EPM in a Horse

A middle-aged Quarterhorse gelding presented for a history of strange gait and apparent pelvic limb weakness. The clinical signs developed suddenly over 24 hours. The gelding was current on vaccination for West Nile virus, Eastern Equine Encephalitis, and rabies. Neurologic exam noted a gelding in good body condition, alert, responsive yet quite "wobbly" in the hind limbs. Closer examination of all 4 limbs revealed severe weakness in both hind limbs. The degree of weakness was significant enough that the horse was having difficulty remaining standing. Importantly, the hind limb weakness was NOT symmetrical but was more severe in the left hind limb compared to the right hind limb. In the video below, the gelding is bearing most of his weight on the forelimbs and the result is a tendency to spin on the hind limbs due to the severe weakness of the pelvic limbs. 

Based on the neurologic exam, the most likely disease processes affecting this horse include Equine Protozoal Myeloencephalitis (EPM), spinal cord trauma, Eastern Equine Encephalitis (EEE), and West Nile Encephalitis. The sudden or acute onset of clinical signs is most consistent with spinal cord trauma however there was no history of a traumatic event and there were no external signs of such. Equine Protozoal Myeloencephalitis typically does not develop such severe signs over night however such clinical history is possible. The likelihood of either EEE or West Nile virus encephalitis is low in a well vaccinated horse yet not impossible! Diagnosis of encephalitis is dependent on serum testing and confirmation of EPM is dependent on testing of cerebral spinal fluid (CSF). Cerebral spinal fluid can be collected from two location including the atlanto-occipital (AO) joint space and the lumbo-sacral (LS) joint space. It was determined to collect CSF from the LS region. This option was chosen since it would be performed in the standing horse with moderate sedation. Collecting CSF from the AO site typically requires short term anesthesia and the ability of this horse to rise from recumbency was questioned. CSF fluid was collected and submitted for testing. The sample was positive and EPM was confirmed as the disease process in this horse. He is currently being treated with a variety of medications/supplements and the client is committed to treating for 4-6 months.

Read more about EPM @

http://www.aaep.org/health_articles_view.php?id=248