Dr Veronica Roberts is an RCVS specialist in equine internal medicine and senior lecturer at the University of Bristol Vet School. She is world-leading in headshaking research. Here she tackles three issues related to head shaking.
Problem: A mare experiences hair loss on her face in spring and summer, can be snotty and is a seasonal headshaker. Could these things be connected? What medical management strategies could be tried?
Veronica says… I’m sorry to hear that, it certainly sounds difficult to manage. The first step is to see whether the headshaking and the hair loss and snotty nose are connected. There is a complex — and not yet understood — association between environment and trigeminal-mediated headshaking, but it isn’t a ‘normal’ allergy.
Work out the timeline
With the hair loss, work out whether the itch or the hair loss comes first.
Does she become itchy after the hair falls out, or is it coming out because she’s itching and rubbing? Is she rubbing due to discomfort from trigeminal-mediated headshaking triggers, or are they separate things? Does hair loss/itch start before or after her seasonal headshaking signs return? Working out these things will be helpful to your vet.
Could she be asthmatic?
When she has a snotty nose, have an endoscopy carried out and take a sample to see if she has asthma. These things can be connected. If she does, discuss treating it with steroids with your vet, if appropriate for her. This will allow you to see which of her problems resolve with this treatment, which might help you work out any association. Steroids are a more effective treatment for any allergy in horses than antihistamines, as their immune system works a bit differently to ours.
Not just naughtiness
Problem: A Thoroughbred mare is a headshaker, but only when ridden in three specific situations: when there are flies or midges; in light rain; when she isn’t in front of a group hack when trotting or cantering. Could she be getting cross, as there isn’t always a physical trigger, or is she experiencing something?
Veronica says… Trigeminal-mediated headshakers appear to be suffering neuropathic pain in response to stimulation of their trigeminal nerve, which is the main sensory nerve to the face. Horses with this condition have a trigeminal nerve that is about 10 times more sensitive than normal.
This seems to cause neuropathic pain — people who suffer from this describe as varying from pins and needles, bearable to unbearable burning, and bursts of electric shock-like pain. It is this pain and altered sensation that makes horses throw their heads.
The increased sensitivity means some horses will experience pain when exposed to anything that stimulates the nerve, such as flies or rain, and whether they are ridden or not. See if she does it on the lunge, or on a lead or long-reins if safe, or if it’s only when on a ride. Trigeminal-mediated headshaking becomes a more likely diagnosis if she does do it when exercised but not ridden, although not certain without further investigation.
Is anxiety a factor?
If she isn’t affected at rest by the presence of flies, then it doesn’t rule out either anxiety or trigeminal-mediated headshaking, as trigeminal-mediated headshakers are more likely to suffer pain at exercise than at rest. When she’s doing it behind the others, think about whether she is in the firing line for dust or particles kicked up by them, or even wind disturbance, which could stimulate the nerve, or whether this is just her way of expressing anxiety.
A serious syndrome
Problem: How extreme would headshaking need to be for a horse to be considered for PENS treatment?
Veronica says… EquiPENS™ is minimally invasive and low risk. It works through inserting a small electrode into the trigeminal nerve while the horse is under sedation, with the aim of returning the nerve to its ‘normal’ state and function. The RCVS published a study on its use in 168 horses (530 procedures) in the UK and Europe. It is suitable for any properly diagnosed trigeminal-mediated headshaker who either doesn’t respond at all or sufficiently to use of a nose net, or where a nose net isn’t suitable (they are not allowed for all competition types and levels).
PENS™ success statistics
We expect half of horses to go into remission (where they are able to perform ridden work at their previous level), but only 18% are cured. The others will need repeat procedures when they start headshaking again. The majority of these will go back into remission again and for longer, but there are a small number of horses which do cease to respond. Where horses do not respond to treatment, we have to consider their welfare and quality of life. Some horses only experience the pain at exercise and can be retired, but this isn’t always an option for the owner or even the horse. Others will be affected even at rest and, for them, they would be in pain even in retirement. This does mean that, sadly, some trigeminal-mediated headshakers do have to be euthanased.