Demyelinating and Degenerative Diseases

Demyelinating and Degenerative Diseases

Demyelinating and Degenerative Diseases

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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. Sagittal FLAIR MRI showing Dawson's fingers in MS

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).

FeatureADEM (Acute Disseminated Encephalomyelitis)NMOSD (Neuromyelitis Optica Spectrum Disorder)PML (Progressive Multifocal Leukoencephalopathy)
Onset/CourseMonophasic; post-infectious/vaccinialRelapsing; AQP4-IgG+Progressive; JC virus in immunocompromised
Brain LesionsLarge, fluffy, asymmetric; BG/thalamus commonArea postrema syndrome; often normal earlyAsymmetric, subcortical U-fibers; parieto-occipital
Spinal CordPossible, usually short segmentsLETM (≥3 vertebral segments); "bright spotty"Rare
EnhancementIncomplete rings, nodularVariable; ependymalTypically none
Key ClueChildren/young adults; rapid onsetBilateral optic neuritis; intractable hiccupsImmunocompromised status; "scalloped" lesions

⭐ 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

    SyndromeKey Imaging Feature(s)Clinical Clue
    MSA (Multiple System Atrophy)"Hot cross bun" sign (pons), putaminal atrophy/slit, cerebellar atrophyAutonomic/Cerebellar
    PSP (Progressive Supranuclear Palsy)"Hummingbird" or "Penguin" sign (midbrain atrophy)Vertical gaze palsy
    CBD (Corticobasal Degeneration)Asymmetric frontoparietal cortical atrophyAlien 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.
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Practice Questions: Demyelinating and Degenerative Diseases

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Which of the following symptoms is least likely to be associated with multiple sclerosis?

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Flashcards: Demyelinating and Degenerative Diseases

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T2-weighted MRI brain scans in Hallervorden-Spatz Disease (HSD) shows the _____ sign.

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T2-weighted MRI brain scans in Hallervorden-Spatz Disease (HSD) shows the _____ sign.

eye of the tiger

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