Contrary to popular belief, headshaking is not necessarily a seasonal problem. Most investigations into headshaking cases are disappointing because there’s often no useful diagnoses, so no therapy can be applied.
Many different factors are blamed, including bad behavior, flies and seasonal reactions to pollen. It is now recognized by veterinary professionals that there is no single cause – and therefore no simple cure.
There seems to be, however, a common denominator. At the UK’s Liverpool University researchers have been investigating an alternate hypothesis. Most headshaking horses exhibit signs of nasal and facial discomfort and will try to avoid air turbulence in the nasal cavity and on the face. This indicates that the condition might be related to the trigeminal nerve, which supplies most of the sensory functions on the head: the mouth, face, ears, eyes, sinuses and nasal cavities. There are similarities to trigeminal neuralgia in humans, known as the ‘suicide disease’ due to the excruciating facial pain it causes.
Is seasonality a trigger?
For many years it has been thought that headshaking more commonly presents in the spring and summer months. Indeed, many cases seem very seasonal, which leads us to associate it with human hay fever. But nasal biopsies suggest this is not the case and treatment with antihistamines and cortisone rarely help.
It seems more likely that the conditions/irritants responsible for headshaking merely trigger the problem, rather than cause it. Although a previous study by Liverpool University* identified some seasonality with the majority of signs first being seen in April, May and June, there was also evidence of an autumnal onset of the problem in September and other non-seasonal cases during the winter months (see below).
Evidence of non-seasonal cases therefore supports the theory that headshaking might be related to facial nerve pain.
How close are we to a cure?
Other than the obvious option of avoiding the trigger factors, there is no medication that is consistently effective so therapeutic options are sadly limited at present. Cutting or blocking the trigeminal nerve eradicates the symptoms immediately, but it’s a very stressful procedure that doesn’t necessarily resolve the condition permanently.
Some research is being carried out to investigate the use of platinum coils, designed to cause swelling inside the structures that carry the nerve (performed on ~40 horses at Liverpool). This has the effect of dulling down the nerve rather than blocking it fully, but the nature of the procedure is limited by the damage caused to the nerve on insertion. The procedure has had mixed success but results suggest it is a technique worth developing.
Laser ablation is another potential treatment, where the diseased parts of the nerve are identified and killed. However, the outcomes are a bit hit and miss in that when it doesn’t work it often causes other complications.
So what’s the prognosis?
Currently for genuine headshakers, the outlook is poor. Only approximately 10% of cases are resolved, and a few more improved, BUT even that is better than the zero prognosis that was present until recently. Researchers are still working hard to try & find solutions.
*Newton, S. A., Knottenbelt, D. C., & Eldridge, P. R. (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), 208-216.