Equine Protozoal Myeloencephalitis (EPM) Testing

WHY TEST?  EPM is a neurological disease of the Americas. It is most commonly caused by the parasite Sarcocystis neurona and more rarely by Neospora hughesi.  The standard of practice for diagnosis is to perform a complete neurological exam, accompanied by laboratory tests that detect an immunological response to infection.  Testing of cerebrospinal fluid (CSF), with a paired serum, is more predictive of active disease than serum alone.  The reluctance to perform a spinal tap due to risk, cost or inexperience is understandable and although not the preferred approach, a positive serum IgG test in the presence of neurologic signs and history compatible with EPM, supports a diagnosis of EPM.  Although response to treatment is often used as a diagnostic test, there are many false results that would have been predicted by prior serum and CSF testing.  Testing of non-neurologic horses is generally not recommended.  Repeat side-by-side testing with any quantitative test format can be useful in noting changes in the level of IgG with time, either due to natural response or in response to treatment.