The 2024 update to the McDonald criteria for multiple sclerosis aims to be more inclusive, covering paediatric and elderly patients, as well as those with atypical symptoms or comorbidities. These criteria emphasise objective evidence of central nervous system involvement through clinical signs and biomarkers from fluid analysis or imaging. Several new biomarkers have been added, although some are not yet widely accessible but are expected to be implemented soon: kappa-free light chains in cerebrospinal fluid, which are more reproducible and cost-effective than oligoclonal bands, along with advanced imaging techniques such as the central vein sign and paramagnetic rim lesions on susceptibility-weighted imaging. Cases with incidental magnetic resonance imaging hyperintensities, identified as radiologically isolated syndrome (RIS), may also be classified as preclinical MS if they show T2 lesions in at least two typical locations and meet other specific biomarker criteria. Careful, step-by-step evaluation is essential to prevent misdiagnosis, especially in paediatric and late-onset MS, and in cases with comorbidities. The inclusion of RIS individuals or those with atypical presentations marks a crucial shift in the MS spectrum, requiring expertise and the use of specific biomarkers.