Old dog-new tricks - Suspected MUO in two Australian shepherd dogs : a case series

Meningoencephalitis of unknown origin (MUO) is mostly considered a
disease of small and terrier breeds aged between approximately three
and seven years, with a recent study stating that 25% of MUO cases
affect large breeds, with no Australian Shepherds listed until now. In
this case study, 2 Australian Shepherds, 10 and 11 years old, were
presented with progressive clinical signs of multifocal encephalopathy.
Magnetic resonance imaging (MRI) revealed multifocal, intraaxial
lesions of the cerebral cortical grey matter in one dog and cerebellar
and thalamic grey matter in the other dog respectively. Lesions were
hyperintense in T2W and fluid-attenuated inversion recovery
sequence with no to mild inhomogeneous contrast enhancement. A
diagnosis of MUO was based on diagnostic imaging, cerebrospinal
fluid findings, negative regional infectious titres and good response to
immunomodulatory therapy. Both dogs had serial MRIs. Follow-up
MRI examination after 3 months showed complete resolution of MRI
abnormalities in one dog treated with cytarabine and prednisolone.
The other dog showed recurrence of clinical signs 23 months after
diagnosis and tapering of prednisolone. Re-MRI showed multifocal de
novo lesions. After start of cytarabine and prednisolone treatment,
clinical signs improved again. The dog is still alive at the time of writing,
the other was lost to follow up 5 months after the diagnosis. In
conclusion, MUO should be on the differential list also in elderly
patients, which can have good outcomes with immunomodulatory
therapy. Further studies are needed to explore if Australian Shepherds
are at an increased risk of MUOs at senior age.