Archive Case #15: Equine Protozoal Myeloencephalitis

Clinical Clues

1. A 9-year-old Quarter Horse gelding is evaluated for a gradually worsening gait abnormality.
2. The owner reports intermittent stumbling and poor performance over several weeks.
3. Asymmetric muscle loss becomes noticeable over the right hindquarter.
4. Neurological examination reveals asymmetric, multifocal deficits affecting multiple limbs.
5. Cervical imaging is unremarkable, but CSF testing supports intrathecal antibody production against Sarcocystis neurona.
6. A protozoal infection of the equine central nervous system associated with opossum-contaminated feed commonly causes this pattern.

Diagnosis

Equine Protozoal Myeloencephalitis

This case is most consistent with Equine Protozoal Myeloencephalitis because of the progressive asymmetric ataxia, focal muscle atrophy, and supportive CSF findings for Sarcocystis neurona. The most important clues are the multifocal neurologic deficits, asymmetry, and negative cervical imaging, which make a compressive cervical lesion less likely.

Educational Use

Vetdle archive cases are educational veterinary games for diagnostic reasoning practice. They do not provide veterinary advice, diagnosis, treatment, or professional medical guidance.