As in any other field, physical examination of your horse is an essential part when trying to deal with a neurologic horse. For example, one of the most important things when a vet is evaluating your neurologic horse is to determine whether an infectious disease is causing the clinical signs. A simple way of doing this, although not always 100% reliable, is to measure the body temperature: if a fever is present (>38.5C) then an infectious/contagious disease is more likely. Infectious causes of neurologic disease in the UK are uncommon but the most prevalent is Equine Herpes Virus (EHV) that usually courses as a respiratory disease (nasal discharge, increased respiratory rate and effort and fever among others) but that can progress to a neurologic disease that presents as a weak horse that might be unable to stand, urinary incontinence, poor tail and anal tone and loss of appetite. Other neurological infectious diseases such as Equine Protozoal Myeloencephalitis (EPM), West Nile Virus, Rabies or Lyme’s disease are extremely rare in the UK although they should not be forgotten due to the recently emerging exotic diseases around the world.
When evaluating a possible neurologic horse, it is also important to perform a lameness exam at the same time. This should include a static and dynamic examination to determine if the deficits found on your horse are proprioceptive or due to a musculoskeletal disease. It is also important to note the demeanour of the animal or any behavioural issues that could indicate that you are dealing with a neurologic case.
The central and peripheral nerves will be evaluated by the vet. For example, a head tilt or difficulty to chew or swallow are common signs of a cranial nerve problem (central system) while muscle wastage or sweat in an area other than the face (where the facial nerve may be affected) might indicate a peripheral nerve damage (commonly radial, suprascapular, femoral and sciatic). Fairly prevalent diseases in the equine population such as stringhalt and shivers affect the peripheral nerves as well.
The most common clinical sign of a neurological disease is ataxia (impaired coordination) which might manifests as toe dragging, stumbling and hypermetric gait among others. In order to determine if these clinical signs are due to a neurologic disease or a musculoskeletal problem, your vet might perform the following tests:
· Tail pull. We will consider a positive test when there is no resistance of the horse when trying to pull his tail while walking or standing from either side.
· Picking up the feet and crossing the limbs. A horse without neurologic disease should be able to have their feet picked up without resistance and return their limbs to a ‘normal’ standing position after the limb has been crossed. A delayed on this reaction or the inability to return to the ‘normal’ position would indicate a proprioceptive deficit.
· Tight circles. Horses with normal proprioception are agile and cross their hind limbs when spinning around the examiner without stumbling, swinging, pivoting, hitting one leg with the other etc.
· Figure of ‘eight’. Again, horses with normal proprioception should have no problems (as the ones described above) when doing a figure of ‘8’.
· Hills. Some horses might demonstrate a more obvious proprioceptive deficit when walking up or down a hill.
· Changing the position of the head. Again, some horse might show more neurologic signs when their position of the head has changed. For example, walking a horse with the head up might highlight an otherwise subtle neurologic deficit.
· Backing up. Horses naturally back up in a two beat gait similar to a trot in reverse while a horse with a neurological disorder might be reluctant to back up, hyperflex or hyperextend the limbs or be unable to keep straightness.
Characteristic gaits can be seen in horses suffering from stringhalt and shivers mainly affecting the hind limbs.
Sleep deprivation is not that uncommon in horses and is characterised by a drowsy horse and sudden fall for no apparent reason.
The loss of deep-pain sensation is the last function lost in neurologic conditions, and it typically carries a grave prognosis.
After all these tests have been performed in your horse, a grade of neurological disease to record the severity of the clinical signs will be given as follows:
· Grade 0 – The horse appears normal.
· Grade 1 – The horse is inconsistently abnormal under special circumstances.
· Grade 2 – The horse is consistently abnormal under special circumstances.
· Grade 3 – The horse is abnormal all the time.
· Grade 4 – The horse is extremely ataxic and may fall.
· Grade 5 – The horse is down and unable to rise.
Following the physical and neurologic exam, different tests can be used to determine what is the cause for the clinical signs present. These include:
· Samples: nasal swabs, analysis of cerebrospinal fluid, bloods etc.
· Radiography and ultrasonography of the neck: These are useful tools to determine any pathology affecting the neck.
· Myelography: A contrast solution is injected into the subarachnoid space to highlight any abnormalities of the spinal cord.
· CT, Bone Scan and MRI: They are more advanced diagnostic techniques that are being used more recently and that might help to diagnose more complex cases.
Apart from the infectious diseases mentioned previously, there are three main non-infectious conditions that are commonly diagnosed in neurologic horses: Head Shacking Syndrome, Cervical Stenotic Myelopathy (CSM) and traumatic injury. Your vet will diagnose them with the tools mentioned above.
Tetanus is a serious neurologic disease in horses that causes death in 90% of the diagnosed cases. However, thanks to the routine vaccination, against this disease, provided to the equine population in the UK; it is a condition rarely diagnosed by vets in our country. Special attention should be taken in horses with wounds, particularly those puncture wounds affecting the hoof. The disease is characterised by a spastic paralysis (rigid horse). Aggressive and early therapy is essential when trying to deal with this disease. At Chiltern Equine Clinic, we strongly advise vaccinating all your horses against tetanus and giving tetanus antitoxin in a case of a wound if the horse is not up to date with the vaccination at the time of the injury.
Botulism is also rarely diagnosed in horses in the UK. However, similarly to tetanus, it is highly lethal in these animals and a prompt diagnosis and treatment are essential when trying to treat this disease. Contrarily to tetanus, this disease is characterised by a flaccid paralysis with horses commonly lying down and unable to get up as the disease progresses but without rigid limbs as when they are presented with tetanus. Botulism is usually caused by the ingestion of contaminated forage, particularly large round bales.
Once a diagnosis have been made, a surgical and or medical treatment can be initiated.
The use of supportive therapy is sometimes the only treatment for infectious neurologic cases. These include: intravenous fluids, the use of anti-inflammatory drugs and any other nursing care that the vets might consider depending on the case presentation and the aetiology of the disease.
A fairly recent novel treatment for ‘Head Shaking Syndrome’ is available. This consist on the use of percutaneous electrical nerve stimulation (PENS).
The treatment for CSM might be surgical or medical depending on the cause. While osteoarthritis of the cervical facet joints is commonly diagnosed in horses and treated with steroids or regenerative therapies with good success, ‘wobblers disease’ (a congenital disease that causes typically young horses to have different grades of neurological disease) often requires a surgical procedure to at least improve the clinical signs if they are severe enough.
Sleep deprivation might be manage with a change in the environment such as turning the horse out more often as horses are more confident to lay down in an open field than in the stable. Your horse might need anti-inflammatories if the cause for the sleep deprivation is pain such as old horses suffering from hock arthritis that is preventing them from laying down. Remember that the rapid eye movement (REM) sleep in horses only occur when the lay down and therefore, you need to make sure that a suitable environment is available for each horse in order to ensure that they can lay down and rest properly.
If you have a horse that you might thing is neurological, please do not hesitate to contact us.