To evaluate whether the analysis of the central vein sign (CVS)  and the  “50% rule” can identify subgroups of multiple sclerosis (MS) patients.

 Definite MS patients (diagnosed according to McDonald criteria) and MS patients  with clinical laboratory and MRi markers of better explanation, but not fulfilling the diagnostic criteria of other diseases (MS-plus), were included. The patients  received one MRi scan including one FLAIR and one T2* sequence, and were statyfied according to the 50% rule. The clinical course of the two patient cohorts was then evaluated.

The median CVS frequency of the definite MS patients (n= 30) and of the MS-plus patients  (n= 55) was 91% (range, 68-100%) and 55% (range 11-95%) respectively. Out of the MS-plus patients, 28 met the “50% rule”, showing a median frequency of 22% (range 11-40%), whereas the other 27 MS-plus had a CVS frequency within the range of the definite MS. No other MRi parameter segregated with each group. Analysis of the natural history of the disease, currently suggests a more benign disease course in the MS-plus patiens fulfilling the 50% rule with respect to those who don’t.

A group of MS-plus patients with low CVS frequency (fulfilling the 50% rule) can be identified by one conventional MRi scan. The natural history of the disease in this group seems more benign than in definite MS and in MS-plus not fulfilling the 50% rule, suggesting either that these patients have  a benign MS form or that are not MS.