Neurologic Disorders: The Warning Signs
Knowing the the signs of a possible nervous-system issue can mean the difference between recovery and lingering disability (or worse) for your horse.
Learn to recognize the red flags of a nervous-system issue early as well as what you can do to get your horse on the road to recovery.
Your horse just isn’t quite right. His performance has been a little off lately, you’ve noticed him stumbling now and then, and he seems to be losing muscle over his topline. He’s not actually lame. So what’s going on?
With symptoms like those, there’s
a good chance your horse might be facing a neurological disorder. Many things—including trauma, degenerative conditions, viruses and parasites—can disrupt the signals flowing along your horse’s spinal cord from the brain to the nerves and muscles.
“Detecting symptoms early increases the likelihood of successful treatment and recovery,” says the University of Pennsylvania New Bolton Center’s assistant professor Amy L. Johnson, DVM, DACVIM in both internal medicine and neurology. That’s because neurological disorders affect neurons (nerve cells), and “once neurons are destroyed, they don’t regenerate,” says Dr. Johnson.
If a neurologic disorder is left untreated, she adds, more neurons become affected and more of them die.
“Horses can compensate for losing some neurons, but once a critical number are lost, normal function will never return. And almost all neurological diseases can be fatal, depending on the severity and whether or not treatment is provided.”
That’s why it’s critical for horse owners to know the signs of potential neurologic trouble and act quickly to bring a vet onto the scene. Here, Dr. Johnson shares red flags to watch for, plus an inside perspective on what your vet will do to pinpoint the trouble and put your horse on the road to recovery.
Signs to Watch For
“The most common indication of a neurologic problem in horses is some degree of clumsiness or incoordination,” says Dr. Johnson. That’s because neurologic disorders often affect the spinal cord, which delivers messages to all of the horse’s limbs. So you might notice your horse standing in unusual positions—say, with his legs crossed or placed more widely than usual. Or your horse might trip, stumble, move more slowly than normal or have trouble performing his regular work.
Other neurological disorders affect the brain. If the front brain is involved, you may spot alterations in your horse’s behavior and mental status, says Dr. Johnson. For instance, she adds, “If your 3-year-old Thoroughbred is acting like a 20-year-old pony, that could be an indication of trouble.” Other signs of a front-brain problem include obsessive circling, aimless wandering and staggering.
“If the problem is in the back part of the brain, or the brain stem, the horse may have an unusual appearance to his face, similar to a person who has suffered a stroke,” says Dr. Johnson. “You may see drooping of an ear or eyelid, the nose pulled to one side, a tilt to the head. The horse may have trouble eating or drinking, even to the point where food is coming out the nose.”
Other general signs of potential neurological trouble include muscle loss, often on one or both hips, or over the topline. Your horse may not swish his tail or twitch his skin like he normally does—for example, to keep flies off. You may see an overall drop in condition or your horse may suddenly have trouble maintaining weight or may lose his appetite. Certain disorders could contribute to neck pain, leading your horse to resist bending his neck or raising/lowering his head, or causing a loss of suppleness.
If you notice any of these signs, it’s time to call the vet.
What to Expect from Your Vet
When your vet arrives on site, expect her to start with a basic physical exam, taking your horse’s heart rate, respiratory rate and temperature and checking for gut sounds. At this stage, the vet is looking to eliminate the possibility of a systemic (body-wide) disease, such as septicemia (bacteria or toxins in the bloodstream) or equine infectious anemia. says Dr. Johnson, because “most neurological disorders don’t cause systemic problems, but systemic disease can occasionally make a horse look neurologic.”
Your vet will also ask you to discuss the symptoms you’ve seen, including changes in your horse’s personality, such as lethargy or aggression. Share as much detail as you can on the circumstances, such as when the signs started and how often they occur. Your horse’s age and breed may also play a role, since some
neurological problems tend to be more common in certain groups.
Your vet will also take in the big picture, looking your horse over for any signs of asymmetry in posture or muscling, muscle atrophy or lack of condition.
Your vet will then begin conducting specific tests to pinpoint whether your horse’s problems are related to a neurological disorder and, if so, which part of the nervous system is most likely the source of trouble. These tests typically include procedures to check facial reflexes, body reflexes and your horse’s gaits and posture.
“There are 12 cranial nerves that influence the horse’s ability to see, chew, swallow and have symmetrical expressions, among other things,” says Dr. Johnson. To test how well these nerves are doing their job, she notes, your vet may conduct any of a number of tests on both sides of the horse (where applicable). Here are a few examples:
Testing your horse’s “menace response.” The vet moves her hand quickly toward the horse’s eye to see whether he blinks. This tests the horse’s ability to see and to close his eyelids.
Checking for skin sensation. The vet taps along the side of the horse’s face, from the ear to the nostril. The horse should blink and/or attempt to move away from the tapping.
Testing the ability to chew and swallow. The vet may give the horse a treat or watch the horse eat and drink.
Testing tongue strength and func-
tion. The vet gently pulls the horse’s tongue out through the bars on one side of the mouth and then watches to see if the horse can pull it back in.
Again, the vet may perform any or all of the following tests on both sides of your horse to check for normal responses. Typically, a lack of reaction to any test or in a specific area indicates that nerve signals may not be reaching that location.
Neck range of motion. The vet may encourage your horse to bend his neck to each side, stretching toward the hip, stifle or hock, or down between the front legs, often using a carrot or other treat as an in- centive. If your horse has trouble with this exercise, it could indicate an injury to his neck, such as a fractured vertebra or neck arthritis. Other indications of neck trouble include difficulty raising the head, holding the head or neck in an unusual position,
loss of suppleness through the neck and reluctance to bend during work.
Skin sensation. Your vet will lightly run or tap a pen along your horse’s skin to watch for a twitching response—the reaction your horse would have to a fly landing on his skin.
Reaction to pressure. Your vet will palpate your horse’s topline, neck, chest, hindquarters and stifles to see if he moves away from the pressure or otherwise reacts.
Tail tone and body strength/coordination. A horse’s tail receives nerve signals from the spinal cord, so your vet will also conduct tests to make sure those messages are getting delivered. For instance, she may lift the tail to check for resistance; if the tail is limp, that’s a sign of trouble. To test your horse’s body strength and coordination, she may also pull the tail gently to each side while your horse is standing and/or walking. If the pull shifts your horse off balance, that’s another red flag.
Gait and Posture Assessment
In the next stage of a neurological evaluation, your vet will assess your horse’s gaits and posture. In general, these tests will show whether the horse knows where his feet are and has normal control over his limbs.
Your vet may ask you to walk your horse on varying surfaces, up or down a slope and a curb or step, in a tight circle in each direction and to back up. She may want to see your horse moving freely in a round pen as well as moving in hand. She’ll watch to see if your horse stumbles, sways, staggers, drags his toes, swings a hind leg, steps on himself or shows other signs of incoordination or gait abnormalities.
Your vet may also pick up one of your
horse’s feet and place it so it crosses in front of its opposite. For example, she may lift the left front and place it over the right front. A horse with a neurological problem may leave the foot out of place for a while before moving it back into position.
Going to the Next Level
By this point in the exam, your vet will probably have a strong sense of whether your horse has a neurological problem, says Dr. Johnson. If the issue doesn’t seem neurologic, she adds, the vet will carry on looking for other possible causes for what you’re seeing, such as conducting a lameness exam or oral exam because problems with chewing and swallowing, for instance, can be caused by dental troubles.
If your vet decides there is a neurologic disorder, the next challenge is determining the underlying cause. It’s not as simple as you might think. “The actual neurologic signs the horse shows depend almost en- tirely on what part of the nervous system is affected, rather than the disease itself,” says Dr. Johnson. “In other words, the neurologic signs of brain injury can be similar regardless of whether the brain is injured due to trauma, abnormal liver function or infection such as equine protozoal myeloencephalitis. However, other signs might help identify the underlying cause.”
Following are several examples of common neurological disorders and the symptoms and diagnostic aids that can help your vet distinguish one from another.
If your horse has experienced an injury to the skull or any part of the spine—for instance, from hitting his head or falling— that’s a strong indication that trauma could be the trouble. Symptoms of a problem could be immediate, such as unconsciousness, disorientation or temporary blindness. Or they may not appear for a while and then could include trouble getting up
or lack of coordination.
Diagnostics: Radiographs (X-rays) to check for possible fractures of the skull or spinal vertebrae.
Equine Protozoal Myeloencephalitis
Loss of coordination is one of the most common symptoms of EPM along with muscle atrophy affecting only one side of the horse, says Dr. Johnson. EPM horses may also show signs of back brainstem impairment, such as partial facial paralysis and trouble swallowing.
Diagnostics: Blood and spinal-fluid tests to look for antibodies to the EPMcausing parasite. Both tests are recommended because in areas where EPM is prevalent, it’s not uncommon for 50 percent or more of the equine population to have antibodies to the disease. That could cause a positive blood test even if a horse isn’t infected, explains Dr. Johnson. If the antibodies are also present in spinal fluid at an increased level compared to blood, that provides a much more accurate diagnosis, she says.
EHV-1 is more commonly seen in outbreaks involving a number of individuals, says Dr. Johnson. So if multiple horses in an area start exhibiting similar symptoms, that’s an indication this disease could be the culprit. Affected horses may run a fever and lose control over when they urinate or pass manure (urinary and/or fecal incontinence). They may show weakness in their tail muscles. The back legs are more often affected, which can lead to the horse having trouble rising and, instead, taking on a “sitting dog” position partway up.
Diagnostics: Polymerase chain-reaction tests to identify the virus in blood samples or nasal swabs. (A PCR test allows the vet to analyze viral DNA even when very small amounts are present in a sample.)
Officially known as cervical vertebral stenotic myelopathy or cervical vertebral malformation, “wobblers is a problem with the vertebral column in the region of the neck,” says Dr. Johnson. Specifically, abnormal vertebrae cause compression on the spinal
cord, which can block nerve signals.
“Symptoms tend to be in all four limbs, although they may be more evident in the back legs,” says Dr. Johnson. She adds that the disease can look a lot like EPM, but wobbler horses might have neck pain while EPM horses won’t.
Diagnostics: Blood and spinal-fluid tests to rule out EPM, radiographs to eliminate a vertebral fracture and show vertebral changes suggestive of wobbler syndrome and/or a myelogram (see sidebar on page 55) to identify pressure on the spinal cord.
Eastern and Western Equine Encephalomyelitis, West Nile Virus
These mosquito-borne diseases all affect the horse’s spinal cord and brain, says Dr. Johnson. “They have symptoms indicative of brain problems—weird behavior, they may lose the ability to stand up, they may have fevers,” she adds. The horse may also exhibit head-pressing (literally, the horse presses his head against a surface such as a stall wall) and aimless wandering, lose his appetite, appear depressed, have impaired vision or show muscle twitching and hindlimb weakness. Dr. Johnson notes that horses with West Nile virus may present with more spinal symptoms than EEE or WEE horses but almost always have brain signs as well.
Diagnostics: Blood and spinal-fluid tests are taken by your veterinarian.
Since it may take days to get results from diagnostic tests (and even then more advanced testing may be needed), your vet may start your horse on an initial treatment plan immediately. This might include therapies directly aimed at the suspected disorder (see sidebar on page 56). Or it may focus on supportive treatments—such as intravenous fluids or anti-inflammatories—to keep your horse comfortable and as stable as possible until a final diagnosis is made.
This inherent delay in the process is just one more reason it’s important for you to know the symptoms of neurological trouble. Then you can start the ball rolling quickly on a diagnosis so treatments can begin and your horse can start his journey to recovery.
ABOVE: If your vet thinks that your horse could have a neurological issue, she will perform tests to assess his strength and coordination, such as pulling his tail gently to the side when he’s walking and seeing if it affects his balance.
RIGHT: A horse suffering from a neurological disorder can often appear weak and unsteady on his feet.
Because neurologic disorders often affect the horse’s spinal column and subsequently his limbs, you might notice him standing in an unusual wide-legged position or even stumbling or crossing his legs when he walks.
If a horse’s neurologic problem is in the brain stem, he could have a strange drooping or asymmetrical appearance to his facial features, similar to a person who had a stroke.
To check a horse’s facial reflexes, a vet may test a menace response by moving her hand quickly toward his eye to see if he blinks.
To check your horse’s body reflexes, a vet will likely conduct a neck stretch test in both directions (usually with a carrot as an incentive) to observe the suppleness of the neck and rule out any possible trauma or arthritis concerns.
Your vet may want to watch your horse walk up or down a hill or on uneven surfaces in order to analyze his gait and posture and note any stumbling or weakness.
One of the best ways to determine if your horse has sustained a fracture is for your vet to take radiographs of his spine or skull.
Blood tests can help with proper diagnosis of neurologic diseases such as EPM, EHV-1, EEE, WEE and West Nile virus.