A Multifactor Approach to Mild Cognitive Impairment

Taha Qarni, BHSc; Arash Salardini, MD

Disclosures

Semin Neurol. 2019;39(2):179-187. 

In This Article

Moving Beyond MCI

a. Severity-based subcategories of MCI: It is not clear whether MCI should be treated as a binary category or have subcategories representing different stages of progression. The Alzheimer's Disease Neuroimaging Initiative (ADNI) proposed a classification system for those patients with memory complaints who did not have dementia.[49,50] The categorization was as follows:

  1. Memory recall > 1.5 SD below normal was classified as late MCI.

  2. Memory recall falling between 1 and 1.5 SD below normal was classified as early MCI.

  3. Memory recall of 1 SD below normal or better was classified as subjective memory complaints.

In one systematic review of the evidence using these criteria, the researchers found that those with late MCI had a much higher rate of conversion to dementia compared with both subjective memory impairment (SMI) and early MCI, both of the latter of which had comparable rates of conversion.[51] This may suggest that early MCI might represent a different stage of disease compared with late MCI. The overlap between early MCI and SMI may be partly driven by the participation of more educated and more motivated individuals in studies, such as ADNI and comparable cohorts, who would at baseline perform better than expected. Educational norming removes some of this bias but clearly not all.

b. Early noncognitive decline as a prodrome of dementias: Cognition is not the only area affected by dementia. MCI as a category was conceived with AD in mind. In AD, there is a relative sparing of behavior and the functions of the primary cortical areas. For this reason, there has been a lack of emphasis on noncognitive symptoms in MCI and early dementia. Behavioral issues are common in frontally localized neurodegenerative diseases. Motor dysfunction is common in subcortical dementias. To ameliorate this, efforts have been made to identify these categories especially in the early course of dementias.

• Motoric cognitive risk (MCR) syndrome: The term has not yet found the circulation it deserves. It was developed by Joe Verghese and his colleagues in both cognitive neurology and geriatrics.[52] The need for a new category arose from the links between cognition and gait apraxia seen in subcortical dementias, especially vascular disease associated with aging. For example, it is known that:

  1. Slow gait predicts risk of dementia independent of cognitive status.[53]

  2. Gait slowing precedes MCI symptoms.[54]

  3. MCI corresponds to slower gait speed.[55]

The following diagnostic criteria were proposed that need to be satisfied to make a diagnosis of MCR:

  1. Presence of subjective cognitive problems, as demonstrated on a formal questionnaire or instrument.

  2. Slowing of gait speed of more than 1 SD.

  3. Preserved mobility.

  4. No dementia.

• Mild behavioral impairment: Less well developed is the concept of mild behavioral impairment. Presently, it is too broad to be of specific value because it tends to include all possible noncognitive neuropsychiatric changes, many of which are common in the elderly. However, diagnostic criteria such as ones by the International Society to Advance Alzheimer's Research and Treatment – Alzheimer's Association[56] represent progress in the status quo. The following criteria are proposed that need to be satisfied in people older than 50 years with symptoms for more than 6 months (albeit intermittently):

  1. Decrease in motivation, affective regulation, social appropriateness, impulse control, or thought/perceptual content.

  2. These can interfere with relationships, social, or vocational functioning.

  3. These cannot be explained in other ways.

  4. There is no dementia.

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