MENINGOENCEPHALITIS OF UNKNOWN ORIGINS

The inflammatory diseases of the Central Nervous System are an extremely heterogeneous group of distinct diseases in meningitis, encephalitis, meningoencephalitis (ME) depending on whether meninges, brain parenchyma, or both are involved respectively.

They can be of an infectious nature or of unknown etiology, the latter forms include Granulomatous Meningoencephalitis (GME), Necrotizing Meningoencephalitis (NME) and Necrotising Leukoencephalitis (NLE), which differ from each other in topographical distribution of lesions and in breed specificity affected and, vice versa, they all share the absence of a known cause and the likely immune-mediated pathogenesis.

NME develops mainly in Pug, Maltese and Pinscher breeds and the lesions indistinctly affect white matter, gray matter and the meninges of the anterior brain; NLE, more frequent in Yorkshire breeds, causes alterations almost exclusively in the white matter of the forebrain and brainstem; finally, GME, typical of toy breeds, can be focal (single mass occupying space), disseminated (multiple lesions), ocular (involvement of chiasm and optic nerve).

It is not possible to make ante-mortem diagnoses of individual histopathological forms but only to elaborate a diagnostic suspicion on the basis of clinical data and those provided by diagnostic imaging techniques (CT, but above all magnetic resonance) and cephalorachidian CSF analysis.

The neurological deficits found vary according to the neuroanatomical region involved, the animal may have prosencephalic deficits (alterations in conscious proprioception, in the response to the threat, compulsive gait) or anomalies affecting the brain stem (cranial nerve deficit, ataxia, alterations of the sensory), etc.

The first-line of treatment is immunosuppression, taking into account the fact that it is assumed that EUTMs are pathologies induced by infectious phenomena that are quickly eliminated but responsible for the activation of an abnormal and destructive immune response.

The drug of choice is prednisone, used alone or in combination with other immunosuppressive agents, especially with Cytosine Arabinoside. During therapy, bone marrow function should be monitored by means of a blood count, since it can be suppressed by these drugs.

The prognosis is extremely variable and relapses are possible which must be faced with an aggressive and polypharmacological approach.