Comparison of the Performance of the 2024 and 2017 McDonald Criteria for the Diagnosis of Multiple Sclerosis in Real Life

The new diagnostic criteria for multiple sclerosis (MS) were published in October 2025 (Montalban et al. 2025). They introduce significant changes compared to the previous criteria from 2017: inclusion of previously "borderline" forms and use of new imaging techniques, inclusion of ophthalmological data, and a new cerebrospinal fluid (CSF) test: the kappa index. It is important to document whether these 2024 criteria, when applied in real life, will enable the diagnosis of patients who would not have been diagnosed using the previous criteria. Furthermore, the threshold to be used for the kappa index in relation to the reference test (IgG oligoclonal bands Obs in CSF) is insufficiently documented. Primary objective: to compare the percentage of patients diagnosed with MS following initial neurological assessment according to the 2024 McDonald criteria and the previous 2017 version. Secondary objectives: compare the percentage of patients receiving the diagnosis according to the two versions; document the need for the new tests appearing in the 2024 criteria; determine the optimal threshold for the kappa index. Methodology: all patients consulting in the neurology department of the Nancy and Metz hospitals between September 1, 2025, and December 31, 2026, followed for two years. No additional tests beyond those required for routine care. The 2017 version of the diagnostic criteria does not require any other tests. The diagnosis according to the 2017 criteria can therefore be reconstructed for each patient. At the end of the initial assessment, the percentage of patients diagnosed according to the two versions is compared, and this comparison will be repeated at different points in time over a two-year period. The contribution of each test will be evaluated using standard diagnostic performance markers, and the relevant kappa index threshold for reaching a diagnosis will be evaluated in relation to the presence of IgG OBs (gold standard). The expected outcomes are the use of the most useful tests to achieve early diagnosis without complicating management, and to estimate which tests are not relevant for diagnosis in order to enrich the knowledge that will enable future revision of these criteria.