Trigeminal Nerve Asymmetry in Horses With Idiopathic Trigeminal-Mediated Headshaking: A Retrospective Case-Control Magnetic Resonance Imaging Study.
Authors: Heun Frederik, Delarocque Julien, Feige Karsten, Hellige Maren
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Trigeminal Nerve Asymmetry in Equine Headshaking Idiopathic trigeminal-mediated headshaking (ITMHS) remains a frustrating diagnosis in equine practice, with limited diagnostic tools beyond clinical observation; this retrospective MRI study tested whether the condition involves detectable structural changes to the trigeminal nerve itself, drawing on evidence from human neurology where nerve atrophy produces measurable asymmetry. Using high-field 3-Tesla MRI, researchers measured trigeminal nerve cross-sectional area (TNCSA) at four defined points along the nerve in 20 horses with ITMHS and six unaffected controls, quantifying side-to-side differences whilst accounting for body-weight variation. Horses with ITMHS demonstrated 4.1 to 7.6-fold greater trigeminal nerve asymmetry than controls (p < 0.001), with excellent measurement repeatability and preliminary cut-off values established to distinguish affected from unaffected horses. These findings suggest ITMHS involves unilateral or asymmetric trigeminal nerve pathology rather than purely functional dysfunction, potentially opening avenues for targeted interventions beyond current symptomatic management and justifying MRI as a diagnostic tool in cases where diagnosis remains uncertain—though clinicians should note this was a relatively small retrospective cohort and the clinical significance of detected asymmetry warrants further investigation.
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Practical Takeaways
- •MRI-detected trigeminal nerve asymmetry is a potential diagnostic marker for ITMHS and may help differentiate this condition from other causes of headshaking in practice
- •The unilateral or asymmetric nature of trigeminal nerve disease in ITMHS horses suggests future targeted therapeutic interventions may be possible
- •Establishing MRI cut-off values for trigeminal nerve asymmetry could provide a non-invasive, objective diagnostic tool to supplement clinical evaluation of horses with suspected ITMHS
Key Findings
- •Horses with ITMHS demonstrated 4.1 to 7.6-fold greater trigeminal nerve cross-sectional area asymmetry compared to control horses (F(3,70) = 11.271, p < 0.001)
- •Trigeminal nerve asymmetry was detectable via 3-Tesla MRI and showed excellent measurement repeatability
- •Absolute trigeminal nerve cross-sectional area did not differ significantly between ITMHS and control groups but was influenced by body weight
- •Tentative cut-off values for trigeminal nerve cross-sectional area asymmetry could discriminate between ITMHS-affected and control horses