Headshaking - a symptom of discomfort

Headshaking is one of the most frustrating equine symptoms, and one of the main reasons why I started to perform acupuncture. Most of the horse owners with horses suffering with these symptoms generally associate the headshaking to be due to trigeminal nerve pain.

The trigeminal nerve is a cranial nerve. This means that it emerges directly from the brain stem and has a role in both sensation and getting muscles in the face to move. This nerve has 3 main branches which go to the:

1. Eyes - ophthalmic branch.

2. Muscles around the lips and nostrils - maxillary branch.

3. Jaw - mandibular branch.

Increased sensation of the nerve due to certain triggers causes head tossing due to the sudden discomfort. This is a sign of pain.

The reason why I call headshaking a symptom, and not a condition, is because the head tossing is the outward expression of something else affecting the body.

What does a 'symptom’ mean?

When you have a runny nose, it’s not because ‘you have a runny nose’, but rather because you have a cold or allergy (amongst other causes). Your body therefore produces extra mucous to try to get rid of what is causing the cold/ allergy and to protect from further damage. A runny nose is therefore a symptom of a cold or allergy.

However, people also get a runny nose when they cry, because tears drain into the nose, this makes the mucus more watery, hence the runny nose accompanies the water works.

Headshaking is a symptom of a number of different conditions, which makes diagnosing the root cause of it extremely important before treating it.

What can headshaking be a symptom of?

1. Trigeminal nerve pain.

2. Musculoskeletal disease, including the temporomandibular (jaw) joint and poll.

3. Dental disease.

4. Ill fitting tack, including bridle.

5. Ophthalmic (eye) disease.

6. Neck threadworms.

Unfortunately, trigeminal nerve pain can not be accurately ruled out. There is no gold-standard test with 100% accuracy which can determine whether your horse is a headshaker due to trigeminal nerve pain.

But if it’s nerve pain, can’t you just block it?

No. Nerve blocks are unreliable (1) and may result in a number of side effects (2).

Trigeminal nerve pain is therefore a condition of exclusion, meaning that you must rule out all the other causes before accepting that your horse suffers from this condition.

All of the other conditions causing headshaking can be separately assessed, and one by one, ruled out, before accepting that your horse should be treated for trigeminal nerve pain.

This can be extremely frustrating - as implied in the name, trigeminal nerve pain is just that, painful. Nobody wants their horse to suffer and if it takes a long time to actually finally decide that your horse is a head shaker, then they would have suffered for an extended period of time.

Which horses are most likely to suffer from trigeminal nerve pain?

Headshaking is primarily a disease affecting adult gelded horses, with an average age of 9 years (3). The majority of headshakers show seasonal signs of uncontrollable, violent flicks (3), particularly in spring and early summer. This may also be due to the presence of ultraviolet (UV) rays (4). This does not mean that mares and older horses cannot get it, or that it cannot start at another time of the year.

The trigeminal nerve in the horses that have this horrible disease is triggered/ excited more easily (5), and this leads to pain (6). As 5% of horses that have started headshaking due to this disease suddenly stop for more than a year (7), it gives hope that this ‘easy triggering’ may be changed by itself.

So it’s mainly caused by pollen and UV - why?

In the initial part of the blog, I discussed the trigeminal nerve, and how it has sensory functions and how it provides branches to the lips, nose and eyes. I later wrote about how the trigeminal nerve becomes more sensitive in horses with trigeminal nerve disease.

It therefore makes sense that in these super sensitive horses, that increased exposure to pollen and UV increases discomfort.

So surely, management will help?

Yes and no. You can’t stop exposure to UV (sunlight) and you can decrease exposure to certain pollens only to a certain extent. In my experience, pain relief in the form of ‘Bute’ or ‘Danilon’ does not really help with trigeminal nerve pain.

Management is therefore key in any case of trigeminal mediated headshaking. 75% of owners report an improvement of clinical signs when the horse is made to wear a nose net (8). I have not been able to find specific studies about UV masks and decreasing signs of headshaking, however, decreasing UV penetration should help to decrease the sensitivity and therefore discomfort. There is a lot more research into the benefits of UV protection in decreasing ophthalmic (eye) disease in people.

One of the horses I was asked to look at headshook when being led out to hacking trails through passageways with ivy. Disappointingly, the horse’s discomfort did not improve with treatment. However, as the headshaking was so obviously happening whilst being led out through this passageway which could not be avoided, the owner made the decision to change yards, resulting in the headshaking stopping.

OK, so you can’t really diagnose trigeminal nerve pain, how do you rule out everything else?

This is the most frequent question which I am asked in regards to headshaking. Before I accept to see a horse for headshaking, I always try to ensure that the horse has ticked off the following checklist procedures:

1. Routine dental inspection with a qualified equine dental technician or with a vet with a keen interest in dentistry.

2. Tack assessed by a qualified saddler, this includes the bridle as well - I have assessed horses that only showed signs of headshaking when in their bridle, but not when in a rope halter. This may indicate that there is too much pressure at the jaw joint (the TMJ), at the poll or in front of the facial crest (this is where the maxillary branch of the trigeminal nerve emerges from the skull).

3. Following a strict worming program - I have personally never seen a case of neck threadworm in the UK, however, I know other vets who have.

4. No ongoing, untreated musculoskeletal disease, especially if this is new - I have seen this in headshakers with previously undetected front foot pain - as the horses try to pull weight away from their front feet, they flick their head up, as if they were headshaking. I do think that this may be one way of exhibiting discomfort and they are actually grimacing. I carry out a full musculoskeletal assessment on each initial consult.

Once I am satisfied with the checklist, and again, it is extremely important that the owner understands why they need to be so rigorous with these checks, I proceed to an assessment.

During an initial assessment, I do not directly treat trigeminal nerve pain. This assessment is based on:

• Fully understanding the history associated with the horse.

  • This includes a discussion about whether the horse has regular nose bleeds from one particular nostril, past dental disease, periods of having a respiratory noise during ridden work etc.

• Fully understanding the history associated with headshaking - when did it start, what sets it off, what has the owner tried. Does it happen when the horse's head is up or down?

• Ensuring that the owner completely understands how headshaking is just a symptom of trigeminal nerve pain.

• Performing a dynamic assessment - seeing the horse move under saddle and/or in hand. I check whether:

  • Are there any signs of lameness?

  • Does the horse only headshake on one rein?

  • Only under saddle?

  • Only in its bridle?

  • Does it depend on the position of the horse?

• The findings are then discussed with the owner, before treatment with chiropractic, myofascial release and acupuncture.

• A diary with a scoring system is put into place, together with a plan which aims to reduce specific causes of headshaking, one by one.

Depending on the clinical findings from this initial assessment, further diagnostic imaging is discussed in the form of an endoscope (camera into both nostrils to assess symmetry) and a head and neck CT, to ensure that no other disease which may cause headshaking are present. This includes dental, sinus and hyoid disease, nuchal bursitis (basically, this means significant poll pain), arthritis in the jaw, poll or neck etc. Although a CT is more expensive than a few X-Rays, it is significantly more diagnostic than X-rays. If I had a headshaking horse, I would elect for a CT +/- an endoscope.

What does the diary look like?

The diary is a slight adaptation from that set out in a 2017 study (9) which also shows the effectiveness of electro-acupuncture in treating trigeminal nerve pain.

• At rest;

  • 0: No signs.

  • 1: Occasional, mild signs.

  • 2: Moderate signs.

  • 3: Severe signs.

• At exercise;

  • 0: No signs.

  • 1: Riding still enjoyable for owner and horse, however exhibits mild signs.

  • 2: Riding not enjoyable, exhibits moderate signs.

  • 3: Unrideable.

So I ask the owners to track a few different things:

1. Date.

2. Exercise the horse has done.

3. UV rating.

4. Humidity rating.

5. Temperature.

6. Pollen score.

7. Grade at rest.

8. Grade during exercise.

Every few days, a change is made to the horse’s routine - this can be the introduction of a nose net, UV visor or administration of pain relief. This initial diary is short, to try to limit variation in the environment (pollen and weather), but also to try to prevent prolongation of pain.

What next?

If the horse is still headshaking despite management changes and ruling out all other possible causes of headshaking (including diagnostic imaging), a treatment plan is put into place.

A number of medical treatment options have been investigated, however they have limited success with a number of side effects (10). Sodium cromoglycate eye drops in 3 cases (11) and feed supplementation with magnesium, particularly in combination with boron (12), have been shown to be useful in reducing signs of headshaking in certain cases.

Percutaneous electrical nerve stimulation (PENS) is a safe procedure used for neuromodulation (changing response to stimulation) of the trigeminal nerve. This procedure resulted in only 53% of 168 horses showing significant improvement after initial treatment, with an average length of not headshaking of 9.5 weeks (13). This procedure can only be carried out at referral centers, and may be cost inhibitive.

Electro-acupuncture is another option (9), and although the initial study (only 6 horses) was small, 3 of them completely stopped headshaking. This is performed at a horse’s stable, and the initial treatment course consists of 3 treatments, 5 days apart. More cases are required to understand the long term effect of treatment and success rates. The success rate may be due to which part of the trigeminal nerve is being stimulated. This is the type of treatment which I carry out.

Conclusion

Headshaking is an extremely frustrating symptom, even more so due to the fact that trigeminal mediated nerve pain is so difficult to actually diagnose. A combination of management changes and treatment options may be required to control these signs of pain.

References

1. Mair, T. (1999). Assessment of bilateral infra-orbital nerve blockade and bilateral infra-orbital neurectomy in the investigation and treatment of idiopathic headshaking. Equine Veterinary Journal, 31(3), pp.262-264.

2. Newton, S., Knottenbelt, D. and Eldridge, P. (2000). Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases. Equine Veterinary Journal, 32(3), pp.208-216.

3. Madigan, J. and Bell, S. (2001). Owner survey of headshaking in horses. Journal of the American Veterinary Medical Association, 219(3), pp.334-337.

4. Madigan, J., Kortz, G., Murphy, C. and Rodger, L. (1995). Photic headshaking in the horse: 7 cases. Equine Veterinary Journal, 27(4), pp.306-311.

5. Aleman, M., Williams, D., Brosnan, R., Nieto, J., Pickles, K., Berger, J., LeCouteur, R., Holliday, T. and Madigan, J. (2013). Sensory Nerve Conduction and Somatosensory Evoked Potentials of the Trigeminal Nerve in Horses with Idiopathic Headshaking. Journal of Veterinary Internal Medicine, 27(6), pp.1571-1580.

6. Amir, R. and Devor, M. (2000). Functional cross-excitation between afferent A- and C-neurons in dorsal root ganglia. Neuroscience, 95(1), pp.189-195.

7. Madigan, J. and Bell, S. (2001). Owner survey of headshaking in horses. Journal of the American Veterinary Medical Association, 219(3), pp.334-337.

8. Mills, D. and Taylor, K. (2003). Field study of the efficacy of three types of nose net for the treatment of headshaking in horses. Veterinary Record, 152(2), pp.41-44.

9. Devereux, S. (2017). Electroacupuncture as an additional treatment for headshaking in six horses. Equine Veterinary Education, 31(3), pp.137-146.

10. Aleman, M. and Pickles, K. (2015). Headshaking. In: M. Furr and S. Reed, ed., Equine Neurology, 2nd ed. John Wiley & Sons, pp.130-138.

11. Stalin, C., Boydell, I. and Pike, R. (2008). Treatment of seasonal headshaking in three horses with sodium cromoglycate eye drops. Veterinary Record, 163(10), pp.305-306.

12. Sheldon, S., Aleman, M., Costa, L., Weich, K., Howey, Q. and Madigan, J. (2019). Effects of magnesium with or without boron on headshaking behavior in horses with trigeminal‐mediated headshaking. Journal of Veterinary Internal Medicine, 33(3), pp.1464-1472.

13. Roberts, V., Bailey, M. and Patel, N. (2019). The safety and efficacy of neuromodulation using percutaneous electrical nerve stimulation for the management of trigeminal‐mediated headshaking in 168 horses. Equine Veterinary Journal, 0, pp.1-6.