The clinical presentation of MUO may be acute or chronic and reflect focal or multifocal disease. Clinical signs reflect the location of the lesion(s). For example, dogs with forebrain disease may show signs of compulsive circling, seizures, behavior changes, or blindness. Dogs with brainstem disease often show vestibular signs, but other cranial nerves may also be affected.
Small dog breeds are more commonly affected, which suggests a genetic predisposition.2,3 Recently, genetic markers were identified in pug and Maltese dogs, which indicates a genetic risk for the development of MUO in those breeds.2,3 Although small dog breeds are overrepresented, MUO has been diagnosed in large dog breeds as well.4
Common magnetic resonance imaging (MRI) abnormalities include multifocal hyperintensity on T2-weighted and fluid-attenuated inversion recovery (FLAIR) imaging with variable contrast enhancement. MRI is normal in some cases, however.1 Supportive cerebrospinal fluid (CSF) findings include mixed mononuclear pleocytosis with increased protein concentration. Both total nucleated cell count (TNCC) and protein concentration may be normal in some dogs.5 Biopsy may be pursued in some cases to obtain a histopathologic diagnosis.
Granger and Smith proposed the following criteria for a clinical diagnosis of MUO1:
- Multifocal neuroanatomic lesion localization
- Age >6 months
- Intra-axial hyperintense lesions on T2-weighted MRI
- Pleocytosis with >50% mononuclear cells and increased protein concentration in CSF
- Negative testing for geographic-specific infectious diseases1
Related Article: Progressive Behavioral Changes in a Dog