EPM Myths
To steal a line from Winston Churchill, equine protozoal myeloencephalitis (EPM) is a riddle, wrapped in a mystery, inside an enigma. It's a frustrating disease from many standpoints, and myths abound. A recent article from TheHorse.com highlights some of these myths.
One of the biggest problems with EPM is diagnosis. In Ontario, a large number of horses are "diagnosed" with EPM, but very few actually have the disease. Probably hundreds of horses (particularly race horses) are treated for every single horse that actually has EPM. Many horses get treated without any diagnostic testing at all, but merely based on vague (or no) signs that could be caused by numerous other conditions.
A key point in the article is the need for diagnostic testing and a reasonable suspicion of EPM before considering the diagnosis (and treatment). Unfortunately, none of the tests we have available are very good by themselves, which complicates matters. When you have a marginal quality test and you use it in horses that probably don't have disease, you end up with a lot of false positive results, which often results in unnecessary treatment.
According to experts in this article (with whom I absolutely agree), EPM should only be diagnosed if:
- The horse has clinical signs consistent with the disease (this does not include vague, non-neurological signs like not running as fast as the trainer or owner wants)
AND
- A veterinarian has ruled out all other neurologic diseases that are similar to EPM
AND
- You have a positive EPM test result.
There are several testing options, each with good and bad points. There's not currently one "right" test that everyone should use. They key is SOME test should be used and it MUST be used in conjunction with a proper examination and other testing to rule out diseases like Wobbler's syndrome. Only when you are left with no other diagnoses and a positive EPM test should you really consider EPM likely.
There's a good statement at end of the article: "If it looks like EPM and smells like EPM ... it probably isn't. EPM remains a rare cause of neurologic disease in horses." EPM certainly does exist and can be a serious disease, but make sure you are not wasting time, effort and money treating a horse that doesn't really have it.
