Mild Cognitive Impairment

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What is MCI?

  • A clinical condition considered a transition phase between normal aging and dementia.
    • MCI was initially seen as a transition phase between normal aging and Alzheimer’s dementia – however, now recognized that other underlying conditions with different aetiologies may result in mild cognitive impairment that has increased risk of progressing to “dementia.”
  • Peterson et al (1999, 2001) coined term to describe individuals with memory complaints who have objective evidence of memory impairment but whose functioning does not meet currently accepted criteria for clinically probable dementia.
    • subjective memory complaints and objective evidence of mild memory impairment (at a level less than 1.5 standard deviations than health age-matched “normal” peers)
    • normal intellectual functioning
    • normal activities of daily living, and,
    • do not meet currently accepted criteria for clinically probable dementia.
  • Terms used in the past to describe such problems: Malignant Senescent Forgetfulness, Age-Associated Memory Impairment, Late-Life Forgetfulness, Age-Associated Cognitive Decline, Age-Related Cognitive Decline, Mild Cognitive Decline, Mild Neurocognitive Disorder.
  • The use of various terms and inclusion criteria make it difficult to compare studies in the past – there is a need for agreement in definition in order to research 1) estimates of incidence and prevalence, 2) conversion rates to dementia, 3) aetiology, 4) prognosis

Types of MCI

  • Peterson, Doody et al (2001)identified subclassifications of MCI with the primary clinical distinction being the presence or absence of prominent memory impairment
    • Amnestic MCI – probably reflects prodromal phase of dementia
      • Memory complaints, preferably corroborated by informant
      • Impaired memory function on formal testing for age and education level
      • Preserved general cognitive function
      • Intact activities of daily living
      • No evidence of dementia
    • Non-amnestic MCI
      • Mild impairments in one or several domains, including but not limited to language, visual spatial construction, attention, and/or executive functions

Differential Diagnosis

  • Must differentiate from normal aging AND dementia (cognitive impairments and interference with ADLs are more extensive)

Assessment of MCI

  • Some research (XU et al, 2002) suggests combination of Mini-Mental State Exam and Cognitive Capacity Screening Exam showed high sensitivity and specificity for identifying those with MCI who later converted to AD.
  • Neuropsychological assessment should:
    • Take into account patient-related factors such as physical illness, and, psychological and psychiatric comorbidities
      • Anxiety disorders
      • Mood disorders
      • Alcohol and/or other drug abuse
    • Key neuropsychological measures cover (ideally in verbal and nonverbal modalities)
      • Immediate retention of new information
      • Rate and pattern of learning
      • Efficiency of retrieval of recent and remote memory
      • Susceptibility to pro- and retroactive interference
  • Some studies have shown that MCI subjects had markedly lower scores than normals on smell identification tests – may want to include smell assessment in battery but realize that it may be sensitive but not specific
  • Must be aware of and account for sensory impairments on test results

Neuroimaging/ Neuropathology

  • Some evidence of hippocampal atrophy in patient with Amnestic MCI, which was predictive of conversion to AD
  • In individuals with documented MCI prior to death, there was evidence of neurofibrillary tangles and amyloid plaques

Prevalence of MCI

  • Ranges from 3-34% depending on definition and type of sample (community vs. clinical)
  • In general, prevalence of MCI is greater than that of dementia (MCI may be up to 4 times more prevalent than AD when based on community assessment of non-institutionalized individuals)

Progression to AD

  • Amnestic MCI progresses to dementia at a rate of 10-15%
  • Predictors of progression: hippocampal atrophy, genetic susceptibility
  • Remember that there is great heterogeneity in individuals with MCI and not all will progress to AD. Some may progress to other forms of dementia, others show stable cognitive abilities, while still others may show improvement
  • Current research looking at whether medications can alter progression to AD in individuals identified with MCI

Normal Aging (Notes from Lezak’s book)

  • Brain Changes:
    • Rapid shrinkage of brain volume after age 55 in normal adults
    • Cortical atrophy first evident in 40s (widened sulci, narrowed gyri, decrease in cortical mantle)
    • Ventricular dilation
    • Reduced volume in subcortical areas (more in basal ganglia and anterior diencephalons than thalamus)
    • Atrophy due to neuronal loss (or shrinkage in cell size), which is most pronounced in hippocampus and anterior dorsal frontal lobe and least evident in occipital lobes
    • Cerebral blood flow studies show progressive decline is greatest in prefrontal and inferior temporal cortex and least evident in occipital areas
  • Overall Cognition:
    • methodological differences between studies have produced contradictory results
    • “crystallized” knowledge shows gains into 70sand 80s while “fluid” intelligence show slow decline in middle years and more rapid decline following 50s or 60s
    • some suggest that slowing (psychomotor and cognitive), executive dysfunction or visuospatial deficits may account for much of the performance decline seen with increased age.
    • No change in cerebral asymmetry of laterality of functions with age.
  • Sensory and Motor Changes:
    • Senses decline in sensitivity and acuity
      • visual and auditory losses first evident in 40s and 50s but rapid decline seen after 60s. Into 70s and 80s, only a minority (~10-30%) have normal vision or hearing.
      • Also see decline in olfaction after 40s.
    • Response times increase and fine motor abilities decline:
      • Reaction time begins to gradually decline in 30s and continues at a steady rate
      • Mental processing slows dramatically in 60s
      • Slowing limits performance on timed tests (WAIS Performance subtests)
      • Diminished motor strength appears in 40s with accelerated losses thereafter.
  • Attentional Changes:
    • simple span measures remain intact until 80s
    • however, older people have more difficulty with divided attention (e.g., choice reaction time tests) and there are declines in sustained and selective attention.
  • Memory Changes:
    • short-term retention on simple span measures is most resistant to age-related declines
    • older people have more difficulty than younger in tests of supraspan (i.e., amount of material exceeds normal storage capacity)
    • performance on working memory tasks declines with age
    • learning efficiency diminishes with age and losses are most evident on spontaneous recall (rather than recognition)
    • visual recall (tested by recall or recognition formats) declines more quickly than verbal memory and shows sharper declines in later years.
    • Auditory and tactile memory show rapid decline between 40 and 60
    • Accuracy of source memory decreases with age
    • Verbal memory performance least compromised with normal aging.
  • Verbal Abilities:
    • most verbal abilities do not decline with age (i.e., vocabulary and verbal reasoning are stable over time).
    • Difficulty with verbal retrieval (i.e., poor access to verbal memory) is common complaint among elderly and is evident on formal testing (i.e., decreased verbal fluency, requires more cues on BNT to aid word retrieval).
  • Visuospatial Functions / Praxis:
    • visuoperceptual judgement declines steadily from 65 on into the 90s
    • general difficulties with visuoperceptual organization seen in people ages 70 to 90 years.
    • Spatial orientation is also sensitive to aging
    • No real change in praxis, although older people more likely to use body part as object
    • Decreased performance on WAIS BD and OA is due more to speed than visual abilities
  • Reasoning, Concept Formation, Mental Flexibility:
    • reasoning about familiar material shows no age-related decline, however, there is a decline in reasoning in novel or complex situations
    • decline in concept formation and abstraction; older people tend to be more concrete (especially after the age of 70)
    • mental inflexibility seen in difficulty adapting to new situations, solving new problems and changing mental set
  • Heath and Cognitive Aging
    • older people more lively to have health problems that are known to affect cognition (i.e., diabetes, hypertension,…)
    • regular exercise may slow rate of cognitive decline or even reverse it