Introduction
Demyelinating diseases are disorders characterized by destruction of the myelin sheath in the CNS. MRI is the modality of choice for diagnosis, staging, and follow-up.
The most common example is multiple sclerosis (MS), but other demyelinating conditions (ADEM, NMOSD, MOG disease) must also be considered.
MRI Protocol for Demyelinating Diseases
- T1-weighted (± contrast): hypointense “black holes.”
- T2-weighted / FLAIR: hyperintense white matter plaques.
- DWI/ADC: differentiates acute demyelination from stroke.
- Post-contrast T1: shows active lesions (enhancement).
- Spinal cord sequences: sagittal T2, axial T2, STIR.
Typical MRI Findings in Demyelinating Diseases
1. Multiple Sclerosis (MS)
- Brain lesions:
- T2/FLAIR hyperintense plaques in periventricular, juxtacortical, infratentorial, and spinal cord regions.
- “Dawson’s fingers” → ovoid lesions perpendicular to ventricles (classic).
- Black holes on T1 (chronic axonal loss).
- Contrast enhancement → active lesions.
- Spinal cord:
- Short segment (<2 vertebral bodies).
- Peripheral / asymmetric lesions.
2. Acute Disseminated Encephalomyelitis (ADEM)
- Post-infectious or post-vaccination.
- MRI features:
- Large, poorly marginated, asymmetric T2 hyperintensities.
- Involves both white and grey matter (basal ganglia, thalami).
- Usually monophasic.
3. Neuromyelitis Optica Spectrum Disorder (NMOSD)
- Autoimmune against aquaporin-4.
- MRI features:
- Optic nerve: long, bilateral involvement.
- Spinal cord: longitudinally extensive transverse myelitis (≥3 vertebral segments).
- Brain: periependymal lesions around 3rd and 4th ventricles, area postrema.
4. MOG-Associated Disease (MOGAD)
- Anti-MOG antibody-related.
- MRI features:
- Bilateral optic neuritis .
- ADEM-like large lesions in children.
- Spinal cord: longitudinal lesions, often with conus involvement.
| Feature | Multiple Sclerosis (MS) | ADEM | NMOSD | MOGAD |
|---|---|---|---|---|
| Typical Age | Young adults (20–40 yrs) | Children, young adults | Any age (often young females) | Children & young adults |
| Clinical Course | Relapsing–remitting / progressive | Monophasic, post-infection/vaccine | Relapsing, severe attacks | Relapsing, steroid responsive |
| Brain MRI | • Periventricular ovoid plaques (Dawson’s fingers) • Juxtacortical + infratentorial lesions • Black holes on T1 | • Large, asymmetric, poorly marginated lesions • Grey + white matter involvement • Often basal ganglia, thalamus | • Less brain involvement • Lesions around 3rd/4th ventricles, aqueduct, area postrema | • ADEM-like large lesions in children • Cortical/subcortical involvement • Fluffy/ill-defined |
| Optic Nerve | Short segment, unilateral | Can be involved, usually mild | Bilateral, long segment involvement | Bilateral, long & severe optic neuritis |
| Spinal Cord MRI | • Short lesions (<2 vertebral bodies)• Peripheral/asymmetric | • Large but short lesions possible | Longitudinally extensive transverse myelitis (≥3 vertebral segments) | • Long lesions common• Often involves conus medullaris |
| Enhancement | • Variable: active lesions enhance• Incomplete rings possible | • Patchy enhancement | • Variable, cord & optic nerve enhancement | • Patchy or ring-like enhancement |
| Key Differentiator | Dawson’s fingers + short cord lesions | Large, ill-defined, grey + white matter lesions | Long cord lesions + bilateral optic neuritis | Long optic neuritis + conus involvement |
Differential Diagnosis (MRI Clues)
- Ischemia: wedge-shaped, vascular territory, restricted diffusion.
- Tumefactive demyelination: >2 cm, incomplete ring enhancement, less mass effect than neoplasm.
- Infection: rim-enhancing abscess (restricted diffusion).
Key Teaching Points
- MS: Dawson’s fingers, short segment cord lesions.
- ADEM: large, ill-defined, grey + white matter lesions.
- NMOSD: long spinal cord lesions, bilateral optic neuritis.
- MOGAD: optic neuritis + conus medullaris involvement.
- MRI contrast → separates active vs chronic lesions.
âś… Conclusion
MRI is the cornerstone in evaluating demyelinating diseases. By analyzing location, morphology, lesion length, and enhancement patterns, radiologists can differentiate MS from ADEM, NMOSD, and MOG disease — guiding early diagnosis and management.
