Pain Assessment of Horses With Trigeminal-Mediated Headshaking (TMHS) at Rest Between Episodes.
Authors: Franzen Vanessa, Reisbeck Daniela, Leibl Yvonne, Schoster Angelika, May Anna
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Pain Assessment in Trigeminal-Mediated Headshaking Whilst clinicians have long recognised that horses with trigeminal-mediated headshaking (TMHS) experience acute pain during episodes, little is known about their pain state during the asymptomatic periods between attacks—a gap this study addresses through systematic facial pain assessment. Researchers evaluated 60 horses across three groups (20 with TMHS at rest, 20 with colic, 20 healthy controls) using the Horse Grimace Scale applied to standardised facial photographs by nine independent examiners with varying levels of HGS experience and veterinary training. TMHS horses demonstrated significantly elevated median HGS scores of 5.6 (range 2.4–7.4) compared to healthy horses at 1.2 (0.1–2.4), approaching the scores of acutely colicky horses at 6.6 (3.8–8.4), with consistent differences across all facial action units measured. These findings suggest that severely affected TMHS horses exist in a persistent pain state between attacks rather than returning to painlessness, fundamentally challenging current assumptions about the disease and raising important questions about quality of life that should inform individual clinical decision-making around prognosis, management strategies, and welfare considerations for this condition.
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Practical Takeaways
- •TMHS should not be considered a condition limited to active episodes; severely affected horses experience measurable pain between attacks that warrants quality-of-life assessment
- •Facial grimacing patterns (HGS scoring) can be used as a clinical tool to evaluate resting pain in TMHS horses, though examiners require training for reliable interpretation
- •Management decisions for TMHS cases should consider inter-episode pain and individual quality-of-life evaluation rather than only addressing acute attack episodes
Key Findings
- •TMHS horses showed median Horse Grimace Scale scores of 5.6 (range 2.4-7.4) at rest between episodes, significantly higher than healthy controls (1.2, range 0.1-2.4; p<0.05)
- •All facial action units showed statistically significant differences between healthy, TMHS, and colic groups (p<0.05)
- •TMHS horses demonstrated pain signatures during absence of clinical headshaking attacks, suggesting inter-episode pain in severely affected individuals
- •Pain assessment consistency varied by examiner experience, with experienced HGS users providing more reliable evaluations than those without prior training