Headshaking Syndrome in Horses

Headshaking in horses can vary from a gentle bobbing—a horse trying to shake away flies or scratch an itch—to severe, where a horse is almost constantly shaking despite no obvious cause. 

The first is a normal horse behavior, but the second is likely abnormal and may indicate true headshaking syndrome, also known as trigeminal-mediated headshaking (TMHS).

What Is Headshaking Syndrome in Horses?

Headshaking syndrome is a condition in horses that is characterized by severe, frequent, uncontrollable bouts of a horse shaking their head when there is no obvious stimulus present.

This syndrome is known to be associated with pain in the trigeminal nerve, which is responsible for the horse’s facial senses. This nerve gathers sensory cues from many areas of the horse’s face including the nose, jaw, and eyes. 

Episodes of headshaking syndrome are sometimes observed worsening in bright sunlight or during intense exercise.

This condition is seen in about 1% of horses, across all breeds. It is typically first diagnosed in adult horses and geldings seem to be overrepresented.

Symptoms of Headshaking Syndrome in Horses

Headshaking can be a normal way for horses to express themselves or get rid of pests. So how do you know if your horse’s head shaking is something to be concerned about? 

True horse headshaking syndrome is characterized by severe symptoms that don’t resolve when the suspected cause goes away.

Symptoms of headshaking syndrome may include:

• Nodding up and down (more common) or shaking side to side (less common)

• Snorting

• Rubbing the face/nose on forelimbs

• Striking at or trying to scratch their face with their limbs or on objects

If you feel that your horse is showing any of these symptoms more than a normal horse would, talk to your veterinarian.

Causes of Headshaking Syndrome in Horses

This condition has been recognized in horses for decades, but only in recent years has an explanation for the behavior been identified. 

In horses with headshaking syndrome, the trigeminal nerve is hyperexcitable. This means that the nerve fires on its own without the need for an obvious stimulus, such as a pesky fly. This causes the horse to feel a sensation of stinging or burning frequently or constantly, so they try to resolve the issue by snorting and shaking their head. 

At this time, it is not fully understood why this hyperexcitability occurs, but there is believed to be a possible genetic component as it seems to be more common in some breeds.

How Veterinarians Diagnose Headshaking Syndrome in Horses

Diagnosis of headshaking syndrome can be incredibly frustrating for horse owners. Unfortunately, there is no specific test to easily identify if a horse’s trigeminal nerve is hyperexcitable. This means that most cases are diagnosed by ruling out all other possibilities.

Some other conditions that can cause severe headshaking may include:

• Dental disease

• Ear infections or parasites

• Behavioral issues

• Ill-fitting tack

• Eye pain

• Guttural pouch disease

• Neoplasia (cancer)

It is important to start with a thorough physical and oral exam with your veterinarian. Since some cases of headshaking happen very intermittently, it can be very helpful to take a video of your horse during an episode to show your veterinarian what is going on.

Try to pay close attention to any possible triggers, including light, diet, tack, type or intensity of work, and weather. 

If the basic physical exam is normal, additional diagnostics may include:

• Radiographs

• Endoscopic exam

• CT scan

• MRI

How Do You Treat Headshaking Syndrome in Horses?

Unfortunately, headshaking syndrome in horses is not curable. Many therapies, including various medications and surgeries, have been tried with mixed results but none have completely cured the condition.

The severity of headshaking syndrome varies widely. For horses that are mildly affected, the prognosis is good. Severely affected horses have a poorer prognosis due to the impact it can have on their quality of life.

Some therapies may include:

• Cyproheptadine: an antihistamine that may help decrease nerve hyperexcitability

• Carbamazepine: a neuromodulator believed to help with neuropathic pain

• Melatonin: It’s thought his can be helpful because of the light association, or as a free radical scavenger

• Magnesium and boron: supplementation of these minerals in the diet is a recent development that is showing some promise.  They are important in the pathway for activating nerves and may help to decrease inappropriate firing.

• Topical anesthetics: These are thought to possibly help with some of the pain associated with the nerve firing.

Make sure to consult with your veterinarian before trying any of these medications or supplements.

Recovery and Management of Headshaking Syndrome in Horses

True headshaking syndrome is not curable, so most treatments aim at getting symptoms to a manageable level.

There are several products that may help improve your horse’s symptoms:

• UV fly masks

• Tinted polo eye guards

• Nose nets

Some horses have also responded to targeted chiropractic and acupuncture therapy.