Detailed Notes on Dementia and Degenerative Disorders

Introduction to Dementia and Degenerative Disorders

  • Focus on degenerative nature, involving the loss of neurons in the brain

  • Identifying regions: gray matter, white matter, and deeper structures like basal ganglia

Key Concepts of Degenerative Disorders

  • Loss of neurons can result in:

    • Dementia: Caused by degeneration of neurons in the cerebral cortex

    • Movement Problems: Resulting from degeneration in the basal ganglia

Alzheimer's Disease

  • Most common cause of dementia

    • Involves cortical neurons, leading to memory and cognitive decline

  • Amyloid Precursor Protein (APP):

    • Cleaved by enzymes, can produce beta-amyloid, which accumulates and forms plaques in Alzheimer’s patients.

  • Clinical Features:

    • Slow onset memory loss (recent memories first)

    • Cognitive dysfunction without loss of consciousness

    • Later stages lead to disorientation, loss of language skills, personality changes, and bedridden state

    • No early focal neurological deficits (no Parkinson’s or Huntington symptoms at onset)

  • Epidemiology:

    • Mainly sporadic, age is a significant risk factor

    • Epsilon-4 allele of ApoE increases risk; epsilon-2 allele decreases risk

    • Early-onset Alzheimer’s related to family mutations (e.g., presenilin genes) and Down syndrome association due to extra APP on chromosome 21

Pathological Features of Alzheimer's Disease

  1. Diffuse Cerebral Atrophy:

    • Narrowing of gyri and widening of sulci, leading to hydrocephalus ex vacuo (ventricle dilation due to atrophy)

  2. Neuritic Plaques:

    • Composed of amyloid deposits and neuritic processes, causing Alzheimer’s pathology

  3. Neurofibrillary Tangles:

    • Contain hyperphosphorylated tau protein; disrupts microtubule organization

Other Types of Dementia

  • Vascular Dementia:

    • Caused by impaired blood flow due to conditions like hypertension or atherosclerosis, leading to brain injury

    • Multilevel infarctions contribute to dementia symptoms

  • Pick's Disease:

    • Affects frontal and temporal lobes, causing behavioral changes and language issues early on

    • Identified by round aggregates of tau protein

  • Parkinson’s Disease:

    • Loss of dopaminergic neurons in the substantia nigra, leading to movement disorders

    • Characterized by tremors, rigidity, bradykinesia, and postural instability (mnemonic: TRAP)

    • Presents with pigmented neuron loss and Lewy bodies composed of alpha-synuclein

  • Huntington’s Disease:

    • Loss of GABAergic neurons in the caudate nucleus leads to chorea and involuntary movements

    • Genetic factor: CAG trinucleotide repeat associated with anticipation

Other Contributing Factors to Dementia

  • Normal Pressure Hydrocephalus:

    • Caused by increased CSF leading to dilation of ventricles, causing the triad of urinary incontinence, gait instability, and dementia ("wet, wacky, and wobbly")

  • Spongiform Encephalopathy (e.g., CJD):

    • Progressively fatal condition leading to rapidly progressing dementia

    • Characterized by spongy pathology due to misfolded prion proteins, causing characteristic vacuolation

    • Variant CJD associated with younger ages and beef consumption

  • Familial Fatal Insomnia:

    • Inherited form causing insomnia and exaggerated startle response