reliability of research findings, and guide effective pain management strategies. As the field continues to evolve, further research and innovation will be crucial in realizing the full potential of grimace scores and advancing our understanding of pain in animals.

Acknowledgement

None.

Conflict of Interest

None.

References

1. Leach, Matthew C., Claire A. Coulter, Claire A. Richardson and Paul A. Flecknell. "Are we looking in the wrong place? Implications for behavioural-based pain assessment in rabbits (Oryctolagus cuniculi) and beyond?." PloS One 6 (2011): e13347.

Google Scholar, Crossref, Indexed at

2. Defensor, Erwin B., Michael J. Corley, Robert J. Blanchard and D. Caroline Blanchard. "Facial expressions of mice in aggressive and fearful contexts." Physiol Behav 107 (2012): 680-685.

Google Scholar, Crossref, Indexed at

3. Long, Hu, Lina Liao, Meiya Gao and Wenqiang Ma, et al. "Periodontal CGRP contributes to orofacial pain following experimental tooth movement in rats." Neuropeptide 52 (2015): 31-37.

Google Scholar, Crossref, Indexed at

4. Jirkof, Paulin, Thea Fleischmann, Nikola Cesarovic and Andreas Rettich, et al. "Assessment of postsurgical distress and pain in laboratory mice by nest complexity scoring." Lab Anim 47 (2013): 153-161.

Google Scholar, Crossref, Indexed at

5. Oliver, Vanessa, Debbie De Rantere, Rheanne Ritchie and Jessica Chisholm, et al. "Psychometric assessment of the Rat Grimace Scale and development of an analgesic intervention score." PLoS One 9 (2014): e97882.

Google Scholar, Crossref, Indexed at

6. Ellen, Yvette, Paul Flecknell and Matt Leach. "Evaluation of using behavioural changes to assess post-operative pain in the guinea pig (Cavia porcellus)." PloS one 11 (2016): e0161941.

Google Scholar, Crossref, Indexed at