Mild Neurocognitive Disorder / Mild Cognitive Impairment (MCI)

Primer

Mild Neurocognitive Disorder (also known as Mild Cognitive Impairment, or MCI) is a condition in which individuals demonstrate cognitive impairment with minimal impairment of instrumental activities of daily living (IADLs). Although it can be the first cognitive sign of Alzheimer's Disease (AD), it can also be secondary to other disease processes (e.g. - neurologic, other neurodegenerative disorders, systemic, infectious, or psychiatric disorders). When there is interference with independence in everyday activities, a major neurocognitive disorder needs to be considered instead.

Epidemiology
  • Prevalence is between 10-20% in adults over 65 years.
Prognosis
  • Anywhere between 3 to 13% of patients with mild neurocognitive disorder will progress to a major neurocognitive disorder (dementia) each year.[1]
  • Not all individuals with MCI will go on to develop a dementia!
    • This is a highly heterogeneous group with variable rates of conversion to dementia.
    • For example, having multiple domain MCI appears to increase the risk of future dementia.
Comorbidity
  • Neuropsychiatric symptoms will be present in 35-75% of cases.
Risk Factors
  • Higher age, the presence of at least one ApoE4 allele, and medicated hypertension are independent risk factors for MCI.[2]
  • Higher education is a protective factor for MCI.

DSM-5 Diagnostic Criteria

Criterion A

Evidence of modest cognitive decline from a previous level of performance in 1 or more cognitive domains (complex attention, executive function, learning and memory, language, perceptual motor, or social cognition) based on:

  1. Concern of the individual, a knowledgeable informant, or the clinician that there has been a significant decline in cognitive function; and
  2. A substantial impairment in cognitive performance, preferably documented by standardized neuropsychological testing or, in its absence, another quantified clinical assessment.
Criterion B

The cognitive deficits do not interfere with capacity for independence in everyday activities (i.e. - complex instrumental activities of daily living such as paying bills or managing medications are preserved, but greater effort, compensatory strategies, or accommodation may be required).

Criterion C

The cognitive deficits do not occur exclusively in the context of a delirium.

Criterion D

The cognitive deficits are not better explained by another mental disorder (e.g., major depressive disorder, schizophrenia).

Specifiers

Etiology Specifier

Behaviour Specifier

Specify:

  • Without behavioural disturbance: If the cognitive disturbance is not accompanied by any clinically significant behavioral disturbance.
  • With behavioural disturbance (specify disturbance): If the cognitive disturbance is accompanied by a clinically significant behavioural disturbance (e.g. - psychotic symptoms, mood disturbance, agitation, apathy, or other behavioural symptoms).

Subtypes

The DSM-5 diagnostic criteria notably do not provide additional sub-typing of MCI beyond the specifier criteria or how cognitive domains are specifically involved. Outside of the DSM-5, a total of 4 MCI subtypes have been proposed, depending on whether the presentation is amnestic/non-amnestic, and single/multiple domain:[3]

  1. Amnestic MCI, Single Domain (a-MCI-sd)\
    • a-MCI-sd involves primarily memory impairment with no or minimal involvement of the other cognitive domains.
  2. Amnestic MCI, Multiple Domain (a-MCI-md)
    • a-MCI-md involves memory impairment as the primary domain affected, but other cognitive domains (e.g. - executive function, attention, language, decision-making, judgment, visuospatial) are also impaired.
  3. Non-Amnestic MCI, Single Domain (na-MCI-sd)
    • na-MCI-sd involves impairment of a single, non-memory cognitive domain, such executive function, attention, language, or visuospatial skills.
  4. Non-Amnestic MCI, Multiple Domain (na-MCI-md)
    • na-MCI-md involves impairment of two or more cognitive domains, neither of which involves memory impairment.

Differential Diagnosis

  • Some cases of MCI are actually reversible causes of cognitive impairment. This is a broad differential diagnosis that includes medication side effects, obstructive sleep apnea, depression (pseudodementia), and other medical conditions. Medications such as benzodiazepines may also contribute to cognitive impairment and so deprescribing may also be an important factor to consider.

Management

Monitoring and Counselling

  • Clinicians should counsel patients with MCI and their families to discuss long-term planning topics such as advance directives, driving safety, finances, and estate planning.[4]
  • For patients diagnosed with MCI, clinicians should perform serial cognitive assessments over time (e.g., a MoCA every 6 to 12 months) to monitor for changes in cognitive status.[5]
  • Neuropsychiatric symptoms should also be serially assessed for, as these may be more functionally impairing than the cognitive symptoms.

Exercise

  • Exercise at least twice weekly of moderate intensity may provide benefits in cognition for individuals with MCI.[6]

Pharmacologic

  • There are no high-quality, long-term studies suggesting that either pharmacologic or dietary agents can improve cognition or delay progression in patients with MCI.[7]
  • Acetylcholinesterase inhibitors as a class have shown no benefit on cognitive outcomes or reduction in progression from MCI to dementia (although some studies could not entirely exclude a positive effect). In addition to lacking efficacy, the side effects of cholinesterase inhibitors can be significant.[8] If an individual is prescribed an acetylcholinesterase inhibitor, they should be counselled that this is off-label.

References

1) Farias, S. T., Mungas, D., Reed, B. R., Harvey, D., & DeCarli, C. (2009). Progression of mild cognitive impairment to dementia in clinic-vs community-based cohorts. Archives of neurology, 66(9), 1151-1157.
2) Tervo, S., Kivipelto, M., Hänninen, T., Vanhanen, M., Hallikainen, M., Mannermaa, A., & Soininen, H. (2004). Incidence and risk factors for mild cognitive impairment: a population-based three-year follow-up study of cognitively healthy elderly subjects. Dementia and geriatric cognitive disorders, 17(3), 196-203.
3) Rapp, S. R., Legault, C., Henderson, V. W., Brunner, R. L., Masaki, K., Jones, B., ... & Thal, L. (2010). Subtypes of mild cognitive impairment in older postmenopausal women: the Women’s Health Initiative Memory Study. Alzheimer disease and associated disorders, 24(3), 248.
4) Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S., Ganguli, M., Gloss, D., ... & Rae-Grant, A. (2018). Practice guideline update summary: Mild cognitive impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126-135.
5) Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S., Ganguli, M., Gloss, D., ... & Rae-Grant, A. (2018). Practice guideline update summary: Mild cognitive impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126-135.
6) Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S., Ganguli, M., Gloss, D., ... & Rae-Grant, A. (2018). Practice guideline update summary: Mild cognitive impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126-135.
7) Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S., Ganguli, M., Gloss, D., ... & Rae-Grant, A. (2018). Practice guideline update summary: Mild cognitive impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126-135.
8) Petersen, R. C., Lopez, O., Armstrong, M. J., Getchius, T. S., Ganguli, M., Gloss, D., ... & Rae-Grant, A. (2018). Practice guideline update summary: Mild cognitive impairment: Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology, 90(3), 126-135.