Several diseases can affect the horse’s central nervous system (CNS), with signs that can vary from mild gait abnormalities to a complete loss of body function control. Our Leatherstocking Veterinary Services team offers information about four common equine neurologic diseases should your horse be affected.
Cervical vertebral stenotic myelopathy in horses
Commonly called wobbler syndrome, cervical vertebral stenotic myelopathy (CVSM) is a developmental defect that affects the horse’s cervical vertebrae and causes lesions that lead to spinal compression and potential spinal damage. Possible contributors include genetic traits, diet, growth rate, workload, and injury. CVSM is one of the most common causes of incoordination in young sport horses, and older horses can develop bony changes in their neck that lead to neurologic signs. CVSM details include:
- Clinical signs — Initial signs, which include neck stiffness and incoordination, are typically mild, but the incoordination becomes more severe as the condition progresses, and the horse may start dragging their feet and have a decreased range of motion. Deficits are usually more severe in the hind limbs.
- Diagnosis — Diagnosis is based on your horse’s history, a thorough neurologic exam, and neck X-rays. In some cases, more advanced imaging is required for definitive diagnosis.
- Treatment — Depending on the lesion’s location and severity, treatment can be medical or surgical. Medical treatment involves rest and systemic or local anti-inflammatory medications, while surgical treatment focuses on stabilizing the affected area.
- Prognosis — Severely affected horses are unlikely to regain normal neurologic function. Young, mildly affected horses who exhibit clinical signs for only a short period have the best chance of returning to normal performance levels.
- Prevention — Since the condition seems inherited, affected horses should not be bred. Young horses need a nutritionally balanced diet to prevent accelerated growth rates, and an appropriate workload to ensure they experience no trauma.
Equine protozoal myeloencephalitis in horses
Equine protozoal myeloencephalitis (EPM) is an infection caused by the protozoan Sarcocystis neurona that affects a horse’s CNS. Opossums are the definitive parasite host, and shed the infective sporocysts in their feces. Horses become infected when they ingest water or food contaminated by opossum feces. In susceptible horses, the sporocysts migrate from the intestinal tract to the bloodstream, cross the blood brain barrier, and attack the CNS. EPM details include:
- Clinical signs — Clinical signs depend on the part of the CNS affected. When the spinal cord is involved, signs include gait abnormalities, incoordination, ataxia, and muscle atrophy. When the brain is involved, signs can include lethargy, behavioral changes, head tilt, facial nerve paralysis, and difficulty swallowing.
- Diagnosis — EPM is diagnosed by ruling out other potential neurologic disorders, a neurologic examination, and finding S. neurona antibodies in the horse’s serum or cerebrospinal fluid (CSF).
- Treatment — A Food and Drug Administration (FDA)-approved drug is available to treat EPM. Supportive treatment may also be needed, depending on the disease severity.
- Prognosis — Most treated horses improve, and some recover completely, but about 10% to 20% of horses relapse within two years. Prompt diagnosis and treatment is important to maximize the horse’s recovery.
- Prevention — Preventive measures involve reducing opossum feces exposure by not feeding horses on the ground, cleaning water troughs regularly, keeping feed containers sealed, and cleaning up dropped grain as soon as possible to discourage scavengers.
Equine degenerative myeloencephalopathy in horses
Equine degenerative myeloencephalopathy (EDM) and equine neuroaxonal dystrophy (eNAD), a related disease, are caused by abnormalities to specific brainstem and spinal cord neurons. Studies indicate a genetic basis for these diseases, and Appaloosas, Morgans, Standardbreds, Quarter horses, and Lusitanos seem at higher risk. Signs occur if the horse has a dietary vitamin E deficiency during specific developmental stages. EDM details include:
- Clinical signs — Signs vary from mild performance issues to severe debilitation, and often manifest in horses from 6 to 24 months of age.
- Diagnosis — EDM diagnosis involves a thorough neurologic examination, ruling out other potential causes, and finding low vitamin E blood levels.
- Treatment — Dietary vitamin E supplementation can slow or halt, but not reverse, disease progression.
- Prognosis — Mildly affected horses can be kept as pasture pets, but those with severe clinical signs are usually euthanized.
- Prevention — The best vitamin E source is fresh green grass, and horses who do not have year-round access to fresh pasture should receive vitamin E supplementation in their diet.
Equine herpesvirus myeloencephalopathy in horses
Equine herpesvirus myeloencephalopathy (EHM) occurs when the equine herpesvirus-1 (EHV-1) attacks the horse’s spinal cord and brain. The virus is spread through direct horse-to-horse contact, contaminated hands and equipment, and aerosolized viral particles. Some infected horses show no clinical signs, but act as carriers to spread the disease. EHM details include:
- Clinical signs — Initial signs typically include fever, nasal discharge, and cough. Neurologic signs typically occur about 8 to 12 days after the primary infection, with signs that include lethargy, weakness, incoordination, difficulty standing, dog-sitting, and coma.
- Diagnosis — EHV-1 DNA can be detected in nasal secretions and blood samples using a polymerase chain reaction (PCR) test.
- Treatment — Affected horses should be isolated immediately to prevent virus spread. Treatment is supportive, and includes fluids, anti-inflammatories, and slings if the horse can’t stand on their own.
- Prognosis — EHM’s mortality rate is 30% to 50%. Horses who can stand on their own have a better prognosis.
- Prevention — Vaccines are available for the respiratory and abortion EHV forms, but not for EHM. Prevention involves following basic biosecurity guidelines to decrease the potential disease spread.
Diseases affecting a horse’s CNS are concerning, and promptly determining the underlying cause is important. If your horse is exhibiting gait abnormalities, incoordination, or other concerning signs, contact our Leatherstocking Veterinary Services team, so we can diagnose the issue and ensure they get the care they need.