Clinical Geriatrics

Introduction
Mild cognitive impairment (MCI) is an emerging term for an intermediate stage between cognitive changes of normal aging and dementia in elderly people. While normal aging is a gradual decline in cognition, MCI refers to cognitive impairment beyond that expected for age and education, but does not meet criteria for dementia.¹ As the population ages and longevity increases, physicians will increasingly see patients experiencing memory loss, so learning an approach to states such as MCI is now warranted. Primary care physicians should be aware that dementia is preceded by a recognizable phase of MCI. They should be familiar with the concept of MCI and other similarly used terms, including cognitive impairment, not dementia (CIND). Physicians should closely monitor patients with MCI because of their increased risk of developing dementia.

Definition
The diagnostic term mild cognitive impairment refers to early, nondisabling cognitive disorders that do not meet the criteria for dementia. Although many researchers proposed a variety of criteria, the Mayo criteria are the ones most applied in the literature^2,3:

• Self-reported memory complaint, preferably corroborated by an informant
• Objective memory impairment
• Preserved general cognitive function
• Intact activities of daily living (ADL) with minimal impairment in instrumental functions
• Not meeting criteria for dementia

Making the distinction between normal impairments of aging and impairments that do not represent dementia requires considerable clinical judgment that may differ among assessors.⁴ Challenges remain for lack of a uniform quantitative or systematic definition of functional impairment. The Clinical Dementia Rating (CDR) scale5 has been used in research studies and has proven to be a valuable instrument for the definition of functional impairment; however, for practical clinical application, it is too time-consuming.

Subclassifications
MCI is now recognized as heterogeneous with three accepted subclasses: (1) amnestic MCI; (2) multiple-domain MCI; (3) and single nonmemory domain MCI.⁶ Each MCI subtype can then be classified according to the presumed etiology: degenerative; vascular; psychiatric; or traumatic.

Amnestic MCI refers to the monosymptomatic amnestic form and is often used for those individuals presumed to have a MCI of degenerative etiology. Memory impairments are generally represented by defects that are 1.5 standard deviations (SD) or more below age- and education-corrected norms. Amnestic MCI is the subtype most specifically correlated with Alzheimer’s disease (AD) and is used to define a “predementia” state amenable to therapeutic interventions. The efficacy of such interventions is defined by the rate of conversion from MCI to dementia.⁴

Multiple-domain MCI refers to patients with impairment in multiple domains of cognitive and behavioral functioning with and without memory impairment. The multiple domains are only slightly impaired, no more than 0.5 SD below age- and education-matched normal subjects. Patients may manifest subtle problems with ADL but do not meet the criteria for a formal diagnosis of dementia. Patients with multiple-domain MCI may progress to AD or vascular dementia (VaD), or revert to a baseline functioning over time.⁷

Single nonmemory domain MCI refers to the monosymptomatic impairment other than memory loss.