Just How Effective is the Mouse Grimace Scale?
09 Oct 2015

The Mouse Grimace Scale needs further research before it can be considered an effective tool for routine pain assessment in laboratory animals, according to recent study in PLOS One. The study found that baseline (non-painful) scores varied significantly between the some strains and sexes of laboratory mice, indicating that consistency is potentially dependent on having baseline scores for any animal being assessed for pain.

The MGS or Mouse Grimace Scale was developed in 2010 by researchers from McGill University as a way to help researchers measure the effectiveness of new drugs. The scale potentially assesses pain in mice through changes in five facial units: orbital tightening (eye squinting), nose bulge, cheek bulge, ear position, and whisker changes. Additionally, it requires minimal training for the observer to be effective.

The scale was developed as a research tool, but there has been increasing interest about it's use as a cage-side clinical assessment tool. "To date, the MGS has always been utilized in a research setting, where baseline MGS scores are compared to those following a potentially painful procedure within each individual animal. Additionally, these scores have always been carried out retrospectively from still images," one of the study's authors, Amy Miller of Newcastle University, told ALN exclusively.


During the study, the researchers performed the MGS on mice to see if they could find a consistent baseline scale between individuals. "In our study, we aimed to determine if baseline MGS scores for mice (i.e. those not in pain) were comparable between cohorts, strains and the two sexes. Additionally we aimed to determine if scores were comparable when made either retrospectively from still images or live at the cage-side. If baseline scores are shown to be consistent, then the MGS could be potentially used in live clinical scenarios to assess pain in mice when baseline scores are not available as a comparator," Miller continued.

However, the results showed great variation. "Our results indicate that baseline MGS scores vary significantly between both strains and sexes of mice. Additionally, the method used to score the MGS score (i.e. live at the cage side vs retrospectively from still images) results in a significantly different overall MGS scores," she added.

The study's authors cautions that further research is needed before the Mouse Grimace Scale can be used as a clinical tool for routine pain assessment due to the levels of variation found by the study. "Those who wish to use the MGS or any of the other grimaces scales developed so far should do so alongside other established pain assessment techniques until the Grimace Scales can be further validated," Miller concluded.