The 2024 McDonald criteria for the diagnosis of multiple sclerosis: implications for clinical practice.

The 2024 revisions to the McDonald criteria mark a major shift in the diagnosis of multiple sclerosis (MS), reflecting advances in imaging and biomarker science. The updated framework adopts a more biologically anchored approach, integrating radiological and cerebrospinal fluid evidence to enable earlier and more accurate diagnosis. Key changes include recognition of the optic nerve as a fifth anatomical site for dissemination in space, incorporation of advanced MR imaging markers such as the central vein sign and paramagnetic rim lesions to improve specificity, and acceptance of the kappa free light chain index as a quantitative alternative to oligoclonal bands. In selected patients with highly characteristic clinical and imaging features, MS may now be diagnosed without demonstration of dissemination in time, reducing diagnostic delay. A unified pathway across relapsing and progressive phenotypes, including children, promotes consistency, while defined pathways also allow diagnosis in certain asymptomatic individuals, including those with radiologically isolated syndrome, when supported by biomarkers. Implementation will require access to advanced imaging, standardised laboratory testing, multidisciplinary expertise and careful clinical judgement to minimise misdiagnosis and ensure equitable access.