Fig. 1.

2017 McDonald criteria for demonstration of DIS and DIT in patients with a CIS suggestive of MS. Typical MRI examples (orange arrowheads) of (a) periventricular, (b) cortical/juxtacortical, (c) infratentorial and (d) spinal cord MS lesions. DIS can be demonstrated by ≥1 T₂-hyperintense lesions in ≥2 of 4 typical areas of the central nervous system (i.e., periventricular, cortical/juxtacortical, infratentorial or spinal cord). DIT can be demonstrated by (e) a simultaneous presence of Gd-enhancing (orange arrowhead) and non-enhancing (white arrowheads) lesions at any time; (f) a new T₂-hyperintense and/or Gd-enhancing lesion on follow-up MRI (orange arrowheads), with reference to a baseline scan, irrespective of the timing of the baseline MRI. For the definition of both DIS and DIT, the distinction between symptomatic and asymptomatic lesions has been removed in the 2017 revision of the McDonald criteria. (g) In patients with a typical CIS suggestive of MS fulfilling DIS criteria and with no better explanation for the clinical presentation, the demonstration of CSF-specific OCBs, i.e., not present in the serum but only in the CSF, substitutes for the requirement of fulfilling DIT, thus allowing a diagnosis of MS, even if the clinical and MRI findings do not meet the criteria for DIT. Abbreviations: CIS, clinically isolated syndrome; CSF, cerebrospinal fluid; DIS, dissemination in space; DIT, dissemination in time; Gd, gadolinium; MRI, magnetic resonance imaging; MS, multiple sclerosis.