All Shook up - Headshaking Syndrome. Hoofbeats

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ne of the most distressing, frustrating conditions a horse can suffer from, headshaking is aptly named as, not only does it relate to the behaviour shown by afflicted equines, but also to what the treating veterinarian, owner and rider usually end up doing - literally shaking their collective heads in exasperation!

Not to be confused with ‘head nodding’ - the repetitive ‘bobbing’ movement seen in some horses in anticipation of their feed arriving or, when ridden, indicating the presence of lameness - headshaking is characterised by violent and sudden movements of the head, thought to be in response to some form of irritation to the face. Just what these irritating factors are, what causes them to be active at some times and not others and why they affect some horses severely and

others quite mildly, remain some of the perplexing questions still to be answered.

SYNDROME OR SOMETHING ELSE? From the outset, it’s important to establish that there’s really two categories of ‘headshakers’ - those suffering from what is known as headshaking syndrome and those affected by one or more of a myriad of other influences. Due to the enormity of the subject and the need to treat these two types of headshaking separately, it has been decided to divide this article into two parts. The first, in this issue, deals with the specific condition of headshaking syndrome. In a future issue, other common health and training factors that can contribute to headshaking - such as dental problems, allergies, respiratory/throat/ ear diseases, gear fit and behavioural factors will be explored.

Continued

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All Shook Up continued...

Headshaking Syndrome, a well-recognised, relatively common problem that seems to occur more frequently in geldings, most often affects mature horses from around the age of eight years, although it can also be seen in any sex or breed and at any time of life. Typically, the horse will exhibit at least two, if not all three, of the following; ‘flipping’ of the head in such a way as to send the muzzle upwards, ‘sneeze-like’ behaviour indicative of an insect either stinging or flying up the nose and rubbing often quite violently - of the nose against the legs, ground or inanimate objects.

Specifically, the tossing motion of the head is often very similar to what’s seen when a horse touches its muzzle to an electric fence, its look of surprised indignation also being much the same. The difference is, however, that the zap from the fence can at least be readily identified as what prompted the toss of the head whereas, in the case of the horse with headshaking syndrome, a concrete physical reason is much harder to find.

WHETHER IT’S THE WEATHER Of interest is that many cases of headshaking syndrome appear to have some relationship to seasonal weather conditions - this being either the onset or a worsening of the symptoms coinciding with the beginning of spring. In fact, research findings have indicated approximately 60% of horses exhibit their ‘headshake’ significantly more on sunny days compared to those that are rainy and/or windy. At first, scientists wondered if the connection they were seeing between warm weather and the headshaking phenomena pointed directly to allergies commonly associated with spring and summer - such as hayfever - as the underlying cause. This theory, however, is now regarded as unlikely, as there also seems to be other, totally different factors having an influence.

Changes in environmental light intensity, for example - such as those occuring naturally when winter turns to spring - are something many owners of headshakers observe as having a magnifying effect on rubbing, tossing and ‘sneezing’ behaviour. Research has also documented cases where a horse may become quite disturbed and frantically begin tossing its head when brought out from a relatively dark environment - such as a stable or indoor arena - but calms down if taken back inside or its head is covered.

Some owners report having to restrict their handling of light-sensitive headshakers mainly to periods when the light intensity is at its lowest or even after darkness has fallen. Obviously, this poses less of a problem in winter but is hardly practical for the warmer times of the year, when most riders want to be ‘out and about’ on their horse competing and enjoying themselves!

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brain trigeminal nerve ophthalmic nerve maxillary nerve mandibular nerve

The trigeminal nerves cover most of the face and nostrils and it is these nerves that create an electric shock-like sensation in affected horses in response to wind, sunlight and other normal occurrences.

Left: Headshaking is characterised by violent and sudden movements of the head, thought to be in response to some form of irritation to the face.

A RAW NERVE It’s only been in fairly recent times that the intensity of a light source, in itself, has been found to be not the direct cause of headshaking behaviour, but instead a possible factor in causing irritation to one of the main nerves in a horse’s face. This nerve, known as the trigeminal, is one of twelve major ones passing through the head - it’s role being to control chewing movements and give feeling to some parts of the face.

Irritation of the trigeminal nerve, by a number of means, can produce severe ‘electric-type’, shooting pain, tingling and itching in the face. Researchers working on the equine headshaking puzzle have long been aware of this scenario as it also affects people (known as trigeminal neuralgia), so it was considered to be a likely piece of the whole clinical picture. However, it wasn’t until the mid 1990’s that a veterinarian John Madigan - read about ‘photic’ (lighttriggered) sneezes in humans, realised they were caused by irritation of the trigeminal nerve and wondered if the same could be happening to horses.

To test his theory that equine headshaking syndrome could be started or worsened in the same manner, Dr John Madigan then carried out trials where blocks of the

trigeminal nerve were performed just behind the eye and was successful in halting the symptoms shown by many of his equine patients. Suddenly, there was a feeling of optimism amongst those working to solve the mysteries of headshaking in different parts of the world and other research has since backed up his findings, with some horses showing up to 90 or 100% improvement following a trigeminal nerve block. Sometimes this procedure is combined with medication (usually carbamazapine), which seems to further boost the success rate in terms of the number of horses showing over 80% improvement.

It’s important to realise, however, that light isn’t always the ‘trigger factor’ for irritation of the trigeminal nerve, although it might seem that way from what’s been said so far.

Other possible irritants for individual horses are thought to be exercise, post-viral neuritis (usually after infection by the herpes virus), some sounds, some feed components, some smells, a high ambient temperature, sweating and raised body heat.

DAMPENING IRRITABILITY Finding out which irritating factors (there can be more than one) seem to be stimulating the nerve pain that, in turn, produces the headshaking response, calls for some dedicated detective work on the part of both the treating veterinarian and the

owner. As there are a number of treatment and management options that can be tried, this helps in narrowing down what is more likely to have a positive affect, rather than wasting time and money on every possible approach ‘just in case it helps’.

If one of the main stimulants for headshaking seems to be light intensity that is, the head tossing becomes worse on sunny days and reduces in a dark environment - it’s worth first trying some simple measures to reduce the irritating effect on the trigeminal nerve rather than resorting to a blocking procedure. A mask and/or goggles that act to reduce ultra-violet (UV) light by between 86-95% can be worn by the horse if it’s turned out during the day in spring and summer. Although these may look a little strange, the fact that a lightsensitive headshaker can virtually live a normal life with their assistance is a great relief to many owners - who, although they may still not be able to ride the horse to its full potential at times, prefer this to any other management options.

Another strategy that works on some lightsensitive horses, but not all, is what is known as tactile stimulation of the muzzle area, which can be achieved by something as simple as attaching a cotton fly veil (the old fashioned type with the ‘dangly bits’ of string hanging down) to a noseband, placing a stocking over the muzzle and lower part of the face or fitting a commerciallyavailable ‘nose net’. Observe what happens when the horse is wearing any of these both at rest and when under saddle and decide if it makes a difference to the frequency and severity of the headshaking behaviour. If it does, that’s a fairly clear indication of irritation of the trigeminal nerve being the underlying problem.

So how does this work? The same way as putting a finger under your nose sends nerve impulses to ‘block’ the feeling of an oncoming sneeze. Far from being an ‘old wives tale’, the ‘cloth under the nose’ phenomena was first related to equines way back in 1897 when it was apparently used with success on a headshaking carthorse in New York City!

A nose net or similar may also help if exercise seems to be one of the trigger factors for headshaking. - this being because it can have a ‘dampening’ effect on irritation of the trigeminal nerve caused by the dilation of blood vessels in the nose and sweating.

MEDICATION There are two drugs that some research has shown to have a positive influence on headshaking syndrome, these being cyproheptidine and carbamazepine. Both these treatment options aim to ‘calm the hyperactivity’ of the trigeminal nerve - that is, to make it less reactive to the factor it is being irritated by so it doesn’t ‘fire off’ a painful feeling as often or as strongly.

Cyproheptidine is thought to be especially

Top left and left: Attaching a cotton fly veil (with the ‘dangly bits’ of string) to a noseband or fitting a commercially-available ‘nose net’ can help a light sensitive head shaker live a normal life.

Above: Rubbing of the nose - quite often violently - against the legs, ground or objects, is one of the identifying symptoms of the head shaker.

Below: Some head shakers are light sensitive and will begin tossing their heads when taken outside from a relatively dark stable. Research has indicated these horses will calm down if taken back inside.

useful in the management of light-sensitive (photic) headshaking but sometimes it will be recommended to give a trial course of both drugs separately then together.

Improvements can be noticed within 24 hours of starting this medication if the correct diagnosis of trigeminal nerve involvement has been made.

Where there is a history of no headshaking in winter, melatonin may be suggested as a means to ‘trick’ the horse’s body into behaving the same way in the warmer seasons (when the days are longer and light more intense) as it does in the colder months. This involves placing the medication on a sugar cube and giving it to the horse between 5pm and 6pm, commencing at the end of spring. Although said to be effective in reducing headshaking in some cases, melatonin may also affect a mare’s reproductive function and the shedding of a winter coat.

Another option, especially if a case of headshaking syndrome doesn’t seem to have a light-intensity component, is to investigate via blood tests the possibility of the herpes

virus being present - as this can be a cause of facial nerve irritation. If detected, a course of immune stimulants is worth trying. Some research has indicated that combining this drug therapy with chiropractic treatment can enhance its success.

THE LAST RESORT So why, might beg the question, instead of trying all the above management strategies, don’t veterinarians and horse owners go straight to the option of surgery to block the nerve being irritated - especially when the research indications are of this being effective in treating many cases of headshaking syndrome?

Well, it would be wonderful if things were that simple but, unfortunately, the equine trigeminal nerve is not an easy one for surgeons to gain access to. Due to its location in the face, at this stage only a small portion of it can be blocked, which means that, although this might see a resolution of symptoms for a short time, there is a high possibility of them returning in the future.

This scenario is what has lead to this type of surgery really being the last resort as, not surprisingly, the risks and costs associated with the multiple procedures likely to be required for long-term freedom from the syndrome are beyond the means of most horse owners. Still, researchers are hopeful of one day being able to develop a way of blocking the trigeminal nerve from its starting point deep inside the brain - this having been how the human equivalent of trigeminal neuralgia is successfully treated.

If none of the classic signs of headshaking syndrome seem to apply to your horse, yet head tossing is something that does cause problems either from time to time or on a daily basis, there may be some good news.

The cause of the behaviour may well be a relatively simple one and be considerably easier to manage than what’s just been discussed! This will be the subject of the second part of this article.

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hilst headshaking syndrome in horses was first reported over 100 years ago, there is still no consensus amongst researchers as to the pathology of the disease (i.e. the cause remains unknown). However, it is now widely accepted that headshaking is caused by pain in one of the nerves in the face.

In fact, headshaking in equines has been likened to facial pain syndromes in humans – most notably Trigeminal Neuralgia (pain in the trigeminal nerve), a condition so painful it’s often referred to as the ‘suicide syndrome’. Horses are thought to experience tingling/itching/burning sensations - often intermittently, which can make identifying the trigger even more difficult - as a result of an abnormality in the function of this nerve (rather than a nerve that is physically damaged). The trigger that elicits headshaking is thought to differ between individual horses, and the same is true regarding the success of treatments.

The condition is a distressing and frustrating one, and in severe cases may result in euthanasia due to welfare issues, which is why a recently published study from researchers in the UK, identifying a surgical procedure that resolved headshaking in almost 50% of horses, is receiving much interest from horse communities worldwide.

Researchers from the University of Bristol’s School of Veterinary Sciences assessed the success rate (long term) of a new surgical procedure known as ‘caudal compression of the infraorbital nerve’, during which platinum coils were placed into the infraorbital canal in order to relieve pain. The study followed up on previous cases that had undergone the procedure at three hospitals between 2004

and 2011, as well modifying the procedure to use on new, additional cases. Though some horses required a repeat procedure, and four surgically treated horses exhibited postoperative nose rubbing, which did not resolve and resulted in euthanasia, the overall success rate (from the most recent surgery) was 49% - similar to that seen in the surgical treatment of trigeminal neuralgia in humans. The findings of the study offer much needed hope for those who have horses that suffer from headshaking syndrome.

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leading expert in the field of Equine CranioSacral therapy - Maureen Rogers from the USA has noted that equine headshaking comes in all different shapes, sizes and packages and plagues horses worldwide! The horses she treats around the world have one common factor, regardless of age, breed, diet, environment, discipline or training, and that is the fact they have all suffered head compression. The symptoms of headshaking vary from horse to horse with some symptoms more severe than others, and some horses becoming unrideable due to the severity and danger.

Once the horse owner has had the vet diagnose their horse, the teeth checked as a possible contributing factor and infections and/or other causes are ruled out, it’s important to take into consideration head compression and injury. Maureen is a pioneer in the field of equine craniosacral therapy and has treated horses that suffer from headshaking worldwide with successful results. Many clients she has worked with have exhausted both allopathic (western or evidence based) vet medicine options and others. After a head compression the pressures exerted on the horse’s head are not normal, nor is the amount of head injury, which many times is discounted and affect bone structure, nerve function, etc.

Craniosacral therapy is a gentle, hands-on method that involves the application of light pressure to specific points that directly address common problems in performance horses. Therapists work directly with soft tissue and apply craniosacral techniques that enhance healthy movement and release muscular and skeletal restrictions throughout the body. These methods can be learned and applied by horse owners and specialists as a way of maintaining the overall health and well-being of the horses between competitions. www.equinecraniosacral.com April/May 2013 - Page 19