[Can multiple sclerosis be diagnosed on a first demyelinating event?]

Progression is required. The definition of multiple sclerosis (MS) relies on the notion of temporo-spatial dissemination of inflammatory demyelinating neurological episodes. Until recently, in order to retain the diagnosis of definite MS, two successive neurological episodes had to be observed in two different territories. Since the commercialisation of new immunomodulating treatments, and in particular the recent demonstration of their efficacy in delaying the onset of a second neurological episode, it has been necessary to draw-up new criteria. New criteria have recently been proposed by a group of experts and they emphasize the fundamental role played by magnetic resonance imaging. New priorities. With these new criteria, certain aspects have become front-line. This is the case of the necessity of foreseeing more exhaustive differential diagnoses of MS, so as to avoid the erroneous initiation of a specific treatment. There is also the problem of the selection of patients at high risk of a potentially progressive MS, not all patients necessarily require such treatment at the start. Updating. We successively present the recently revised diagnostic criteria in order to be able to diagnose MS after the first demyelinising episode, we then study the clinical and paraclinical predictive elements that provide supplementary support for MS and, notably, progressive MS. We also discuss the differential diagnoses to be excluded according to the clinical context and, lastly, we will attempt to assess the practical consequences of an early diagnosis, not only with regard to its announcement, but also with regard to the therapeutic decisions to be made.