Trigeminal-Mediated Headshaking in Horses: A Novel Therapeutic Modality

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A 14-year-old female palomino Paint mare was referred to Cornell to undergo a novel therapeutic treatment for Trigeminal-Mediated Headshaking (TMH). The mare's signs - intermittent paroxysmal headshaking, muzzle rubbing, panic at onset of attacks, and snorting - were first noticed in 2014 and initially described as 'willful misbehavior'. Follow-up by the owner resulted in a diagnosis of TMH by the referring veterinarian through exclusion of other differentials by endoscopy, pharmaceutical trials, and environmental modification. The diagnosis was confirmed via posterior ethmoidal nerve analgesia (PET Block). Trigeminal-Mediated Headshaking in horses is a neuropathic disorder believed to result in sensitization of the caudal nasal nerve (CNN), a division of the maxillary branch of the trigeminal nerve, responsible for conducting sensory information from the nasal mucosa to the CNS. Affected horses have a low threshold to a stimulus or stimuli: the resulting hyperesthesia is believed to cause stimulus that would be insignificant in non-affected horses to be registered as pain in affected horses, provoking sudden, unpredictable, and often violent behavior. Signs can vary in intensity from occasional head shaking to paroxysmal bucking, pawing, and rearing, rendering the animal unfit for work. Frequently this disease results in euthanasia for the safety of the rider, financial, or ethical reasons. This neuropathy is believed to have much in common with the human disorder Trigeminal Neuropathy and so veterinary therapies borrows heavily from experimentation in humans. Several modalities are used to treat this disorder, all of which have low efficacy and high rates of complications. The most promising modality in terms of efficacy and side-effects is Percutaneous Electrical Nerve Stimulation (PENS). PENS has been shown to have high efficacy in horses and humans alike, but requires frequent initial treatments. which are cumbersome to perform in animal patients. The novel therapy described here includes subcutaneous implantation of a two-lead pacemaker electrical "generator unit", with implantation of the leads into the left and right infra orbital canals to allow PENS-like neurostimulation as needed, without sedation or veterinary assistance.

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