2024 McDonald Criteria: MRI and Paraclinical Updates for Multiple Sclerosis

A practical radiology review of 2024 McDonald Criteria: MRI and Paraclinical Updates for Multiple Sclerosis, focused on imaging findings, differential diagnosis, reporting points, and high-yield teaching pearls.

Definition

• 》Revised framework for diagnosing Multiple Sclerosis (MS) across all ages and clinical forms
• 》Emphasizes MRI and paraclinical biomarkers to increase specificity and allow earlier diagnosis
• Key Diagnostic Concepts
• DIS (Dissemination in Space): Lesions in ≥2 of 5 regions
• Periventricular
• Cortical/Juxtacortical
• Spinal cord
• Infratentorial

Optic nerve (NEW 5th region)

• Dissemination in time is not mandatory in every diagnostic pathway; the complete 2024 criteria and clinical context determine when it can be omitted.

Imaging Highlights

• Optic Nerve as 5th Location: Use MRI (fat-sat), OCT (RNFL ↓ ≥6 µm), or VEP (P100 latency ↑)
• Supports unilateral/bilateral optic neuritis or subclinical optic injury

Central Vein Sign (CVS)

• ≥6 lesions with central vein diagnostic specificity ↑↑

(Best with 3T or 7T MRI using T2/SWI)

• Helps differentiate MS from small vessel disease/migraine

Paramagnetic Rim Lesions (PRLs)

• Chronic active plaques with iron rim(Seen on susceptibility imaging)
• Presence of ≥1 PRL + DIS + DIT/CSF positivity diagnostic

CSF Biomarkers

Oligoclonal Bands (OCB) or Kappa Free Light Chains (kFLC) interchangeable

• The kFLC index is a quantitative alternative; interpret it using a validated laboratory method and threshold.

Paediatric MS

• Same unified criteria apply
• ≥50% lesions with CVS → strongly supports MS
• Test for MOG-IgG in <12 years to exclude MOGAD

Older Age & Comorbidities (≥50y)

• ↑ Misdiagnosis risk (migraine, SVD, autoimmune mimics)

Confirm with extra features

• CSF positivity
• CVS select-6 rule
• Spinal cord lesion

Radiologically Isolated Syndrome (RIS)

• Incidentally found T2 lesions with MS pattern
• If DIS + (DIT or CSF+ or CVS select-6) → can diagnose MS
• 50% convert to clinical MS in 10 yrs

Unified Framework

• Relapsing & Progressive MS diagnosed with same criteria
• ≥2 spinal cord lesions suffice for DIS in progressive onset

Key Radiologic Takeaways

• Optic nerve = 5th site → include in MRI protocol
• DIS now covers 5 zones
• DIT may be omitted only in diagnostic pathways defined by the complete criteria
• CVS & PRL = highly specific diagnostic clues
• kFLC = modern CSF marker alternative
• Older age = confirm with spine, CSF, or CVS

Practical Checklist

• Brain + spine MRI (include orbit protocol if needed)
• Evaluate for CVS, PRLs
• Quantify optic nerve lesions / retinal thinning
• Suggest CSF (OCB or kFLC) correlation
• Comment on differential mimics (SVD, NMOSD, MOGAD)
• “2024 McDonald = MRI-driven, biomarker-backed, globally applicable, early-yet-specific MS diagnosis.”