Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases.

This research focuses on investigating the possible cause and treatments for headshaking in horses. It suggests that a condition similar to human trigeminal neuralgia, affecting a specific nerve in the horse’s head, may be responsible. The medication carbamazepine showed promise in managing the condition, though cure remains elusive.

Study Sample and Procedures

• The research involved twenty mature horses that had been showing signs of typical headshaking between 2 weeks to 7 years period.
• Each horse underwent a clinical examination, including radiography of the head and nasopharyngeal endoscopy. They were observed at rest and during exercise, both before and after several interventions.
• The interventions included the application of an occlusive nasal mask, tinted contact lenses, and the perineural anaesthesia of the infraorbital and posterior ethmoidal branches of the trigeminal nerve.

Outcome of Interventions

• Infraorbital anaesthesia showed no effect in the majority of cases. However, posterior ethmoidal nerve anaesthesia appeared promising, showing substantial improvement in 65% of the cases.
• Tinted contact lenses demonstrated no long-term benefit, with only two cases showing a transient improvement.
• The study found no evidence supporting a photic (light-based) cause of the headshaking in horses.

Treatment Success and Conclusions

• Treatments were designed based on the results of the diagnostic methods. One such method was sclerosis (hardening) of the posterior ethmoidal branch of the trigeminal nerve. While this had temporary benefits, it wasn’t a definitive solution.
• Medication trials with cyproheptadine and carbamazepine were conducted. Cyproheptadine alone didn’t produce any significant results. However, when combined with carbamazepine, there was noticeable improvement noted in a majority of the cases.
• Carbamazepine on its own was effective in 88% of cases. However, its effectiveness was unpredictable at pre-set doses.
• Based on the positive outcomes following carbamazepine treatment, and given the clinical characteristics of the headshaking, the researchers suggest the possible involvement of the trigeminal nerve in the condition.
• They conclude that a condition similar to human trigeminal neuralgia might be an underlying cause of equine headshaking. They also open up avenues for further research, encompassing a detailed investigation of dosages, duration of effectiveness, and other effects of carbamazepine treatment.