The aim is to analyze all files centralized as Radiologically Isolated Syndrome (RIS) and collect clinical, biological, and imaging data to promote research.

Since the first published 2009 RIS diagnostic criteria, our consortium has collected cases with incidental findings on the brain or spinal cord MRI suggestive of demyelinating disease without Multiple Sclerosis (MS) signs and symptoms.

We collected prospectively all cases addressed for suspicion of RIS in 35 MS clinics, and a double-blind MRI reading agrees for RIS status on imaging and patient medical history. These cases are classified into three groups: (1) 2009 RIS subjects fulfilling at least three out of four criteria for Dissemination in Space (DIS); (2) Suspected-RIS subjects fulfilling only one or two criteria for DIS (PRERIS); (3) NON-RIS.

This cohort contains 617 files in October 2021: 452 (75%) Women, Mean age at inclusion 38 years [10 -71]. On the 467 confirmed RIS cases: during the mean follow-up of 15.4 months [0-203], 103 (22%) have converted clinically. Meantime for the seminal event: 40.8 months [1.5 – 196.9] after the index MRI.

On the 150 PRERIS cases: during the mean follow-up of 35.3 months [0.1-180], 26 (17.3%) have converted clinically. Meantime for the seminal event was 54.1 months [3.2-233] after the index MRI.

Of the 124 PRERIS (82.7%) who have not converted clinically, 58 (46.8%) have MRI DIT and eventually fulfilled the 2009 RIS criteria, and 66 (53.2%) are still classified as PRERIS.

Fifty-nine cases were classified after adjudication as NON-RIS for either suggestive history of demyelinating disease (9), abnormalities suggestive of another condition (12), or non-specific lesions (38).

This cohort demonstrates that 1/ Some RIS subjects can rapidly present clinical event 2/PRERIS subjects can evolve either to 2009 RIS or to MS 3/ Misdiagnosis is possible, and criteria sensibility should not overrule specificity.