The clinical course of acute disseminated encephalomyelitis

The objective of this review is to describe recent advances in understanding the clinical course of pediatric and adult acute disseminated encephalomyelitis (ADEM), especially the risk of relapse and conversion to multiple sclerosis (MS). The diagnosis of ADEM is reached on clinical grounds, typically in the setting of a post-infectious meningoencephalitic syndrome associated with multifocal neurological symptoms and signs, magnetic resonance imaging (MRI) evidence of white matter lesions and exclusion of other causes. Although typically monophasic, several case series demonstrate 'multiphasic' or 'recurrent' forms of ADEM with clinical relapses occurring within a short interval of disease onset. Furthermore, the estimated risk of developing MS is substantial for both children (0-33%) and adults (~35%). Advances in neuroimaging have identified some MRI features that have predictive value for a relapsing course but they are not accurate enough for therapeutic decision-making; a diagnosis of monophasic ADEM should be made with caution in all cases, especially those presenting in adulthood. Research in ADEM and related disorders remains hampered by lack of prospective studies, specific and reproducible clinical case definitions and variable follow-up methods. Standardization of these variables would facilitate identification of more accurate diagnostic and prognostic variables, discovery and testing of potential objective biomarkers that would, in turn, allow early prediction of a relapsing course and appropriate therapeutic interventions.