The Neurological Examination – Part I
Dr. Melissa Mazan
At the end of the examination, your veterinarian may feel that she has adequate information to diagnose the problem, or she may feel that she still needs additional information. The most common ancillary tests include x-rays of the cervical spine, a myelogram, and a cerebrospinal fluid analysis.
The portions of the horse's body that are easily accessible to x-rays include the skull and the C-spine. Other areas are too thick for even the most penetrating X-ray beam, or will require general anesthesia to obtain the correct exposure. With X-rays, your veterinarian can look for signs of trauma, developmental bone disease that impinges on the spinal cord (Wobbler's Syndrome) or arthritis.
The myelogram must be done under general anesthesia. In this procedure, X-rays of the horse's spine are taken while a contrast agent is placed in the space surrounding the spinal cord. This involves some risk to the horse, as the contrast agent must be placed into the atlanto-occipital space – a little bit behind the level of the horse's ears. There is a portion of the brain at this area, so the veterinarian must be very careful not to hit the brain with the needle that is used to place the contrast agent into the space. After the contrast agent is placed, x-rays are taken while the neck is manipulated in order to see if the spinal cord becomes pinched during these maneuvers – thus confirming a diagnosis of Wobbler's Syndrome.
Cerebrospinal Fluid Analysis
In this procedure, a spinal tap, a small amount of fluid is removed from the area surrounding the spinal cord. This can be done in the standing, sedated horse, from the lumbosacral space (roughly at the level of the highest point of the croup) or in the anesthetized horse from the atlanto-occipital space. It is less risky to the horse to retrieve the fluid from the lumbosacral space, but more risky to the person performing the maneuver – every once in a while, a horse will have a strong reaction to the tap. The fluid can be analyzed for abnormal protein, cells, or evidence of diseases such as equine protozoal myeloencephalopathy (EPM).
Other tests include the EEG, which measures the electrical activity of the brain, or brain waves, the electromyelogram, which tells us about the electrical activity of muscle cells and the nerves that control those cells, nerve conduction tests, which tell us about the way that signals are going through peripheral nerves, and computed tomography (CT scan), which can give us a more detailed picture of the brain, skull, vertebrae, and spinal cord than an x-ray can.
Neurologic disease can be puzzling, and difficult for even experienced veterinarians to diagnose. However, with a careful, methodical neurologic examination and selected ancillary tests, the detective can find the right clues, and the mystery can be solved.