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The recommended diagnostic work-up of MUO is the same as for SRMA. However, MRI plays a signi cant role in MUO cases, which usually have multifocal or diffuse hyperintense lesions on T2-weighted images (WI) and  uid-attenuated inversion recovery (FLAIR), and possible contrast enhancement on T1-WI. The suspicion of in ammatory MUO is con rmed by CSF analysis, which reveals mild to moderate pleocytosis, typically dominated by mononuclear cells, but may also consist of mixed cells, and increased amounts of protein.
The treatment for MUO remains immunosuppression, usually involving corticosteroids, which are often administered at higher dosages than for SRMA.
The recommended protocol, given infectious causes have been ruled out, includes7:
• 1.5 mg/kg BID for 3 weeks
• 1.0 mg/kg BID for 6 weeks
• 0.5 mg/kg BID for 3 weeks
• 0.5 mg/kg SID for 3 weeks
• 0.5 mg/kg every other day, possibly reduced
Adjunctive immunosuppression therapy with e.g. cytosine arabinoside, cyclosporine, procarbazine or lomustine may be useful, if prednisolone is insuf cient, or if the side effects are intolerable.
In general, the prognosis with MUO is considered less favourable than with SRMA, and many dogs die within the  rst couple of months8. The prognosis may to some extent depend on the localisation of the lesion, as forebrain lesions presumably have a better prognosis than brain stem lesions9. Furthermore, dogs with focal disease rather than multifocal disease have a better chance of survival9.
1. Coates JR & Jeffery ND. Perspectives on meningoencephalomyelitis of unknown origin. Vet Clin Small Anim 2014;44:1157-1185
2. Tipold A & Schartzberg SJ. An update on steroid responsive meningitis- arteritis. Journal of Small Animal Practice 2010;51:150-154
3. rd edn, WB Saunders, Elsevier Science
4. Tipold A & Jaggy A. Steroid responsive meningitis-arteritis in dogs: long-term study of 32 cases. Journal of Small animal Practice 1994;35:311-316
5. Lowrie M, Penderis J, McLaughlin M, Eckersall PD, Anderson TJ. Steroid responsive meningitis-arteritis: a prospective study of potential disease markers, prednisolone treatment, and long-term outcome in 20 dogs (2006-2008). Journal of Veterinary Internal Medicine 2009;23:862-70.
6. Vestergaard TN, Kjelgaard-Hansen M, Berendt M, Gredal H. Systemic
in ammatory activity is frequently absent in dogs with acute in ammatory CNS
disease. Poster at 13 EVECCS Meeting, Copenhagen, June 2013
7. Talarico LR & Schatzberg SJ. Idiopathic granulomatous and necrotising in ammatory disorders of the central nervous system: a review and future perspectives. Journal of Small Animal Practice 2010;51:138-149.
8. Lowrie M, Smith PM, Garosi L. Meningoencephalitis of unknown origin: investigation of prognostic factors and outcome using a standard treatment protocol. Veterinary Record 2013;172:527.
9. Muñana KR, Luttgen PJ. Prognostic factors for dogs with granulomatous meningoencephalomyelitis: 42 cases (1982-1996). Journal of the American Veterinary Medical Association 1998;212:1902-1906.
An Urban Experience
• Treatment can usually be stopped after 5-7 months, but depends on the individual course of disease
During treatment, dogs should receive regular check- ups every 4-6 weeks, and haematology and serum biochemistry performed in order to monitor possible signs of systemic in ammation and adverse reactions
in relation to prednisolone. If an increase in serum CRP was present as part of the initial clinical picture, this may also be a useful parameter to monitor in ammation and possible relapse5.
In most cases, the prognosis of SRMA is good, although relapses occasionally occur. It is important to stay in close contact with the owners during the entire treatment period and keep them informed of the side effects encountered with long-term prednisolone treatment.
As the clinical disease wanes off, side effects take over, e.g. polyuria, polydipsia, polyphagia, generalised muscle atrophy and weakness, hepatomegaly, a reduced level of physical activity and a dull and unhappy appearance. Especially, this ‘depressed behaviour’ is an enormous challenge to most owners, who should be informed that these signs are reversible.
On rare occasions, a CSF tap may be normal, despite
a classical clinical presentation of SRMA and a positive response to prednisolone. However, initiating treatment with prednisolone is not recommended, due to the many unwanted side effects seen with long-term prednisolone treatment, unless SRMA is highly suspected.
Meningoencephalitis of unknown origin (MUO)
As mentioned earlier, the term ‘Meningoencephalitis of unknown origin’ covers a syndrome of non-infectious CNS in ammatory diseases, which cannot be distinguished on clinical grounds alone. Accordingly, in the following MUO will be reviewed as a general clinical syndrome, rather than as speci c histopathological disease entities.
Although, MUO may affect any breed, toy and terrier breeds, pug dogs and Yorkshire terriers, seem to be overrepresented. Young dogs are predisposed, from 2-4 years of age, but dogs at all ages can get MUO1.
The clinical signs with MUO re ect the affected CNS region and hence vary from case to case. The disease usually has an acute onset, which progresses over
the following days. Clinical signs are often multifocal, depending of how widespread the in ammatory changes are, and may include seizures, depression, circling, vestibule-cerebellar signs and visual de cits. MUO may also involve the spinal cord, or even present as myelopathy alone. Signs of systemic in ammatory disease, e.g. pyrexia and leucocytosis, are less common than with SRMA7.

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