Harvey's Garden

Memory impairment

3 min read

Physiology

  • Classification of Memory
    • Sensory Memory: < 1 second; immediate processing of sensory info.
    • Short-term (Working) Memory: Seconds to minutes; limited capacity (7 ± 2 items).
      • Dependent on Prefrontal Cortex.
    • Long-term Memory:
      • Explicit (Declarative): Conscious recall of facts/events.
        • Episodic: Personal experiences/events.
        • Semantic: Factual knowledge (e.g., names of colors).
        • Anatomy: Hippocampus (medial temporal lobe) & Diencephalon.
      • Implicit (Non-declarative): Unconscious skills.
        • Procedural: Skills/motor tasks (e.g., riding a bike).
        • Anatomy: Basal Ganglia (striatum) & Cerebellum.
        • Emotional conditioning: Anatomy: Amygdala.
  • Anatomical Localizations
    • Hippocampus: Consolidation of Short-term → Long-term memory.
      • Damage results in Anterograde Amnesia (inability to form new memories).
      • Very sensitive to hypoxic-ischemic injury (e.g., stroke, cardiac arrest).
    • Mamillary Bodies: Part of the Papez circuit.
      • Lesioned in Wernicke-Korsakoff Syndrome.
    • Frontal Lobe: Working memory and executive function.
    • Amygdala: Fear conditioning and emotional memory.

High-Yield Clinical Syndromes

  1. Memory Loss (Impairment): The symptom.
  2. Amnesia: A specific clinical syndrome where memory loss is the primary or sole deficit.
    • Anterograde Amnesia: Inability to form new memories after the inciting event.
      • Primary deficit in consolidation (short-term long-term).
      • Associated with damage to the hippocampus and parahippocampal cortex.
    • Retrograde Amnesia: Inability to recall events prior to the inciting event.
      • Often temporally graded (recent memories lost first; remote memories spared).
  3. Dementia: A broad disease process where memory loss is just one component of global cognitive failure.

Tip

  • Short-term memory loss: most forms of dementia
  • Long-term memory loss: semantic dementia, a type of frontotemporal dementia (FTD)
  • Alzheimer’s Disease:
    • Gradual, progressive short-term memory loss first, then other cognitive decline.
    • Patho: Amyloid plaques, tau tangles, hippocampal atrophy.
    • Genetics: APOE4 (late), APP/PSEN1/2 (early).
  • Vascular Dementia:
    • Stepwise decline or sudden onset after stroke; focal neuro deficits common.
    • Hx: Stroke, TIA, cardiovascular risk factors.
    • Imaging: Shows infarcts/white matter lesions.
  • Lewy Body Dementia:
    • Fluctuating cognition, visual hallucinations (detailed), Parkinsonism (often after cognitive sx).
    • REM sleep behavior disorder. Sensitive to antipsychotics.
    • Patho: Alpha-synuclein (Lewy bodies) in cortex.
  • Frontotemporal Dementia (FTD):
    • Early personality/behavior changes (disinhibition, apathy) OR aphasia. Memory relatively spared early.
    • Younger onset typical.
    • Patho: Frontal/temporal lobe atrophy; Pick bodies (tau) in some.
  • Delirium:
    • Acute onset, fluctuating course, impaired attention & consciousness.
    • Caused by underlying illness, drugs, withdrawal. Reversible.
  • Depression (Pseudodementia):
    • Patient complains prominently of memory loss; “don’t know” answers.
    • Associated mood symptoms (sadness, anhedonia, sleep/appetite changes).
    • Improves with depression treatment.
  • Normal Pressure Hydrocephalus (NPH):
    • Triad: Dementia, gait disturbance (magnetic), urinary incontinence. “Wet, Wobbly, Wacky.”
    • Ventricular enlargement on imaging. Potentially reversible with shunting.
  • Wernicke-Korsakoff Syndrome:
    • Thiamine (B1) deficiency (often alcoholism).
    • Wernicke (acute): Confusion, Ataxia, Ophthalmoplegia (nystagmus, CN VI palsy).
    • Korsakoff (chronic): Anterograde amnesia, confabulation, mamillary body atrophy.
  • Vitamin B12 Deficiency:
  • Hypothyroidism:
    • Cognitive slowing, memory issues, fatigue, other systemic signs of low thyroid.

General Approach:

  1. Onset/Progression: Acute (delirium) vs. Gradual (dementias) vs. Stepwise (vascular).
  2. Key Symptoms: What stands out? (Hallucinations? Personality change? Gait issues?).
  3. Associated Signs: Focal deficits? Parkinsonism? Neuropathy?
  4. Reversibility: Always consider and rule out reversible causes (Delirium, Depression, NPH, B12/Thyroid, Meds).

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