Neurodegenerative diseases

Neurodegenerative diseases

Neurodegenerative diseases

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Neurodegeneration - Protein Power Down

  • Core Mechanism: Misfolded proteins lose normal function & gain toxic properties, resisting degradation and aggregating.
  • Key Proteinopathies:
    • Alzheimer: Aβ plaques, Tau tangles
    • Parkinson/LBD: α-synuclein (Lewy bodies)
    • Huntington: Huntingtin (HTT)
    • Prion Disease (CJD): Prion protein (PrPSc)

Protein Misfolding, Aggregation, and Fibril Formation

Prion-like Spread: Misfolded proteins like α-synuclein and tau can propagate from cell to cell, seeding aggregation in a chain reaction.

Alzheimer Disease - Plaque & Tangle Tussle

  • Pathology: Extracellular senile plaques (β-amyloid) & intracellular neurofibrillary tangles (hyperphosphorylated tau protein).
  • Clinical: Most common cause of dementia. Insidious onset with progressive memory loss (initially short-term), visuospatial deficits, and executive dysfunction.
  • Genetics:
    • Sporadic (late-onset, >95%): Apolipoprotein E4 (ApoE4) is the major risk factor.
    • Familial (early-onset): Mutations in APP (Chr 21), PSEN1 (Chr 14), PSEN2 (Chr 1).
  • Gross: Diffuse cortical atrophy, especially hippocampus → hydrocephalus ex vacuo.

Alzheimer’s Brain Changes: Gross and Microscopic

⭐ Patients with Down Syndrome (Trisomy 21) have an extra copy of the APP gene, leading to a significantly increased risk of early-onset Alzheimer's disease.

Synucleinopathies - The Shakes & Slips

  • Parkinson's Disease (PD): Core motor symptoms 📌 TRAP: Tremor (pill-rolling, at rest), Rigidity (cogwheel), Akinesia/bradykinesia, Postural instability.

    • Pathophysiology: Loss of dopaminergic neurons in substantia nigra pars compacta. Intraneuronal Lewy bodies (α-synuclein aggregates).
  • Lewy Body Dementia (LBD): Features parkinsonism plus early cognitive decline (dementia < 1 year of motor symptoms), fluctuating cognition, and vivid visual hallucinations.

  • Multiple System Atrophy (MSA): Parkinsonism combined with prominent, early autonomic failure (e.g., orthostatic hypotension) or cerebellar signs.

Lewy body formation in neurons

⭐ In LBD, cognitive symptoms appear before or within 1 year of motor symptoms. In PD, dementia is a late complication.

Diverse Pathologies - FTD, HD, ALS & Prions

  • Frontotemporal Dementia (FTD)

    • Degeneration of frontal and/or temporal lobes, leading to behavioral or language deficits.
    • Pathology: Round tau inclusions (Pick bodies) or TDP-43 inclusions.
  • Huntington's Disease (HD)

    • Autosomal dominant; ↑CAG repeats in the HTT gene (anticipation).
    • Marked atrophy of the caudate and putamen.
    • Loss of GABAergic medium spiny neurons.
    • 📌 Choria, Aggressiveness, Grimacing = CAG.
  • Amyotrophic Lateral Sclerosis (ALS)

    • Combined Upper (UMN) & Lower (LMN) motor neuron death.
    • Pathology: TDP-43 inclusions in motor neurons; Bunina bodies (remains of autophagic vacuoles).
  • Prion Disease (e.g., CJD)

    • Pathogenic PrPSc induces misfolding of normal PrPC.
    • Causes spongiform encephalopathy (vacuolization).

Histology of Spongiform Encephalopathy in Prion Diseases

⭐ Creutzfeldt-Jakob Disease (CJD) classically presents as a rapidly progressive dementia with myoclonus and characteristic periodic sharp wave complexes on EEG.

High‑Yield Points - ⚡ Biggest Takeaways

  • Alzheimer's disease is defined by extracellular amyloid-β plaques and intracellular neurofibrillary tangles (hyperphosphorylated tau).
  • Parkinson's disease features Lewy bodies (α-synuclein) and loss of dopaminergic neurons in the substantia nigra.
  • Huntington's disease results from a CAG repeat expansion, leading to caudate and putamen atrophy.
  • ALS combines upper and lower motor neuron signs; look for TDP-43 inclusions.
  • Creutzfeldt-Jakob disease causes rapidly progressive dementia via spongiform encephalopathy.

Practice Questions: Neurodegenerative diseases

Test your understanding with these related questions

An 81-year-old man is brought to the physician by his daughter after he was found wandering on the street. For the last 3 months, he often has a blank stare for several minutes. He also claims to have seen strangers in the house on several occasions who were not present. He has hypertension and hyperlipidemia, and was diagnosed with Parkinson disease 8 months ago. His current medications include carbidopa-levodopa, hydrochlorothiazide, and atorvastatin. His blood pressure is 150/85 mm Hg. He has short-term memory deficits and appears confused and disheveled. Examination shows bilateral muscle rigidity and resting tremor in his upper extremities. He has a slow gait with short steps. Microscopic examination of the cortex of a patient with the same condition is shown. Which of the following is the most likely diagnosis?

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Flashcards: Neurodegenerative diseases

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The number of neurofibrillary tangles in Alzheimer's correlates with degree of _____

TAP TO REVEAL ANSWER

The number of neurofibrillary tangles in Alzheimer's correlates with degree of _____

dementia

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