Diagnosis of Multiple Sclerosis

OBJECTIVE: This article describes the features and application of the 2024 McDonald criteria for the diagnosis of multiple sclerosis (MS). LATEST DEVELOPMENTS: The updated 2024 McDonald criteria are designed to be inclusive, with multiple new pathways to diagnosis that are applicable across the age spectrum and for patients with typical, nonspecific, or incidental presentations. New fluid and MRI biomarkers have been incorporated, including the kappa free light chain index, the central vein sign, and paramagnetic rim lesions. Anatomic regions for the fulfillment of dissemination in space now include the optic nerve as a fifth location, incorporating evidence of an optic nerve lesion demonstrated by either MRI, optical coherence tomography, or visual evoked potentials. ESSENTIAL POINTS: The 2024 McDonald criteria strongly recommend the confirmation of objective evidence of central nervous system involvement by imaging in addition to clinical findings, while additional biomarkers may be needed in specific instances. However, if these paraclinical tools are unavailable, a pragmatic approach incorporating clinical findings is permitted. MS diagnosis requires careful neurologic evaluation and expertise for the interpretation of paraclinical findings; the accurate performance of the diagnostic criteria still relies on the clinician's knowledge of typical clinical presentations and MRI findings of MS and the recognition of red flags suggesting alternative diagnoses. The revised criteria can be applied at all ages and for asymptomatic individuals; however, caution is required to avoid misdiagnosis, particularly for pediatric, older-onset, and asymptomatic presentations.