Providing Relief

Currently, there’s no cure for ­trigeminal-mediated headshaking. Many researchers have drawn comparisons between these horses and humans with a similar condition called trigeminal neuralgia. For this reason scientists have tried applying therapies used to treat neuropathic pain in people to headshaking horses, with mixed or only short-term results, says Roberts.

Many of the available therapies and procedures aim to relieve the horse’s discomfort, first and foremost. These might include:

Medication

Veterinarians have prescribed a number of drugs in an attempt to control the nerve pain associated with headshaking, with mixed results.

“Successes tend to be short-term,” says Roberts. “Furthermore, the drugs are expensive, carry side effects of drowsiness, and are prohibited in competition.”

One of those is the oral antihistamine (and seratonin blocker) cyproheptadine, which has shown a response rate ranging from 48% to 70% in various studies. Aleman says about 60% of the headshakers they administer this drug to at UC Davis show improvement. Other oral antihistamines have produced positive responses in some horses, but at lower rates and in conjunction with drowsiness and side effects such as lethargy and colic.

Masks and Nets

In horses for which sunlight is a clear trigger, these products might provide relief. Your everyday fly mask, however, won’t work; the mask must be specially made with ultraviolet light protection. “It doesn’t completely stop it, but reduces (reactivity) to the point the horse can be rideable again,” says Aleman.

The same goes for devices such as nose nets that dangle from the horse’s bridle over his muzzle. Roberts attributes their occasional success to gate-control theory: Essentially, a nonpainful stimulus closes the “gates” to the painful one, changing that sensory input from something that hurts to something ­innocuous.

Dietary Changes

Recently scientists have been studying headshaking horses’ diets. Specifically, says Aleman, they are looking into the effects of feeding alfalfa, which has a higher magnesium content than grass hay. Magnesium can help balance the body’s pH level, which is important for nerve firing as well as calming.

“When we change the diet of these horses, we may actually decrease or slow down the headshaking,” Aleman says of her team’s early observations of diet changes. “When we go back to diets that are lower in magnesium, horses start shaking a little more.

“Can you imagine if by just changing the diet or providing something to change the pH, you can completely avoid (headshaking)?” she adds. “That’d be a major, major finding.”

Supplements

Researchers have studied or observed nutritional supplements’ effects on headshaking, as well. The hormone melatonin, for instance, might help reduce the seasonal headshaking of light-sensitive horses when administered daily. Basically, it tricks the horse’s internal seasonal clock into thinking it’s winter.

For the aforementioned reasons Aleman also recommends supplementing affected horses’ diets with oral magnesium daily. Based on the results of an owner survey she conducted in 2014, supplementing with both melatonin and magnesium yielded positive results in 55% of treated horses.

Aleman cautions owners to use products containing only magnesium, and not multiple other ingredients, and to have the veterinarian monitor horses’ blood magnesium levels to avoid overdose.

“We have six horses in our center (at UC Davis) that were donated because they were unrideable and completely unsafe that we have been able to manage with diet and magnesium daily,” she says. “It has not stopped the headshaking completely, but we can now do things with the horses without getting injured.”

Neuromodulation

Researchers have recently taken a page from human medicine and applied neuromodulation therapy to affected horses. Roberts says this safe and minimally invasive procedure involves using a probe to electrically stimulate the trigeminal nerve for a short period, with the goal of “resetting” its normal threshold level for firing.

As of August 2017 Roberts says her team has performed approximately 500 neuromodulation procedures on standing sedated horses with no significant adverse effects. She says about a quarter of these produced long-term success, a quarter short-term success, and the remaining half no response.

“Some horses have a promising start but then fail to respond to later treatments,” she says. “It is my early impression that where horses respond, but for insufficient time, length of remission may increase with repeated procedures. It is still very early days and we have a lot to learn and refine.”

Surgery

Veterinarians have not yet devised a surgical procedure that consistently corrects headshaking. Roberts, however, participated in the development of one in which surgeons implanted platinum coils into the infraorbital nerve in an attempt to interrupt nerve conduction.

“It carries a long-term approximate success rate of 50%, but there is a significant risk of severe side effects, which may require euthanasia, and about a quarter of cases relapse,” she warns. “We therefore only recommend this procedure where euthanasia is the only other option.”

Aleman says potential complications associated with this surgery include aggravating pain and neuromas (tumors arising from a nerve), and many horses require more surgery or euthanasia. “Currently, I am not recommending surgery for this specific condition for any horse,” she says.

Determining which treatment or combination of treatments works best for your horse is likely going to require some trial and error, as each individual responds differently.

“That’s what’s been so frustrating about this disorder,” says Aleman. “You talk to several people, and they are going to tell you, ‘Yes, that works,’ or ‘No, that didn’t work.’ But what worked for one horse might not work for another. It’s very ­variable.”

Take-Home Message

Trigeminal-mediated headshaking is clearly a multifactorial problem, meaning a number of components play a role; environment, diet, hormones (since it primarily affects geldings), and pH levels likely all have an effect on its severity. And when no combination of treatments seems to help, sometimes euthanasia is the most humane option.

“This is such a frustrating disorder,” says Aleman. “We hope one day we’ll be able to help these horses, because it’s terrifying for the owner and devastating to see these animals going through that.”