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Alzheimer’s Dementia



  • Exact underlying pathogenesis remains uncertain
    • Related to neuronal death due to plaques and neurofibrillary tangles
    • Possibilities include tau proteins and beta-amyloid as culprits
    • Genetic link postulated



  • Memory impairment (short-term initially, progressing to longer-term)
  • Visuospatial impairment (difficulties with car parking, dropping items)
  • Planning (meal-cooking, complex tasks)
  • Word-finding problems
  • Disorientation to time and place
  • Labile mood as disease progresses with occasional delusions and dangerous behaviour


Diagnosis of Alzheimer’s dementia

  • The staging of the level of severity of Alzheimer’s as a disease process can be broken down into 3 separate entities:
    • Alzheimer’s Dementia
    • Alzheimer’s related mild cognitive impairment (MCI)
    • Pre-clinical Alzheimer’s
  • The criteria from each stage is based on recommendations  from the National Institute on Aging -Alzheimer’s Association workgroups; full studies can be found here.
  • In summary, to diagnose dementia the follow need to be present:
    • Interferes with activities of daily living (ADLs)
    • A decline in function noted over time
    • This decline is not attributable to short-term or reversible causes (e.g. delirium)
    • The impairment in cognition is obtained (as described in the general dementia section) via history, collateral history, and bedside cognitive testing.
    • Multi-domain impairment documented in cognition, of at least two of:
      • Memory impairment
      • Reasoning and judgement
      • Visuospatial
      • Language
      • Behaviour/personality
  • With regards to a specific diagnosis of Alzheimer’s dementia, this is again sub-divided into 3 separate categories:
    • Probable Alzheimer’s Dementia
    • Possible Alzheimer’s Dementia
    • Probably or possible Alzheimer’s Dementia with evidence of pathophysiological process
  • Each sub-category has been defined as detailed below (each with the pre-requisite of a diagnosis of all-cause dementia as detailed above).


Probable Alzheimer’s Dementia

  • Insidious onset over months to years, rather than more acutely of hours to days
  • Definitive history of worsening of cognition over time
  • One of the following categories are present as the most prominent finding during clinical assessment:
    • Amnesic presentation (most common)
    • Non-amnesic presentations:
      • Language (e.g. word/name finding difficulties)
      • Visuospatial (e.g. facial recognition deficit)
      • Executive (e.g. impairment judgement and task planning)
    • Without any of the following findings present:
      • Significant cerebrovascular disease (e.g. significant stroke associated contemporaneously with onset of cognitive impairment)
      • Findings of the core features of Lewy Body Dementia (e.g. hallucinations, Parkinsonism etc… for more details see the LBD section)
      • Findings in keeping with fronto-temporal dementia
      • Findings in keeping with progressive aphasia
      • Concurrent neurological disease


Possible Alzheimer’s Dementia

  • Atypical Course
    • Clinical findings and features of Alzheimer’s Dementia but with an unusual time course (e.g. fast onset, rapid decline)
  • Mixed Presentation
    • Mixed with signs of Vascular Dementia
    • Mixed with signs of LBD
    • Mixed with other concurrent neurological disease


Probable Alzheimer’s Dementia with evidence of pathophysiological process

  • If the additional pathophysiological processes are identified, it increases the likelihood of the underlying disease process being that of an Alzheimer’s Dementia (remembering that a true diagnosis can only be confirmed at autopsy!)
  • It is not recommended that these biomarkers are routinely looked for in the diagnosis, due to ongoing research into the pathological process and the variability in availability and sensitivities of appropriate assays to detect them. More information is included for reference only.
  • Biomarkers of brain amyloid-beta protein deposition:
    • Low CSF Aβ42
    • Positive PET amyloid imaging
  • Biomarkers of downstream neuronal injury or degeneration:
    • Elevated CSF Tau
    • Decreased fluorodeoxyglucose (FDG) uptake on PET in temporal-parietal cortex
    • Disproportionate atrophy on MRI of:
      • Medial, basal, and lateral temporal lobe
      • Medial parietal cortex


Click here to learn about the diagnosis and management of dementia


Click here to learn about cognitive assessment in dementia