Studio RM dell'encefalomielite acuta disseminata

Abstract

Parole chiave: encefalomielite acuta disseminata, RM RIASSUNTO-L'encefalomielite acuta disseminata e una patologia infiammatoria demielinizzante a carattere diffuso o multifocale, che colpisce la sostanza bianca dell'encefalo e/o del midollo spinale.Insorge a distanza di tempo variabile (2 settimane-5 mesi) da eventi infettivi ad eziologia virale, oppure da pratiche vacciniche. Il decorso, acuto e monofasico, ha una durata di 1-3 settimane. Tale malattia, che ha un'incidenza sicuramente superiore rispetto a quanto riportato nelle statistiche, colpisce prevalentemente l'infanzia e l'adolescenza.Dal punto di vista istopatologico, la malattia e caratterizzata dalla presenza di infiltrati infiammatori perivascolari, soprattutto perivenulari, di cellule mononucleate, associati a zone di demielinizzazione che seguono il decorso delle venule. La gliosi astrocitaria e il risultato riparativo.La somiglianza clinica fra encefalite acuta disseminata e sclerosi multipla, e quindi l'encefalite allergica sperimentale, ha fatto prospettare nella sua patogenesi l'intervento di meccanismi autoimmunitari. Dal punto di vista neuroradiologico, le lesioni ascrivibili ad encefalite acuta disseminata non presentano un'espressivita unitaria, anche se e possibile individuare alcuni caratteri relativamente costanti.Tale stato di cose, innanzitutto mette in dubbio la possibilita di una diagnosi solamente neuroradiologica di encefalite acuta disseminata, che invece per essere posta necessita di un accurato controllo cliniconeuroradiologico, ed in seconda istanza alimenta la domanda «ci troviamo di fronte ad un'entita nosografica ben distinta oppure ad uno spettro di malattie?».SUMMARY -Acute disseminated encephalomyelitis is a diffuse or multifocal demyelinating disorder affecting the white matter of the brain and/or spinal cord and may arise some time (2 weeks-5 months) after viral infections or immunisation. The disease has an acute course lasting 1 to 3 weeks and mainly affects children and adolescents with a far more frequent incidence than that listed in statistical reports.Histopathology reveals perivenous, especially perivenular, inflammatory exudate and mononuclear cells associated with small foci of demyelination with a perivenular distribution. Astrocytic gliosis is the the outcome of repair. The clinical similarities between acute disseminated encephalomyelitis and multiple sclerosis and hence experimental allergic encephalitis have implicated auto immune mechanisms in the pathogenesis of the disorder.The neuroradiological features of acute disseminated encephalomyelitis are not diagnostic, but some relatively constant changes are displayed in MR scans. Thorough clinical and neuroradiological follow-up is required to establish diagnosis and the disorder must be distinguished from a spectrum of different diseases.

Acute Disseminated Encephalomyelitis

“…Among the neuroimaging findings, CT scan may be negative in at least one third of the cases, while MRI usually shows lesions of greatly varying number, hyperintense in T2-weighted sequences and normal or hypointense in T1-weighted sequences 5,7,15 . They are often bilateral, relatively symmetrical with indistinct outlines due to the surrounding oedema, but show little or no mass effect 5 .…”

“…Neuropathological findings show white matter mostly damaged with infiltration of perivascular monocytes, areas of demyelination with gliosis but without axonal involvement 5,34 .…”

“…Differential diagnosis can be made with many other pathologies like Lyme's disease, subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy, blood coagulation diseases, vasculitides, metabolic leukodystrophies, mitochondrial diseases and haematological disorders 5 .…”

“…The course is usually characterised by a complete regression of the clinical symptoms and neurological lesions but often the clinical impairment is faster than neuroradiological deterioration 5,27 . Sometimes remaining neurological deficits (10-20%) and, rarely, death 2,23,34 are observed.…”

“…The areas mostly involved are the semioval centres, the cerebellum, the deep thalamic and basal structures and the spinal cord 5,11,29 .…”