Know the Signs of EPM, a Master of Disguise

With an early diagnosis and prompt treatment, horses can improve significantly and could return to normal activity.

No account yet? Register


Know the Signs of EPM, a Master of Disguise
In addition to an altered gait, horses with EPM can have paralysis of muscles of the eyes, face, or mouth, evident by drooping eyes, ears, or lips. | Photo: Noah D. Cohen, VMD, PPH, PhD, Dipl. ACVIM

Equine protozoal myeloencephalitis (EPM) is a debilitating neurologic disease that cannot be ignored. More than half of all horses in the United States—and in some areas as many as 90%—have been exposed to the disease’s causative agents. Its ability to masquerade as other health issues, such as lameness or other neurologic diseases, can make it difficult to diagnose.

While Sarah Reuss, VMD, Dip. ACVIM, of Merial Veterinary Services, says some horses exposed to EPM’s causative agents will not develop the clinical disease, horses under stress are more likely to show signs. In some cases, horses can even be infected without showing signs for months or years or ever. When horses do show signs, it can go misdiagnosed because it can slowly progress and infect any portion of the central neurologic system, mimicking other conditions.

Left untreated, EPM can lead to permanent damage

Create a free account with to view this content. is home to thousands of free articles about horse health care. In order to access some of our exclusive free content, you must be signed into

Start your free account today!

Already have an account?
and continue reading.


Written by:

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from

Sponsored Content

Weekly Poll

sponsored by:

What do you think: Can pituitary pars intermedia dysfunction (PPID) be managed by medication alone?
126 votes · 126 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form

Create a free account with!