Equine Protozoal Myeloencephalitis (EPM) is one of the most feared diseases among horse owners – so feared that owners might be tempted to request their veterinarian treat their horse for EPM without proper diagnostic measures. While early treatment is critical to stopping the disease from causing further nerve damage, if the horse does not have EPM, an EPM treatment product will not be effective.
Amy Johnson, DVM, Dipl. ACVIM, assistant professor of large animal medicine and neurology at the New Bolton Center at the University of Pennsylvania, said treating EPM without a diagnosis can cost owners money and time.
“Many diseases can cause signs similar to EPM, but will not respond to EPM treatment. If the horse is treated for EPM, but actually has another disease, the owners have not only wasted their money, but also time that could have been better used pursuing the true cause of the horse’s problem,” Johnson said.
Stephen Reed, DVM, Dipl. ACVIM, internal medicine veterinarian at Rood and Riddle Equine Hospital in Lexington, Kentucky, agreed with Johnson.
“Signs of EPM can vary from neurologic to a mysterious lameness, so a thorough diagnostic work-up is really critical to make sure we are treating the horse appropriately and thus, improving his chances of recovering,” Reed said.
Diagnosing EPM in a living horse can be tricky because the clinical signs are variable, but it is time and money well spent.
“The best way we know to diagnose EPM in a living horse is the combination of a thorough neurologic exam, antibody testing and appropriate diagnostic testing to rule out other diseases that can also cause neurologic signs,” Johnson said.
There are several diseases that cause neurologic signs in the horse similar to EPM, but all are treated differently.
“West Nile virus, rabies, tetanus, wobbler syndrome, eastern and Western equine encephalitis, equine herpes myeloencephalopathy (EHM), and even trauma can all cause neurologic deficits in horses,” Merck Animal Heath equine technical services veterinarian Wendy Vaala, VMD, Dipl. ACVIM, said. “Without thoroughly evaluating the horse and performing appropriate diagnostic tests, we can’t effectively treat them.”
“Currently, the recommendation for antibody testing is to collect spinal fluid and blood samples and compare the antibody titers in each to determine if there is evidence of a central nervous system infection,” Johnson added. “If spinal fluid is not feasible, it is reasonable to only collect a blood sample.”
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