North American Veterinary Licensing Examination (NAVLE) Practice Test

Equine protozoal myeloencephalitis (EPM) is a central nervous system disease caused by the protozoan parasite Sarcocystis neurona. This condition is characterized by a variety of neurological signs, which can include muscle atrophy due to disuse or neurological impairment.

In the case of EPM, the horse may display asymmetrical muscle atrophy, particularly in the left shoulder and right hindquarter, as a result of neurological dysfunction. The impairment affects the nerve signals that control muscle movement, leading to weakness and muscle wasting. As the horse is unable to use these muscles effectively, atrophy occurs due to the lack of stimulation and exercise.

Understanding how EPM impacts the nervous system of the horse helps explain the particular pattern of muscle atrophy observed. The left shoulder and right hindquarter are often affected due to the specific pathways involved in the central nervous system lesions caused by the parasite.

While conditions like sarcoidosis, neuropathy, and colic may present with other clinical signs, they do not specifically relate to the distinct muscle atrophy pattern associated with EPM. Therefore, equine protozoal myeloencephalitis is directly linked to the atrophy of the left shoulder and right hind