Texas Equine Veterinary Association

• 19 • Equine protozoal myeloencephalitis (EPM) continues to be one of the most challenging maladies practitioners face, particularly when it comes to identification and diagnosis. e temptation to "treat and see" without a complete diagnostic picture can be tough to resist. However, with so many diseases causing clinical signs similar to EPM, it's an urge practitioners must avoid. If a horse has a disease other than EPM, not only have we wasted money on unnecessary treat- ment, but also time that could have been better used pursuing the true cause of the horse's problem. Our diagnostic approaches to EPM have come a long way, as has our understanding of the causes. Reliable quantitative testing coupled with practical hands-on examination principles can help practitioners gain confidence in their EPM diagnosis. What defines an EPM suspect case? e best initial course of action is a combination of reviewing the horse's health history and performing a thorough physical and neurologic exam. Any region within the central nervous system (CNS) can become parasitized, and the clinical signs may vary depending on which part of the nervous system is impacted. Asymmetry is a telltale marker of a suspected EPM case. It is a progressive, multi-focal disease, oen with muscle atrophy. ese signs along with ataxia and dysmetria are the most common clini- cal signs to watch for in EPM cases. Let's walk through a very basic "if-then" scenario to gain a clearer picture of a proper diagnostic workup in a suspect case. Upon physical and neurologic evaluation: a) Does the horse have a history of EPM or has EPM been diagnosed in the resident population? a. Yes b. No b) Is the horse exhibiting asymmetrical weakness and focal muscle atrophy? a. Yes b. No c) What is the immune status of the horse? a. High-stress, performance, travel, weaning, etc. b. Presence of metabolic, endocrine and/or other chronic infectious diseases c. Age-related immunosenescence d. Normal Navigating the Diagnostic Challenges of EPM Nicola Pusterla, DVM, PhD, DACVIM, DAVDC-Equine is a professor of equine internal medicine and dentistry at the University of California, Davis, School of Veterinary Medicine. His research focus is on equine infectious diseases with an emphasis on molecular epidemiology. Dr. Pusterla also leads the UC Davis Equine Infectious Disease Research Laboratory. by Nicola Pusterla, DVM, PhD, DACVIM Critical Case Question: Aer you've conducted a thorough physical and neurological exam, where does EPM sit on your list of differentials? HINT: If asymmetric gait and focal muscle atrophy are present, EPM should be considered a top differential.

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