The Neurological Examination of the Horse
Suzie's 6-year old Hanoverian gelding, Koenig, was not doing well this spring. She had great hopes for him as an Amateur-Owner jumper, and during his 5-year old training year, he had shown flashes of brilliance. He had the ability to turn on a dime and hand you back the change, and, was as quick as a cat on his feet. He seemed to look at a 4-foot oxer as below his dignity – surely he had soared at least 5 feet in the air. She gave him the winter off, as he had a series of hoof abscesses, but now that they were cleared up, she expected that Koenig would quickly return to his previous form. Suzie reflected that it had been hard to put her finger on the problem, but as time went by, Koenig's ability to clear relatively small 3-foot fences had deteriorated, and he sometimes stumbled when making a quick turn. She'd had three different opinions by three different veterinarians, and none of them seemed to be able to pinpoint the problem. One said that Koenig had a hock problem, one said that he was foot-sore because of the old abscesses, and one suspected, much to Suzie's dismay, a neurological problem.
Unfortunately, this is a relatively common scenario. Even experienced examiners may differ as to the cause of a horse's abnormal performance or gait. One reason is that many horses, which we suspect of having neurologic disease, may also be lame. The hard part is sorting out which is the most important problem. Moreover, neurologic disease often mimics the signs that we see and expect in many lamenesses. The foundation on which a diagnosis of neurologic disease rests is a thorough, methodical examination. It is important that all aspects of the horse's ability to function neurologically be examined – and understanding the rationale behind the examination will help you to understand your horse's diagnosis.
The Neurological Exam
As with any examination, the history is extremely important. Suzie brought Koenig to the nearest referral facility, a school of veterinary medicine, where they were greeted by a clinician and a senior student. They sat down at a round table, and the questions began:
Is Koenig a gelding?
Certain diseases, such as cervical vertebral instability (Cobbler's syndrome) affect males more than females.
What breed is Koenig?
Certain diseases, such as cerebellar abiotrophy, are breed-specific.
How old is Koenig?
Certain diseases, such as degenerative myeloencephalopathy, are more likely to be seen in young horses.
How long has the problem been going on?
This may help to determine if the problem is something the horse was born with, or if it was acquired over time.
Have any other horses in the barn shown similar signs?
This may help to determine if there is an infectious or toxic cause.
What do you use Koenig for?
If the horse is in work, it is likely that the problem was noticed right away. If the horse has been out at pasture, it will be harder in many cases to pinpoint when the problem started.
The goal of the examination is to determine where the neurological problem is located. During the physical examination, a series of tests are performed to evaluate methodically whether various areas of the nervous system are affected. Once we know where the defect resides, we can have a much better chance to figure out the disease process that is causing the defect.
The examination began with them watching Koenig come off the trailer. This can be a useful part of the neurological examination, as it requires a fair bit of coordination for a horse to back down a ramp.
Dr. Smith, the clinician, asked the student, Do you see any obvious abnormalities – for example, is Koenig wobbly, or is he standing with his legs in unnatural positions?
The student, Becca, watched carefully, and then answered He seems fairly normal to me at this point. I don't see any obviously abnormal behavior or gait.
Good, said Dr. Smith. I agree with you. That helps us to grade the level of neurological disease that he may have. A normal horse – grade 0 – has no abnormalities. A horse that has grade 1 disease is usually only determined to be abnormal by someone who has considerable experience in observing horses with neurological deficits. A grade 2 can be seen by most people, but only if the horse is really taxed to do something challenging – such as walking backward down a ramp, or turning in tight circles. A grade 3 has obvious abnormalities doing ordinary things, such as walking in a straight line. A grade 4 is so abnormal that you don't even have to take that horse out of the stall – you look in the stall and there he is, with his legs crossed, or pressing his head into the wall, or walking in circles – he pretty much has a sign on him that says 'I'm neurological. It's a simplistic grading system, but it works fairly well. Let's continue with our examination to determine which of these categories Koenig fits into.