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Background: Evidence suggests that Epstein-Barr virus (EBV) plays a role in triggering or perpet-

Background: The McDonald criteria include MRI evidence for dissemination in space and dissemination in time for the diagnosis of multiple sclerosis in young adult patients who present with clinically isolated syndromes (CIS) typical of the disease. Although a major advance, the criteria have limited sensitivity for making an early diagnosis. Objective: To compare the performance of McDonald criteria and modified McDonald criteria for dissemination in space and time for assessing the development of clinically definite multiple sclerosis. Methods: McDonald criteria were modified using the combination of a less stringent definition for dissemination in space and allowing a new T2 lesion per se after three months as evidence for dissemination in time. Modified and McDonald criteria were applied in 90 CIS patients at baseline and at three month follow up scans. Results: Both criteria were highly specific (.90%) but the modified criteria were more sensitive (77% v 46%) and more accurate (86% v 73%).Conclusions: These modified criteria should be evaluated in other CIS cohorts.A n essential requirement in making the diagnosis of multiple sclerosis is that there should be objective evidence for central nervous system (CNS) white matter lesions disseminated in both space and time. Past criteria relied mainly on clinical evidence for dissemination in space and time.1 However, in 2001 new (McDonald) criteria were published that allowed MRI evidence for dissemination in space and time in the diagnosis of multiple sclerosis in patients who experienced a single acute clinical episode considered characteristic of the disease (known as a clinically isolated syndrome (CIS)).2 While the McDonald criteria have high specificity for the subsequent development of clinically definite multiple sclerosis (CDMS) when applied in CIS cohorts followed prospectively, 3 4 they have several limitations.5 6 Notably, the complex magnetic resonance imaging (MRI) criteria for dissemination in space 7 8 (table 1) have been considered too stringent, and the dissemination in time criterion of a new gadolinium enhancing lesion after three months has limited sensitivity in making an early diagnosis. The dissemination in space criteria also include gadolinium enhancement, which-strictly speaking-is a feature of lesion activity rather than location.An early and accurate diagnosis of multiple sclerosis is increasingly important for counselling individual patients and potentially for making decisions on the use of disease modifying treatments. We were therefore interested in whether the MRI criteria for dissemination in space and dissemination in time could be modified so that they improve the accuracy of early diagnosis. In this report we describe the findings using the combination of a less stringent definition for dissemination in space and allowing a new T2 lesion per se after three months as evidence for dissemination in time. METHODS Rationale for modified criteria Dissemination in spaceThe MRI criteria for dissemination in space were modified with th...