Demyelinating and Degenerative Diseases

Demyelinating & Degenerative Diseases - The Great Demyelinator

• Demyelinating diseases: Myelin sheath destruction impairs nerve conduction. Multiple Sclerosis (MS) is the most common.
• Multiple Sclerosis (MS) - Key MRI Features:
  • MRI is vital for diagnosis (McDonald criteria: Dissemination in Space [DIS] & Time [DIT]) and monitoring progression.
  • Lesions: Hyperintense on T2-weighted and FLAIR sequences.
    • Locations (DIS): Periventricular (classic), juxtacortical, infratentorial (brainstem, cerebellum, MCPs), spinal cord. Requires lesions in ≥2 characteristic MS locations.
    • Morphology: Typically ovoid, well-demarcated, >3 mm.
    • Dawson's Fingers: Perpendicular periventricular lesions along medullary veins. Highly specific for MS.
  • Activity Markers (DIT):
    • Gadolinium (Gd) enhancement: Indicates active inflammation, blood-brain barrier (BBB) disruption.
    • New T2/FLAIR lesions or new enhancing lesions on follow-up.
  • Chronic Lesions: T1 hypointense "black holes" reflect severe axonal loss, gliosis.

⭐ Dawson's Fingers: Ovoid demyelinating plaques, perpendicular to lateral ventricles along deep medullary veins, are a highly characteristic imaging sign of Multiple Sclerosis.

Demyelinating & Degenerative Diseases - Not Just MS

Key distinguishing features for MS-like presentations. Compare with MS features (covered previously).

⭐ NMOSD is strongly associated with Aquaporin-4 (AQP4) antibodies and characteristically involves longitudinally extensive transverse myelitis (LETM) spanning ≥3 vertebral segments.

📌 PML = Poor Myelination in Low immunity (JC virus).

Demyelinating & Degenerative Diseases - Brain Drain Breakdown

• Multiple Sclerosis (MS)

  • Key sites: Periventricular (Dawson's fingers), juxtacortical, infratentorial, spinal cord.
  • Active lesions: Contrast enhancement.

• Alzheimer's Disease

  • Hallmark: Medial temporal lobe atrophy, especially hippocampus & entorhinal cortex.

• Parkinson's Disease (PD)

  • Substantia nigra pars compacta degeneration.
  • MRI: Loss of swallow tail sign (nigrosome-1) on SWI.

• Parkinson-Plus Syndromes

  Syndrome	Key Imaging Feature(s)	Clinical Clue
  MSA (Multiple System Atrophy)	"Hot cross bun" sign (pons), putaminal atrophy/slit, cerebellar atrophy	Autonomic/Cerebellar
  PSP (Progressive Supranuclear Palsy)	"Hummingbird" or "Penguin" sign (midbrain atrophy)	Vertical gaze palsy
  CBD (Corticobasal Degeneration)	Asymmetric frontoparietal cortical atrophy	Alien limb phenomenon

• Huntington's Disease

  • Caudate head atrophy → "Boxcar" ventricles.

• ALS (Amyotrophic Lateral Sclerosis)

  • T2/FLAIR hyperintensity along corticospinal tracts.

• Prion Diseases (e.g., CJD)

  • DWI: Cortical ribboning, basal ganglia hyperintensity.
  • vCJD: "Pulvinar sign" or "Hockey stick sign" (thalamus).

⭐ In Progressive Supranuclear Palsy (PSP), the "Hummingbird sign" (or "Penguin sign") on sagittal MRI, indicating severe midbrain tegmentum atrophy with relative pontine sparing, is a highly characteristic finding associated with early postural instability and vertical supranuclear gaze palsy.

High‑Yield Points - ⚡ Biggest Takeaways

• MS: Periventricular lesions, Dawson's fingers, T2 hyperintense, active lesions enhance.
• ADEM: Monophasic, post-infectious, large, fluffy white matter lesions, may involve basal ganglia.
• NMO: LETM (≥3 segments), optic neuritis, AQP4-IgG positive.
• PML: JC virus in immunocompromised, asymmetric white matter lesions, typically no enhancement.
• Alzheimer's Disease: Medial temporal lobe atrophy, especially hippocampus.
• Huntington's Disease: Caudate atrophy, leading to "boxcar" ventricles.
• Parkinson's Disease: Loss of "swallow tail" sign (substantia nigra) on SWI MRI.