Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases.
Authors: Newton S A, Knottenbelt D C, Eldridge P R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Headshaking in Horses — A Trigeminal Nerve Disorder Twenty horses presenting with chronic idiopathic headshaking were subjected to diagnostic nerve blocks targeting branches of the trigeminal nerve, alongside imaging and endoscopy, to establish potential aetiological mechanisms. Posterior ethmoidal nerve anaesthesia produced 90–100% improvement in 65% of cases, whereas infraorbital blocks were ineffective, suggesting involvement of more proximal trigeminal branches rather than peripheral irritation. Pharmaceutical intervention proved most promising: carbamazepine alone achieved 88% efficacy, whilst combined cyproheptadine and carbamazepine produced 80–100% improvement in 80% of cases; by contrast, tinted contact lenses showed no sustained benefit, effectively ruling out photophobia as a primary mechanism in this cohort. The clinical and therapeutic response profile aligns closely with trigeminal neuralgia in humans, indicating that equine headshaking likely represents a trigeminal neuritis or neuralgia rather than an environmental sensitivity or anatomical obstruction. For practitioners, this research offers a rational diagnostic pathway and suggests that whilst complete resolution remains elusive, carbamazepine-based therapy can provide meaningful symptomatic control—though dosing protocols require refinement and individual responses remain variable, necessitating careful monitoring and potentially combination approaches in treatment-resistant cases.
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Practical Takeaways
- •Headshaking in horses is likely due to trigeminal neuritis/neuralgia; carbamazepine therapy can control but not cure the condition, requiring ongoing management
- •Diagnostic perineural anaesthesia of the posterior ethmoidal nerve is a useful test to confirm trigeminal involvement and may guide treatment decisions
- •Photophobia is unlikely to be the primary cause in most headshaking cases, so tinted lenses should not be relied upon as a primary treatment strategy
Key Findings
- •Posterior ethmoidal nerve anaesthesia produced 90-100% improvement in 65% of cases (11/17), compared to no effect in 6/7 cases of infraorbital anaesthesia
- •Carbamazepine alone was effective in 88% of cases, and carbamazepine combined with cyproheptadine resulted in 80-100% improvement in 80% of cases
- •Tinted contact lenses showed no long-term benefit, with only 2 cases showing transient improvement, suggesting photic aetiology is unlikely
- •Clinical response pattern to carbamazepine and positive response to posterior ethmoidal nerve anaesthesia strongly suggests trigeminal nerve involvement as the underlying aetiopathology