South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
The Headshaking Horse: Investigation and Management
Zoë Gratwick*
Equine Medicine Resident
Faculty of Veterinary Science, Onderstepoort
Headshaking is a spontaneously occurring disorder in the horse. It predominantly involves the
horse repeatedly flicking its head and this can often be accompanied by rubbing of the face on the
ground and other objects, despite a lack of visible stimulus. The severity of head shaking can vary
from mild, intermittent signs, to severe continuous signs. These horses can be highly distressed
and sometimes dangerous.
Headshaking has been reported in many countries across the world. The observed prevalence is
approximately 1%, although this is inevitably an estimate. Geldings are reportedly over
represented (71.5% of cases). Age of onset is variable, with reports of horses developing the
condition from between four and thirty years of age. Many breeds are affected and the condition is
observed across the disciplines.
Headshaking can be caused by a variety of different diseases, although an underlying cause is only
identified in a small percentage of cases. This leaves a large percentage of cases considered to be
“idiopathic.” It is essential that in order for a case to be considered idiopathic, a thorough
investigation for underlying, detectable pathology has been conducted. Conditions known to have
caused head shaking include: vasomotor rhinitis, allergic rhinitis, guttural pouch mycosis, fungal
sinusitis, dental disease, premaxillary bone cyst, temporohyoid osteopathy, floating melanotic iris
cysts, granula iridica cysts, ear mite infection, otitis interna, media and externa, cervical
osteoarthritis, cervical fracture, ill-fitting tack and behavioural abnormalities.
Prior to any further examination one should personally observe the head shaking behaviour,
whether by use of a pre-recorded video or by direct observation. Prior to the initiation of an
investigation, one should confirm that the behaviour is indeed headshaking behaviour. Also, it is
helpful to be able to judge the severity and nature of symptoms fo r one‟s self. The horse should
be observed ridden with both the usual rider and tack. It should also it should be seen without
them. In addition to a basic clinical examination, oral, ophthalmic, aural and neurological
examinations should always be conducted. Upper airway endoscopy, including assessment of the
guttural pouches is essential to exclude upper airway pathology. Radiography of the head also
constitutes an important part of a headshaking assessment, as a number of potential underlying
diseases may go undetected without radiographic imaging.
The role of the trigeminal nerve in equine idiopathic head shaking was recently confirmed by the
implementation of electrodiagnostics. It was observed that the infraorbital nerve of horses
affected by head shaking had a lower activation threshold than the trigeminal nerve of control
horses. Beyond this, the underlying mechanism for equine idiopathic head shaking remains
unknown. Some similarities exist between Human Trigeminal Neuralgia (HTN) and headshaking
in horses. There are however, a number of notable differences between the two diseases. HTN in
humans is classified as primary (idiopathic) or secondary (of known cause). In secondary cases
HTN lesions are often primarily found in the brain stem, rather than the peripheral nerve. This has
recently been raised as a topic for further research in headshakers. HTN is frequently caused by
pressure from a blood vessel on the trigeminal nerve as it enters the brainstem. Multiple sclerosis
(MS) lesions and tumours have also been observed to lead to pressure on the nerve leading to
HTN. This can cause demyelination and subsequently a functional axonopathy, leading to the
interpretation of tactile stimulus as pain. A disease similar to MS has not been reported in
horses, however given the difficulty of diagnosing this disease in humans, it remains possible that
such a condition exists in the horse. Furthermore, vascular anomalies and tumours could
potentially lead to such signs in horses. Further diagnostics such as contrast magnetic resonance
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