Equine Science Class Learns about Neurological Disorders in Equines

Tuesday Talks are a lecture series hosted by the Virginia Tech Marion duPont Scott Equine Medical Center offering the opportunity to learn about a variety of equine health topics from Equine Medical Center clinicians, residents, and guest speakers. 

by Nia D. ’22

For this week's Tuesday Talk, our Equine Science class learned about neurological disorders in equines from Dr. Krista Estell, Clinical Assistant Professor of Equine Medicine at the Marion duPont Scott Equine Medical Center, who has a special interest in cardiology and oncology in addition to neurology. She began the talk by speaking about the basic anatomy of the spine and spinal cord. The spinal cord is basically a soft cylindrical tissue that connects the brain to the rest of the body and there are nerves that enter and exit the spinal cord between the vertebrae. The spinal cord is also cushioned by cerebral fluid to protect it from the surrounding bone.
After discussing the basic anatomy of the spinal cord, she moved on to the process she goes through while giving a horse a neurological exam. First, she evaluates the horse’s stance and mental status. Usually, if a horse is standing awkwardly with its limbs going every which way, it is a clear indicator that the horse is not fully aware of where its limbs are, which is caused by some sort of neck or head trauma. Second, she conducts palpitation and flexion of the entire neck and back. Then she moves on to dynamic evaluation of the horse’s gate under normal conditions and special circumstances (i.e. moving up and down hills) to see if there is any irregularity. Finally, she will examine whether or not the horse’s motor function and sensory perception are normal. 

Dr. Estell then talked about how to pinpoint where the problem originates along the spine based on the horse's symptoms. Most problems originate from C1-C6 (cervical vertebrae 1-6) and C6-T2 (cervical vertebrae 2- thoracic vertebrae 2), which cause problems in all the limbs. After talking about the diagnostic process, she began describing the common spinal cord diseases of the horse, which include: trauma, cervical stenotic myelopathy (spinal cord compression), wobbler disease, osteoarthritis, and Equine Protozoal Myeloencephalopathy (EPM). 

Dr. Estell then moved on to the traumatic brain and spinal cord injuries of the horse. She emphasized how important physical and neurological examinations are in the process of acquiring an accurate diagnosis. Diagnostic imaging can also help identify any fractures in either the skull or vertebrae and radiographs are difficult to read because the skull and vertebral column are complex and three-dimensional. Dr. Estell was very fond of the CT scan (computed tomography scan) which scans small slices of the image and allows them to be pieced together to create a detailed 3D image which is crucial in accurately identifying and solving the problem. She then showed us some very interesting CT scans of a yearling (year old horse) who had run full tilt into a solid object and walked us through how she both pinpointed the problem and was able to image it clearly in order to help the yearling. 

We then moved to the topic of cervical stenotic myelopathy, more commonly known as wobbler disease. Wobbler disease is a compression of the spinal cord as a result of either congenital malformation-malarticulation or the development of osteoarthritis in the articular facet joints of the vertebral column. Dr. Estell shared some images of different diagnostic methods. The first was an injection of contrast agent in the cerebrospinal fluid (CSF) to see a clear outline of the spinal cord. The second was also a CT scan method, where they also inject a contrast agent into the CSF, but they are able to get a 360 view of the entire spinal cord, which is awesome! 

Dr. Estell continued her presentation with a discussion of Equine Protozoal Myeloencephalopathy (EPM). Unlike the other spinal cord and brain issues, EPM is caused by one of two microbes. The most common one is Sarcocystis neurona which is carried by opossums. The more rare carrier is called Neospora hughesi and very little information has been found on this microbe. With Sarcocystis neurona the host will poo in horse feed and then the horse will ingest its feces on accident and become infected with EPM. Some of the classic signs of EPM are asymmetric muscle atrophy (uneven muscle loss), degrees of ataxia, and conscious proprioceptive deficits/weakness. EPM has also been known to cause brain and brainstem diseases. She then clarified the distinction between infection vs. the disease of EPM. The exposure rates in Maryland and Virginia are so high that 80-90% of horses have antibodies for Sarcocystis neurona but only a small number of horses actually develop the disease associated with the microbe. Because of this high antibody presence in equines, blood testing is not enough for a definitive EPM diagnosis. To overcome this diagnosis obstacle, veterinarians take samples of the blood and CSF fluid and compare the ratio of both to see if it is greater than 100. If so, that does not correlate with an EPM diagnosis. 

Dr. Estell then talked about different forms of treatment for EPM which include Marquis (a daily paste given to the horse) and Protazil (a topdressing that can be given as a half dose daily or three times per week). We also discussed when it is appropriate to stop treatment; she recommended around two months of treatment before taking the horse off of medication. Even after treatment, there are lasting effects on the horse. Seventy percent of horses do not return to their previous level of work, some never fully recover, and some even relapse after being taken off the medicine. Dr. Estell closed her presentation with a brief look forward into possible diagnostic and treatment methods of EPM that could help further the effectiveness of EPM treatment.  
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