MS, MRI, and the 2010 McDonald criteria: a Canadian expert commentary

Since the first development of diagnostic criteria for multiple sclerosis (MS), there have been regular revisions of disease definitions and diagnostic thresholds aimed at improving specificity while maintaining sensitivity. The central requirements for diagnosis of MS are dissemination in space (DIS) and dissemination in time (DIT) of lesions in the CNS, with the proviso that there should be no alternate diagnosis that better explains the clinical presentation. The most definitive diagnosis is the purely clinical one, with 2 separate attacks of symptoms (fulfilling DIT criteria) involving at least 2 different areas of the CNS (fulfilling DIS criteria). In patients who have had a first but not a second clinical attack, the McDonald criteria provide guidance on how paraclinical evidence can be used to support a diagnosis of MS. Recently, the McDonald criteria were revised and new definitions for DIS and DIT proposed. In response to that revision, a panel of Canadian MS neurologists and one neuroradiologist created this commentary regarding the clinical implications and applications of the 2010 McDonald criteria.