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2 year old female spayed mixed breed dog. Presented for a two week history of progressive neurologic signs including ataxia and circling to the left. The patient has a longer, 8 month history of skin disease which has been treated with antibiotic and prednisone therapy.

Clinical findings: On admission, patient was quiet and alert. Severe alopecia and dermatitis was present over her head, abdomen, and legs. On neurologic examination, rotary nystagmus noted, and circling to the left. Normal proprioception and postural reactions. Skin scrapings revealed severe demodex mite infestation, as well as pyoderma.

T2w transverse

T2-FLAIR (left), GRE (right)

T1w pre (left) and post-contrast (right)


Multiple T2 hyperintense lesions are seen through the brain. The right and left caudate nuclei are hyperintense on T2 images and mild to moderately contrast enhance. The right caudate nucleus is mildly enlarged and causing mild dorsomedial deviation of the lateral ventral wall of the right lateral ventricle. A poorly defined region of T2 hyperintensity is present in the cerebral cortex of the right temporal lobe, lateral to the caudoventral aspect of the right lateral ventricle. This region does not contrast enhance. A large oval to oblong region of poorly defined T2 hyperintensity is present occupying a large portion of the medulla oblongata. This region extends mildly caudal into the cranial spinal cord, through the level of cranial C1. On T2 images the cerebellum is diffusely mildly hyperintense. Contrast enhancement is present in the left cerebellar hemisphere cortex and cerebellar vermis.

Multifocal cerebral, midbrain and cerebellar disease.
Inflammatory/infectious differentials were thought most likely: infectious encephalitis (such as protozoal or fungal), and less likely necrotizing or granulomatous meningoencephalitis.


CSF analysis:
Mixed neutrophilic and macrophagic pleocytosis (inflammation) with protozoal infection; the protozoal organisms were most suggestive of Sarcocystis spp.

Outcome: Patient deteriorated rapidly despite treatment and owners elected euthanasia.

Necropsy and PCR results:
Brain: Severe necrotizing lymphohistiocytic meningoencephalitis
Spleen and lymph nodes: Moderate lymphoid depletion
Haired skin: Severe pyogranulomatous folliculitis/perifolliculitis with numerous intralesional Demodex spp. mites
PCR negative for Toxoplasma sp and Neospora sp. PCR positive for Sarcocystis neurona

S. neurona is an intracellular protozoal organism which more commonly affects the central nervous system of horses. The opossum is the definitive host and aberrant or intermediate hosts include horses, sea otters, armadillos, and cats. In these intermediate hosts, only asexual stages are found and lesions are usually confined to the central nervous system.

Based on the history of glucocorticoid steroid use, histologic evidence of lymphoid depletion, and fulminant demodectic mange, this animal was likely immunosuppressed which may have played a role in the central nervous system disease in this patient.


  1. Dubey JP, Chapman JL, Rosenthal BM, et al. Clinical Sarcocystis neurona, Sarcocystis canis, Toxoplasma gondii, and Neospora cancium infections in dogs. Vet Parasit 2006; 137:36-49.
  2. Sykes JE, Dubey JP, Lindsay LL, et al. Severe Myositis Associated with Sarcocystis spp. Infection in 2 dogs. J Vet Intern Med 2011;25:1277-1283.
  3. Cooley AJ, Barr B, Rejmanek D. Sarcocystis neurona Encephalitis in a Dog. Vet Pathol 2007;44:956-961.