Head Shaking

10th January 2018
What is headshaking?
 
  • The term headshaking simply refers to any shaking of the head – up and down or side to side or round and round (rotational).
  • Some horses show signs of headshaking all the time and some are seasonal or situation dependent.
  • Signs that can accompany the headshaking include snorting, lip twitching, nostril clamping, rubbing the nostrils on the floor or front legs and even striking out at the nose and face. These signs are usually only seen with trigeminally mediated headshaking (see below).

 

What causes headshaking?
  • Headshaking can be caused by any number of problems, including dental disease, sinus pain, bit problems, back pain, lameness, a naughty horse and rider problems. A small number of horses have a condition called trigeminally mediated headshaking and these can be thought of as the true headshakers.
  • Trigeminally mediated headshaking refers to an abnormality of the trigeminal nerve called trigeminal neuralgia. This condition has long been suspected to occur in horses, however it has only recently been proven to be present in headshaking horses.
  • The trigeminal nerve is the main nerve that transmits sensation/stimuli from the head to the central nervous system. The neuralgia causes affected horses to receive sudden intense pain signals from either no stimulus or something that is normally not a problem (such as wind up the nose) – essentially a phantom pain they can do nothing about. People with trigeminal neuralgia report it as varying from numbness to excrutiating pain and this probably explains the sudden, jerky response of flicking the head up (like they have had an electric shock) and also the rubbing/snorting etc that some horses show.
  • The specific cause of trigeminal neuralgia in horses is unfortunately still unknown. In humans it can be related to herpes viruses, however studies do not support this in the horse.

 

How is headshaking investigated?

 

  • Investigation of a horse with suspected headshaking involves trying to rule out all possible causes other than trigeminal neuralgia. This involves a full clinical exam with ridden work if necessary, dental exam, neurological exam, endoscopy of the upper airways and x-rays of the head. If the tests are all normal then trigeminal neuralgia is considered the most likely cause of the headshaking. A nerve block is also available to support this diagnosis, but it is far from a perfect test.

 

 

 

How is headshaking treated?

 

  • If any abnormalities are found during the initial investigations then these are treated as required.
  • Where trigeminal neuralgia is suspected then treatment is difficult. There are many different treatment methods for people with neuropathic pain and the success varies greatly from person to person for all methods. In many cases the condition cannot be treated. In horses, the following can be attempted (always bearing in mind that in some horses the condition is seasonal so many disappear and then reappear):
  1. Nose-nets. It is unclear exactly why nose-nets work for some horses and not for others, but they are always worth trying. The most likely explanation involves the complicated gate-control theory of pain, which can be simplified as ‘why rubbing your arm after hitting it makes you feel better’ – the constant presence of the net contacting the muzzle acting as the rubbing.
 
  1. Medications – drug trials of corticosteroids, non-steroidal anti-inflammatories (Bute), antihistamines and neuropathic painkillers can be carried out. Unfortunately the response is usually very poor and even if there is an improvement, horses can usually not compete on any of the medications. In fact, when horses improve with painkillers of any kind it is probably the case that the cause of the headshaking is not trigeminal neuralgia, but actually a ‘normal’ cause of pain that could not be detected during investigation and responds to the drugs.
 
  1. Coil surgery – this works by destroying the trigeminal nerve. It is rarely recommended now as the side effects can be severe and the success rate is very low.
 
  1. Percutaneous Electrical Nerve Stimulation (PENS) therapy

 

What is PENS therapy?

 

  • PENS therapy involves applying a controlled electrical stimulation to a specific branch of the trigeminal nerve. The stimulation pattern is designed to reduce the sensitivity of the nerve and stop the abnormal painful stimuli from reaching the brain. PENS is the only treatment that targets the abnormal nerve directly and it is therefore considered the best treatment currently available.
  • PENS therapy is minimally invasive and, other than the sedatives and small amount of local anesthetic required during the procedure, drug free. There are no significant side effects and people undergoing treatment report that the sensation is actually quite pleasant. The procedure is carried out in stocks and takes around 2 hours. Horses can be ridden again the following day.
  • There is very little hard data available on which to give advice regarding the success rate of PENS in horses, but anecdotally around 1/3 of cases stop headshaking for a period of time after the treatment, 1/3 improve and 1/3 show no change at all.
  • In almost all cases the improvement is transient only and repeated treatments are required.
  • Three initial therapy sessions are always given, with repeated treatments added as required. These should be given as soon as headshaking worsens again.

 

Please contact Matthew at the Baschurch clinic to further discuss the investigation and treatment of headshaking further – 01939 260251.