Headshaking/Head Flicking/Trigeminal Mediated Headshaking
In Spring and Summer the number of cases of headshaking appears to increase, so if this a real increase or potential misdiagnosis? In this article, we are going to cover….
- What is headshaking
- What are the triggers
- What is the underlying cause
- What options are there for treatment and management
We also have two excellent webinars by veterinary surgeon Dr Kirstie Pickles, a recognised international expert on headshaking, on Trigeminal-Mediated Headshaking:
What is headshaking
What does headshaking look like? Generally, it’s quite sudden and violent and, to some extent, abnormal shaking of the head. It’s different to the action of horses, for example, to flies or to dental pain or resisting the bit. It’s usually a violent vertical shake or flick. And another feature would be that when horses are headshaking, they will do this for considerable periods of time and very frequently, sometimes even continuously. Horses may be affected at rest, but generally, a key feature is headshaking during exercise, so for a clinical investigation, a simple luging test is commonly used. Many horses are triggered by light, so sunny days often increase the frequency and severity of headshaking.
Headshaking was first described by Williams in 1897 as a “neurosis of the infraorbital nerve”. The infraorbital nerve is a branch of the trigeminal nerve. Headshaking is assumed to be neuropathic pain affecting the trigeminal nerve. People with trigeminal neuralgia describe sensations such as burning, itching, tingling and “electric shock-like” pain. This is consistent with the clinical signs seen in affected horses; rubbing the face, shaking the head and striking at the head with the forelegs. In the image below the trigeminal nerve is shown in red. The nerve actually originates further back in the brain but passes through internal bony channels in the head, emerging around half-way down the head. The trigeminal never has branches on both the left and right side of the head.
Many studies have tried to understand headshaking, but it’s far from fully understood. There are also many “treatments” for headshaking, but relatively few have been properly assessed. Furthermore, few have evidence of efficacy.
How common is headshaking?
A study in the UK found that within a single year, 4.6% of owners reported their horses headshaking. However, only around 30% of owners had contacted a vet, leading to the conclusion that medically significant headshaking affects around 2% of the UK horse population. Around 600,000 to 1,000,000 horses in the UK so potentially up to 20,000 horses in the UK may be affected. Headshaking is a distressing condition both for affected horse and their owners.
What are the signs of headshaking and possible causes/triggers?
Signs of headshaking, as already mentioned, consist of violent, usually vertical (up and down) jerks of the head. There may also be muzzle rubbing. Owners often describe headshaking affected horses as “zoned out”, looking into the distance or anxious. Many owners also report their horses headshake seasonally and some report that it becomes worse as they age, including a change to headshaking all year around. Many headshaking-affected horses are also reported by their owners to be worse in bright, sunny conditions, with a similar number reporting headshaking triggered by eating, with the third highest reported trigger being wind. Eating is of interest as the teeth are innervated by the trigeminal nerve. Other possible factors reported by owners include: rain, snow, sounds, pollen and flies. Finally, in this survey the investigators surveyed owners in the UK and USA and found very similar responses.
With respect to seasonality, around 60% have seasonal variation. Some horses may have very specific times each year when symptoms start. Another suggestion as to why headshaking may be seasonal is related to the change in grass growth. However, overall, headshaking is lowest in November through to February, starts to increase in March and peaks around May-July and then gradually reduces over July to November.
The typical age of onset for headshaking is around nine years, with geldings possibly around 2x more likely to develop headshaking, although other studies have not found this effect. With respect to breed, there is some data to suggest that Thoroughbred may be 3x more likely to be affected compared with other breeds.
Diagnosis of headshaking
Diagnosis of headshaking is usually based on excluding other possible causes, such as dental disease, fungal infections of the nose, sinusitis, etc. These horses may headshake, but if the underlying condition/disease is treated, the headshaking stops. In one study, 98% of headshaking cases had no evidence of pathology. Another interesting diagnostic procedure is local anaesthesia of the infraorbital/maxillary nerve, which can significantly improve headshaking symptoms.
In people following Chickenpox infection, the virus can lay dormant in the nerves for years and under stress, the virus may “reactivate” or recrudesce. In people, this often manifests as Shingles. The Chickenpox virus is known as varicella zoster herpesvirus and its common for those affected by Shingles to experience chronic trigeminal nerve pain in the face; this may often be referred to as neuralgia. Herpes viruses are common in horses, and almost all young horses are exposed to EHV-1 so it has been proposed that a similar situation to Shingles may be active in equine headshaking. However, a study by Aleman et al. in 2012 only found EHV-1 present in the trigeminal nerve ganglia in one headshaking case out of 11 controls and eight headshaking cases.
Treatments for headshaking
It’s previously been mentioned that many owners report and increase in the severity of headshaking in bright and sunny conditions. There is a genetic (inherited) condition in people where bright sunlight causes sneezing and a tickling sensation in the nasal mucosa – close to the trigeminal nerve.
There are many treatments available or proposed for headshaking, but there are few formal studies of efficacy. Most treatments are only available through a vet, but ones that don’t include:
- Nose nets (50-70% improvement)
- Face masks (50% improvement)
- Magnesium glycinate, citrate or aspartate – 10g once or twice a day (43% improvement)
- Chiropractic therapy (<10% improvement)
- Fly control (<10% improvement) (Find out more here)
In two trials, nose nets reduced symptoms of headshaking in 50% and 70% of horses, whereas a facemask/fly mask was found to reduce symptoms in 50% of horses, so these are definitely worth trying. It’s important to select a dark-coloured mesh and a mask/net with high UV blocking. Not all products on the market meet their claims.
Check out the research and work we have already completed on UV Masks this – click on the titles to see.
- Fly Mask Survey Results
- UV masks and goggles
- The results – UV horse mask testing
- Horse UV and fly mask fit review
Veterinary treatments for headshaking include:
- Cyproheptadine (70% improvement)
- Carbamazepine (88% improvement)
- Cyproheptadine + Carbamazepine (80-100% improvement)
- Antihistamines (33% improved)
- Fluphenazine (44% improvement)
- Corticosteroids (54% improvement in one trial but only 15% in another)
- Sodium cromoglycate eye drops (improvement in 3 horses)
- Melatonin (29% improvement in one trial and 47% in another)
- Acupuncture (24% improvement)
- Platinum coil implantation (50% improvement)
- Ivermectin (anecdotal, unknown)
- Electrical therapies
- PENS – percutaneous electrical nerve stimulation (50% improvement)*
- TENS – transcutaneous electrical nerve stimulation (unknown)
- Electroacupuncture (unknown)
*PENS is a recognised and commonly used treatment in people e.g. for Shingles related pain.
Recent research into headshaking
Part of the problem with headshaking is that it is usually highly variable and we still don’t really know what causes it. This is one reason why vets Dr Veronica Roberts from Bristol Vet School, Dr Kirstie Pickles from Nottingham Vet School and myself have been reaching ways to better quantify when and how badly horse are headshaking using sensors mounted on the horses head. This will help us better understand triggers and response to treatment and is supported by a grant from the Langford Trust https://langfordtrust.org/. The graph below shows two examples of head movement (acceleration) during lunging at trot for 5 min from a control horse without headshaking and a horse with headshaking. In the control horse the head motion is normal for trot and very consistent whereas we can see from the headshaking case that the recording is more variable and the peaks accelerations are much higher; these represent shakes or flicks! (Roberts, Pickles and Marlin, unpublished data).
What to do if you think your horse is headshaking
- Look at the video example. This shows a severe headshaker (click here).
- If your horse only begins to shake when exercising or exercising makes it worse, taking a video to show your vet is useful
- Try to keep a diary and note what you think may make your horse start headshaking or makes their headshaking worse.
- Contact your vet – they can make a diagnosis and rule out other possible conditions such as dental disease, which may mean your horse can make a complete recovery and is not a true headshaker as discussed here.
- There are a variety of treatments you can try for headshaking. There is generally no universal treatment that cures or improves all headshakers. According to Dr Kirstie Pickles, things worth trying are a UV-blocking fly mask/nose net, magnesium at 10-20g per day and PENS therapy.
Make sure you watch Kirstie’s excellent webinars to learn more!