Practical NeurologyUpdates to the McDonald Diagnostic Criteria for Multiple Sclerosis

Updated diagnostic criteria expand anatomic locations, incorporate new biomarkers, and allow MS diagnosis without mandatory dissemination in time demonstration.

🔬 Clinical Considerations

• Optic nerve added as a 5th DIS location, requiring orbital MRI, OCT intereye difference ≥6 μm, or delayed VEP latencies to confirm involvement
• DIT is no longer mandatory; extent of spatial involvement plus CSF biomarkers or MRI markers can establish diagnosis in qualifying cases
• Kappa free light chain now interchangeable with oligoclonal bands for DIT substitution, offering faster, automated, rater-independent results with comparable accuracy
• CVS and paramagnetic rim lesions add specificity: Select-6 CVS achieves 90% sensitivity/89% specificity; ≥4 PRLs signal greater neurologic disability risk
• Patients aged ≥50 or with vascular comorbidities require additional confirmatory features (classical spinal cord lesion, positive CSF, or Select-6) to reduce misdiagnosis

🎯 Practice Applications

• Order orbital MRI and OCT when optic neuritis is suspected to satisfy the new optic nerve DIS criterion
• Request CSF KFLC testing as a practical alternative when OCB testing faces turnaround or access limitations
• Apply Select-6 CVS criteria on susceptibility-weighted sequences for patients with vascular risk factors or age ≥50
• Reassess existing CIS and RIS diagnoses against 2024 criteria: some patients may now qualify for formal MS diagnosis without new clinical events

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