Worrisome Wobbling – What to do for the neurologic horse was the subject of a March 5 presentation at Penn Vet’s New Bolton Center by Amy L. Johnson, DVM, DACVIM – LAIM and Neurology. Dr. Johnson is one of a small handful of veterinarians in the world board-certified in both large animal internal medicine and neurology. She is an assistant professor at the University of Pennsylvania School of Veterinary Medicine, based at Penn Vet’s New Bolton Center campus in Kennett Square, PA. The lecture was part of the First Tuesday Lecture series at New Bolton Center, offering the public open lectures on equine topics, at no charge, the first Tuesday of each month.
Neurologic: What Does it Mean?
The presentation began with an overview of equine neurology. A neurologic horse has a problem somewhere in its nervous system. Structurally, the nervous system is comprised of the brain, cranial nerves, spinal cord, and peripheral nerves. Functionally, the nervous system controls everything in the body. This includes the horse’s ability to learn and process information; the horse’s vision, smell, taste, and hearing; coordination and balance; limb movements and muscle strength; and basic bodily functions such as urination and defecation. When there is a problem with the nervous system, the horse will lose control of part of its body. If control of limb movements, strength, coordination, or balance is lost, serious injury to the horse or rider may result. Although this “loss of control” sounds terrifying, neurologic disease can cause a spectrum of disease ranging from inconsequential or mildly incapacitating problems to performance-limiting, hazardous, or even life-threatening problems.
Since many neurologic diseases are progressive, it is important for owners to identify and try to diagnose neurologic problems early. Signs of neurologic disease include behavior changes, loss of symmetry, particularly in facial expression or muscling; difficulty with basic functions such as eating, drinking, urinating, or defecating; abnormal posture; lack of coordination; and weakness. If you think a horse may be showing signs of neurologic disease, the first thing to consider is safety. The horse should be kept or moved to a safe environment, such as a stall. Children and inexperienced people should not be allowed to handle the horse. Contact with the affected horse should be limited if the horse has a fever or shows behavior changes. Isolating the affected horse will help to prevent transmission of EHV-1 (equine herpes virus 1) to other horses if that virus is causing the neurologic disease. Limiting contact with people could prevent exposure to rabies if that virus is the cause. In addition to addressing these safety measures, you should involve your veterinarian right away with suspected cases of neurologic disease.
Narrowing the Diagnosis
Your veterinarian’s job is to perform a complete neurologic exam and determine whether the nervous system is normal or abnormal. If it is abnormal, your vet will try to narrow down which part is affected, and based on this localization, will make a list of likely diseases that may be affecting that part. Based on this list of differential diagnoses, your vet will choose which tests to perform to try to identify which disease is present. Many of these tests may require referral to a specialty hospital such as New Bolton Center. Finally, your vet will design a treatment protocol. Depending on the severity or nature of the horse’s neurologic disease, effective treatment may also require referral.
One reason for referral to a specialty hospital is that many of the diagnostic tests recommended for horses with neurologic disease may be difficult or impossible to perform in a barn. These tests, all of which are commonly performed at New Bolton Center, include digital radiographs or x-rays of the horse’s vertebral column, or spine; myelography, during which the horse is placed under general anesthesia and a contrast agent is injected into the space around the spinal cord so that additional radiographs will show exactly where the spinal cord is located and whether it is being pinched/compressed by bones or other structures; spinal taps; and advanced brain imaging using MRI or CT scans. Facilities like New Bolton Center also have specialized equipment, such as hoists and slings, allowing us to help very weak horses or those horses unable to stand. Finally, New Bolton Center has an isolation facility so that we can safely provide care for contagious or dangerous horses.
Don’t Just Treat for EPM
Many owners ask, “Why shouldn’t I just treat my horse for EPM if it is showing neurologic signs?” EPM, or equine protozoal myeloencephalitis, is a relatively common cause of neurologic disease in this area. However, it is certainly not the only cause. There are many other causes of neurologic disease, many of which cause very similar signs and can easily be confused with EPM. Treatment for EPM can be quite expensive; a two-month treatment course often costs close to $2000. If owners “just treat for EPM” rather than seeking an accurate diagnosis first, they may find that they have wasted time and money, as well as delaying an accurate diagnosis, if the horse doesn’t look any better after one to two months of treatment. At New Bolton Center, EPM is the cause of less than half of our cases of neurologic disease.
After providing an overview of equine neurology, Dr. Johnson presented several case studies illustrating various neurologic conditions. These included cases of cervical vertebral malformation (Wobblers disease), EPM, West Nile virus, Rabies, and the equine equivalent of a stroke. Attendees were reminded that they should “prevent the preventable,” as many neurologic diseases can be prevented through appropriate vaccination. Important vaccines include those for EEE (eastern equine encephalomyelitis), WEE (western equine encephalomyelitis), tetanus, botulism, West Nile virus, and Rabies. There is currently no effective vaccine for EPM. The vaccine for EHV-1 can help prevent spread of the virus but does not reliably prevent neurologic disease.
Future First Tuesday lectures include: April 2, Dr. Lawrence Soma, The Dope on New Drug Research and Testing; May 7, Patrick Reilly, chief of farrier services, The Penn Vet Podological Museum: the farrier-vet connection through the years; June 4, Dr. Mariana Crumley, Down for the Count: the science and art of general anesthesia in horses.