Differential diagnoses for seizures included infectious meningoencephalitis (eg, canine distemper virus [CDV] infection, neosporosis, toxoplasmosis, tick-borne disease [eg, Rocky Mountain spotted fever, ehrlichiosis], fungal infection [less likely]), noninfectious meningoencephalitis (eg, meningoencephalitis of unknown etiology), congenital anomalies (eg, hydrocephalus, porencephaly), hepatic encephalopathy secondary to portosystemic shunt, and toxin exposure.
CBC results showed a mild neutropenia (2,900/µL; normal, 3,300-10,100/µL), lymphopenia (500/µL; normal, 1,000-3,900/µL), and normocytic, hypochromic, nonregenerative anemia (hematocrit, 34.7%; normal, 41.7%-58.1%). Serum chemistry profile, urinalysis, and paired serum bile acid test results were unremarkable; thoracic radiographs appeared normal.
CDV real-time reverse transcription-PCR (RT-PCR) and serology (virus neutralization) results were positive (48; normal, <8). Although other infectious disease testing (eg, neospora and toxoplasma titers, tick-borne disease titers or PCR) could have been considered, CDV testing was the initial focus because of Poncho’s signalment, clinical history, concurrent neurologic and respiratory signs, and CBC findings.
Pending CDV results, brain MRI and CSF analysis were performed to evaluate for other structural causes of seizures. Brain MRI showed multifocal, asymmetric, intra-axial lesions in the left cerebrum and brainstem (Figure 1). Most likely differential diagnoses included infectious encephalopathies (eg, CDV infection) or meningoencephalitis of unknown etiology. CSF analysis was normal, and CSF distemper titer was negative (<1:4). Results likely reflected the acute stage of CDV encephalitis, during which CNS lesions are primarily characterized by direct viral replication and cellular injury leading to noninflammatory demyelinating lesions.1-3