The Facts of Headshaking

Learn what we really know about headshaking, a complex, confusing, and often frustrating condition.
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When treating headshaking syndrome, forego the gimmicks. Treatment requires patience and a step-by-step approach, guided by your veterinarian’s advice.

Wilma is a sweet, sensitive, and generally well-behaved 14-year-old Quarter Horse mare. So when she started tossing her head, her owner turned to the Internet for advice. She was especially excited when she found a Web site offering a quick-fix for headshaking. When that didn’t work, she contacted an animal communicator. But poor Wilma just kept right on shaking her head.

Wilma’s owner finally called the vet. “Wilma flips her head up and down, snorts, and sometimes acts like an insect is flying up her nose,” she explained. “On occasion, she even strikes at her nose with her front leg.” With the help of her vet, Wilma’s owner found an explanation for her horse’s symptoms: they’re the classic signs of idiopathic headshaking syndrome.

In spite of years of research, idiopathic headshaking syndrome remains one of the most mysterious conditions that can impact your horse. As with any medical problem that’s confusing to diagnose and difficult to treat, a suspicion that your horse has headshaking syndrome is likely to generate all kinds of untested theories, questionable suggestions, and questionable treatment recommendations. Here I’ll answer five common questions about this condition, discuss treatment options, and describe a promising new treatment for the condition.

What does it look like?

The facts: The most common sign of this condition (reported in 89 percent of affected horses) is frequent, sometimes-violent shaking of the head in a vertical (up-and-down) direction. In fact, 88 percent of headshakers are described as “acting like an insect is flying up the nose,” while 75 percent rub their muzzles on objects such as their own front legs. Other, less common, signs include excessive snorting or striking at the nose and seeking shade in unusual ways, such as standing with their head inside a barrel or large bucket. About half the horses with this problem experience worse symptoms during exercise. If you’ve ever seen a textbook headshaker, you won’t forget it. And there’s a good chance you’ll recognize the symptoms if you ever see them again.

The hard part: To an untrained eye, every case of headshaking can look a little different. Possible causes include dental issues, ear problems, or simply bad behavior. Even normal, well-mannered horses shake their heads from time to time. To complicate matters, some headshakers exhibit symptoms more often during exercise; most (but not all) are seasonally affected; and some are worse in bright sunlight, while sunlight won’t affect others at all. These variables can make diagnosing the condition difficult.

Who’s affected?

The facts: Headshaking syndrome can impact any horse at any age, but the average age of onset is 9 years. Geldings are more commonly affected than mares. Thoroughbreds are the most commonly affected breed, followed by Quarter Horses and Warmbloods. The syndrome appears to be more common in overweight horses and has been known to start after a layup period.

The hard part: A specific cause has yet to be identified, making it impossible to predict whether your horse could become a headshaker or do anything to prevent it. Considering that a horse can start showing symptoms literally overnight, idiopathic headshaking can be the stuff of nightmares for a horse owner.

Guide to Recommended Treatments
The key to successfully managing your horse’s headshaking syndrome requires patience and a step-by-step approach. Experts agree it’s generally best to start with a single treatment and stick with it long enough to determine whether it’s really working. Keep a calendar or a journal to track your horse’s progress.

The most common treatments fall into three categories: physical, nutritional,
and medicinal.

Physical
Control light exposure. If your horse’s headshaking is triggered by daylight, keep him in during the day, and turn him out at night. Ride in an indoor arena, or outfit him in a UV-blocking mask to reduce light exposure.

Weight loss. If your horse is overweight, a weight-control program is a reasonable step to take. The incidence of headshaking is higher in obese horses.

Try a nose net. As many as 75 percent of owners have reported improvement with use of a nose net. This device dangles over your horse’s nostrils and muzzle to stimulate the nerve to send an “up” impulse, which then prevents the nerve from sending the “out” impulses that can lead to symptoms. Nose nets are most effective in horses where exercise is a trigger; they can be worn during work.

Supplements or Over-the-Counter Medications
Magnesium. This electrolyte can have a calming effect and may help reduce hypersensitivity of the trigeminal nerve. To be effective, you may have to give it at a higher-than-normal dose, so it can be dangerous. Consult with your veterinarian on dosage, as monitoring magnesium levels in the blood might be recommended.

Melatonin. Melatonin adjusts your horse’s internal clock and can be helpful if your horse is a seasonal headshaker with symptoms starting every spring. It should be administered every night at 5 p.m., year-round, to be most effective.

Antihistamines. Over-the-counter antihistamines such as Benadryl or Zyrtec are often suggested, but rarely effective for treating headshaking syndrome.

Prescription medications
Cyproheptadine. This antihistamine can also be used as an antidepressant in humans. How it helps with headshaking is unclear, but cyproheptadine reduces symptoms in as many as 70 percent of affected horses, making it one of the most commonly prescribed medications.

Carbamazepine. This anti-seizure medication is used to treat nerve pain in humans. Some experts report that it’s also effective in a large percentage of headshaking horses. It can be prescribed alone or in combination with cyproheptadine.

Dexamethasone. This corticosteroid is a commonly suggested treatment, yet studies have shown very limited effectiveness.

Why does it happen?

The facts: Hypersensitivity of the trigeminal nerve is at the root of headshaking. The trigeminal (or fifth cranial) nerve consists of three branches (the ophthalmic, maxillary, and mandibular) and is responsible for facial sensation, as well as some biting and chewing functions. Nerve pain is typically described as burning, tingling, or like an electric shock, and can be quite severe. When your horse experiences these sensations in the trigeminal nerve, he responds by exhibiting the symptoms of head-tossing, sneezing, or rubbing his muzzle against his leg or other objects. Chances are your horse is experiencing severe pain, similar to a syndrome called trigeminal neuralgia in people often described as the most painful condition known.

Recent studies have led researchers to conclude that there’s no structural abnormality underlying the hypersensitivity of the trigeminal nerve. Instead it’s believed to be a functional (physiologic) problem.

The hard part: Why does it happen? That remains a mystery. A wide variety of triggers have been investigated—ranging from sunlight and exercise to hormones or a latent herpesvirus infection. In fact, some experts consider a sensitivity to sunlight (referred to as photic-headshaking) to be a subset of the syndrome, as some horses exhibit signs only during summer months, and symptoms can be controlled by providing protection against bright daylight. Exercise appears to trigger approximately 50 percent of cases. Other proposed triggers such as hormones or herpes infections haven’t been supported by results of research.

We don’t know what causes headshaking syndrome, nor can we reliably identify potential triggers for the majority of horses.

How is it diagnosed?

The facts: If your horse shows classic symptoms, your vet will make a presumptive diagnosis based on what he or she sees. Unfortunately, there’s no definitive test to diagnose the condition. You must rule out other issues, which requires a number of tests to eliminate other possible causes of headshaking before landing on trigeminal nerve pain as a final answer.

Your vet’s first step should be a thorough physical exam, including a close look at your horse’s mouth, teeth, and eyes. Simple causes for headshaking such as a grass awn in a horse’s nose are rare, but possible and easy to solve.

Skull radiographs can rule out tooth problems or other bony abnormalities within the skull. Endoscopic examination of your horse’s nasal passage and upper airway can identify foreign objects or other abnormalities that could cause headshaking. A CT scan of your horse’s skull might be recommended to look for other unusual potential causes such as tumors that could impact the nerve.

The hard part: Because there’s no test that can diagnose headshaking syndrome associated with trigeminal nerve pain with certainty, there’s no way you’ll ever have a completely definitive diagnosis of the condition. A diagnosis depends on ruling out other possible causes for headshaking, recognizing typical symptoms, and in some cases, a response to treatment.

Hope on the Horizon
Researchers have recently determined that the trigeminal nerve pain experienced by horses with headshaking syndrome is due to a functional (versus structural) abnormality. This means treatments that are focused on modulating nerve function have a reasonable chance of being effective.

A recent study investigating the use of percutaneous electrical nerve stimulation (PENS) as a form of treatment has been promising. Six out of seven horses in the initial study showed significant improvement after treatment, and veterinarians using the treatment in practice are excited about its success.

This treatment technique, commonly used for treating neuropathic pain in humans, involves application of an electric current through small needles placed near the trigeminal nerve for a period of time. Most acupuncture practitioners have PENS units available and can apply the treatment, which is noninvasive, inexpensive, and easy to administer. Even better, after the initial treatment, PENS can be used repeatedly on an as-needed basis to help minimize discomfort and control signs for your headshaking horse. If headshaking can’t be cured, at least it might be controlled with this new therapy to elevate your horse's comfort.

Is it treatable?

The facts: There’s no universally effective treatment for headshaking syndrome. And there’s no cure. There are, however, a wide variety of treatment options, ranging from physical changes (e.g., avoiding triggers) to prescription medications that help control nerve pain. For a rundown of the most commonly recommended treatments, see “Guide to Recommended Treatments” on page 56.

The hard part: No single treatment is effective all the time. One treatment might help one horse but not make a difference for another. To make things even more complicated, headshaking can be intermittent, and symptoms often disappear for periods of time (sometimes even years), making it hard to tell when a treatment is really working. Finally, while treatments might provide some relief and reduce symptoms, the condition is rarely (if ever) cured. Trial and error is about the only way you’ll find a treatment that’ll help your horse. This can make you desperate and open the door for untested and unreliable “miracle cures” you must be cautious about using.

If you suspect your horse has headshaking syndrome, consult with your veterinarian for sound advice. He or she can guide you through the diagnostic steps and help you choose treatment options in an educated, conservative fashion with your horse’s best interests in mind.