Veterinarians in the field often have to perform a neurologic horse diagnosis. Amy Johnson, DVM, DACVIM (Large Animal and Neurology), spoke on “Diagnosing the Neurologic Horse in the Field” at the 2021 AAEP Convention. Johnson is an Associate Professor of Medicine & Neurology and Section Chief, Internal Medicine & Ophthalmology, at the University of Pennsylvania School of Veterinary Medicine.
Johnson’s first advice in this podcast is to tell owners to not panic if you diagnose a horse as neurologic. She said there are two different categories of neurologic horses. The first contains those neurologic horses that need emergency care immediately. The second category are those horses diagnosed as neurologic but are not emergencies.
Neurologic Horse: First Steps
Some items veterinarians should evaluate even before they see a neurologic horse include vaccination history, Johnson said. This is especially true if the horse is not a normal patient. Rabies is often a differential diagnosis for a neurologic horse, so it is a concern.
There are many diseases that can cause neurologic signs in horses. Johnson said equine veterinarians need to go through to differential diagnoses. That includes conducting physical and mental evaluations of the horse.
“You also need to include potential lameness in multiple limbs,” she said. “Even good veterinarians can mistake a hind limb lameness for neurologic signs. Don’t jump to a differential.”
She said after physical, mental and neurologic exams, veterinarians should determine if the cause of the horse’s issues is neurologic. Then they should localize the lesion with the understanding that different diseases target different areas of the central nervous system.
“That also plays into the initial treatment,” Johnson added. “EPM, West Nile virus, herpesvirus, neurologic Lyme disease, trauma to the nervous system, generative diseases…those are all on my list based on the region. Other regions might indicate botulism, EPM or Lyme disease.”
Other differentials based on location of the lesion could be wobbler syndrome or equine degenerative myeloencephalopathy (EDM).
Testing Neurologic Horses
Johnson acknowledged that there are limited diagnostic tests that can be done in the field. “Safety concerns come into play,” she noted. “Some horses you can hardly examine in some facilities. Human safety is number one; horses are second and equipment is third.”
She said on the farm you often can do a neurologic exam on the horse if it is safe. You can take a blood sample, but she said rarely does that help you identify a neurologic problem. However, Johnson said if the hores has enecphalitis it could shold up in liver values.
She advised veterinarians to check the nasal structures for injury and take a swab for herpesvirus.
“It’s hard to radiograph a horse’s head or neck in the field because of the lack of power [in the portable equipment],” she noted.
“Some vets are okay with doing a spinal tap in the field, and some are not,” Johnson added.
Other testing could include PCR, where you are looking for antibodies for diseases such as EPM or neurologic Lyme disease. Johnson reminded
When You Should Isolate
“Where I practice, rabies is endemic,” said Johnson. “You’re worried about human exposure.”
She said not many rabies cases are neurologic, but some show up as lameness or colic or some other clinical sign, then morph into more typical rabies signs.
“If rabies vaccination history is poor, limit people expose and wear gloves and a face mask to prevent horse saliva from human mucous membranes,” she warned.
There is the potential for contagious neurologic diseases—such as herpesvirus—to be spread horse-to-horse.
“If any horse in the barn has a fever, suspect an infectious virus,” Johnson advised. “You can also look for signs of respiratory infection or abortions in broodmares.
Johnson described the advancement of neurologic signs in a horse with herpesvirus.
She said any horses suspected of having an infectious or contagious disease should be isolated with proper biosecurity measures taken.
Veterinarians need to know their state laws for reportable diseases, said Johnson. If you suspect a disease that is reportable in your state, then you need to know what steps to take. The state veterinarian might tell you what those steps are. Even before you diagnose a neurologic disease in a horse, you need to report your suspicions.
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