Hope for headshakers? [H&H VIP]

  • Just eight months after buying her Polish warmblood gelding Theo, Zoe Chilcott discovered that the seven-year-old developed signs of headshaking, writes Veronica Roberts MRCVS (author of the featured study).

    “In October 2013 he suddenly started to headshake,” explains Zoe. “He was so frantic with shaking and rubbing his head that he became unsafe to lead on a headcollar, let alone ride. His future looked bleak.”

    Zoe’s local vet was aware of a trial I was running with colleagues at Langford Veterinary Services, using a revolutionary treatment aimed at relieving the effects of headshaking. After referral, Theo underwent three treatments and has remained in remission since February.

    “Theo is still a sensitive horse but no longer has any restrictions, and you would never guess he had been diagnosed as a headshaker,” says Zoe. “The treatment has given him a future.”

    Most of us know of at least one headshaker. This distressing condition currently carries a poor prognosis, with many horses becoming unrideable due to frequent and uncontrollable vertical headshaking, often accompanied by signs of nasal irritation such as snorting and nose-rubbing.

    Traditional treatment is often ineffective. Yet this new research, to appear in the Equine Veterinary Journal, indicates that in certain cases the condition can be brought under control.

    Many horses displaying classic headshaking signs are suffering facial pain from a neuropathy (nerve disease) of the trigeminal nerve, the main sensory nerve to the face.

    Further studies are needed to find out how many horses suffer from trigeminal-mediated headshaking, but it is thought that 1-2% of the UK equine population (between 10,000 and 20,000 horses) are affected.

    Horses usually develop the condition somewhere between the ages of five and 12, and it may be a little more common in geldings. Onset is more likely to be sudden, as in Theo’s case. Owners typically report that the horse reacted as if a bee had flown up his nose.

    Headshaking can occur at rest but is usually worse with exercise and is rarely seen in a horse turned out in a field. About a third of horses are affected only during spring and summer months.

    The cause of headshaking is not clearly understood. All we know is that the trigeminal nerve is sensitised and therefore “fires” at a lower than normal threshold.

    Diagnosis and treatment

    My starting point for diagnosis is to listen to the horse’s history before performing a thorough clinical examination.

    Establishing whether the headshaking is occurring due to facial pain can be achieved with nerve blocks, in exactly the same way that an orthopaedic clinician uses nerve blocks to locate the source of lameness.

    I observe the horse headshaking, usually at exercise, then inject local anaesthetic around the trigeminal nerve by inserting a 10cm needle behind the horse’s eyes.

    The horse is then exercised in the same conditions. If the problem has resolved, this confirms that the headshaking is due to facial pain. If not, it does not necessarily rule this out as a cause.

    I then look for gross pathology (visual evidence) that could be responsible, by examining the mouth and eyes, performing endoscopy of the upper respiratory tract and guttural pouches and carrying out computed tomography (a CT scan) of the head.

    If we find no abnormalities, it is most likely that the horse is a trigeminal-mediated headshaker. Severity can be graded out of three. Unfortunately, the outlook is often poor.

    Using a nose-net improves signs in about a quarter of horses. This is thought to work by rubbing the nose and constantly stimulating the nerve — in a similar way that rubbing your elbow if you bang it makes it feel better. A nose-net is non-invasive, cheap and can be used in competition, so it is the first treatment to try.

    A number of medications used for human neuropathic pain can be tried and some horses will respond. These treatments have limited efficacy, however.

    Tablets can be expensive and are prohibited in competition.

    There is a surgical procedure to compress the nerve using platinum coils, which carries a long-term success rate of about 50%. In a study we performed, however, four out of 58 horses had to be euthanased due to side effects — so I wouldn’t recommend surgery unless euthanasia is the only other option.

    While myriad treatments and feed supplements can be found online, but for a true trigeminal-mediated headshaker these will largely be ineffectual.

    A management breakthrough?

    Working in collaboration with the neuroscience team at Bristol’s Southmead Hospital, we have been trying a treatment used in humans for neuropathic pain on horses with trigeminal-mediated headshaking.

    Called neuromodulation, the treatment involves percutaneous electrical nerve stimulation (PENS) therapy and aims to reset the threshold level of the nerve for firing to normal. A probe is placed directly over the nerve and stimulates it for a set time.

    In humans, the only reported side effects are a bruise at the site of probe insertion. If humans respond to treatment they can expect pain relief for a few hours, perhaps up to week, after the first treatment.

    Relief can last from a few days up to two weeks after the second treatment, and from two months to occasionally six months after the third.

    After three treatments, required treatment interval seems to remain the same.

    We have just published results from a clinical trial in seven horses with grade 2/3 or 3/3 headshaking. The procedure was safe and well-tolerated by all under standing sedation.

    Five horses responded well and returned to ridden work, with duration of remission after the third treatment being between 2½ months and still ongoing at 10 months in one horse.

    The procedure is still in its infancy, and is merely a management technique rather than a cure. However, early results in some cases have been good and the risk of adverse effects appears to be low, although there are always risks to performing procedures with horses under standing sedation.

    In the absence of an effective, safe and well-established cure for trigeminal-mediated headshaking, I am trying this as a first-line treatment where nose-nets have failed to work.

    Ref: Horse & Hound; 25 December 2014