Multiple sclerosis (MS)
Revised McDonald criteria 2024
Multiple sclerosis (MS) is a chronic autoimmune inflammatory disease affecting the central nervous system (CNS), characterized by demyelination, axonal damage, and neurodegeneration .
The 2024 McDonald criteria represent the most recent revision of diagnostic guidelines, incorporating advanced imaging biomarkers and expanding diagnostic capabilities to enable earlier and more accurate MS diagnosis .
Dissemination in space (DIS)
The McDonald criteria originally necessitate the presence of at least one white matter hyperintensity in a minimum of two characteristic locations, including periventricular, juxtacortical, infratentorial regions (such as the brainstem), and the spinal cord, to demonstrate dissemination in space (DIS). The new criteria now include the optic nerve as a fifth topographic location for dissemination in space, alongside traditional locations (periventricular, cortical/juxtacortical, infratentorial, and spinal cord).
Two new MRI biomarkers have been incorporated: the central vein sign (CVS) and paramagnetic rim lesions (PRLs), both providing greater than 90% specificity for MS diagnosis . These imaging markers can facilitate earlier diagnosis, particularly in patients with radiologically isolated syndrome (RIS) .
Dissemination in time (DIT)
Dissemination in time (DIT) is indicated by the coexistence of lesions with and without contrast enhancement at any point, or by the appearance of new high-signal lesions on T2WI or lesions with contrast enhancement during follow-up MRI.
CSF markers
The 2024 revision of the McDonald criteria represents a significant advancement in diagnostic methodology, incorporating kappa free light chains (κ-FLC) as an equivalent biomarker to oligoclonal bands (OCB) for detecting intrathecal immunoglobulin synthesis .
Periventricular and juxtacortical lesions
The most pathognomonic imaging marker of the periventricular region is Dawson's fingers, which appear as finger-like lesions extending radially from the lateral ventricles . These lesions are optimally visualized on FLAIR sequences and represent perivenular demyelination arranged perpendicular to the ventricular surface.
Corpus callosum involvement presents as multiple small lesions at the callososeptal interface, creating the "Venus necklace sign", demonstrating multiple, nodular, radiating signal abnormalities and irregular ependymal thickening.
The term "juxtacortical" specifically refers to lesions that directly contact the cortex, involving the subcortical U-fibers. Juxtacortical lesions are optimally visualized on FLAIR sequences, where they appear as hyperintense lesions directly contacting the cortical surface.
Paramagnetic rim lesions (PRLs) appear on susceptibility-weighted imaging as lesions with paramagnetic rims reflecting iron accumulation in microglia at lesion edges . PRLs are found in approximately 50% of patients and are associated with higher levels of MS pathology.
The central vein sign (CVS) appears as a thin hypointense line or small hypointense dot on T2*-weighted sequences or susceptibility-weighted images, visible in at least two perpendicular MRI planes . The CVS has a small apparent diameter (<2 mm), runs partially or entirely through the lesion, and is positioned centrally within the lesion.
Infratentorial lesions
Infratentorial lesions show preferential distribution with the medulla involved in 90% of cases, pons in 85%, and midbrain in 80% of patients, followed by cerebellar lesions.
Spinal cord lesions
The lesions are typically short in cranio-caudal diameter, usually covering less than two vertebral segments and occupying less than half of the cord cross-sectional area. On sagittal images, lesions appear cigar-shaped, while axial sequences reveal wedge-shaped configurations.
The cervical spinal cord demonstrates the highest predilection for MS lesions, with lesions occurring more frequently in the upper cervical segments (C1-C3) compared to lower cervical levels (C4-C7). Thoracic spinal cord involvement appears to be significantly influenced by the degree of cervical spine lesion burden, with patients having more than two cervical lesions showing substantially increased odds of thoracic involvement.
Optic nerve
The 2024 McDonald criteria incorporate the optic nerve as the fifth topographic location for dissemination in space. Optic nerve evaluation utilizes fat-suppressed T2-weighted images and gadolinium-enhanced T1-weighted sequences.