Mild Cognitive Impairment

MCI: Transition from Normal Aging to Dementia

The transition from normal aging to Alzheimer’s disease is a subtle one with symptoms emerging gradually.  Oftentimes, the development of Alzheimer’s disease is compared to the dimming of a light, as cognitive abilities are slowly lost over time.

Everyone can expect to experience cognitive changes as they age.  Common changes associated with normal aging include slower recall of information such as names, increased effort to learn and store new information, heightened susceptibility to distraction, slower processing of new information, and greater difficulty multi-tasking.

Scientists and clinicians describe three stages in the development and progression of Alzheimer’s disease.

  • Pre-clinical or pre-symptomatic phase, that is, the silent stage during which senile plaques are accumulating in the brain, but are insufficient to cause noticeable symptoms.
  • Mild Cognitive Impairment (MCI) in which symptoms become noticeable to the affected individual and/or family and impairment is significant but does not interfere with everyday activities, as described further below.
  • Dementia, in which significant loss of intellectual ability occurs, memory plus one or more other cognitive abilities are affected, and the impairment is so severe as to interfere with everyday functioning.
Progression from normal aging to Alzheimer's disease or another dementia

Progression from normal aging to Alzheimer’s disease or another dementia

Mild Cognitive Impairment (MCI)

An established risk factor for Alzheimer’s disease, Mild Cognitive Impairment (MCI) is a  condition in which memory and/or other cognitive difficulties (e.g., language, visual-spatial skills) disrupt everyday life (e.g., missing appointments) and are noticeable to the person affected and/or others (e.g., family, friends, work colleagues), but are not severe enough to interfere with basic living skills.  An individual with MCI will score significantly lower than others of the same age on neuropsychological measures of the particular cognitive domains (e.g., memory, language) affected. Some studies suggest that up to 10-20% of older adults age 65 and older have MCI.  MCI may be caused by a variety of medical and mental health (e.g., depression) conditions as well as be a precursor to a progressive dementia like AD.  Over time, the vast majority of individuals diagnosed with MCI do progress (or “convert”) to AD.  Overall, studies estimate that 10-15% of people with MCI progress to AD each year.  Although, for yet unknown reasons, some people with MCI remain stable and a few even improve, MCI is widely viewed as a transitional state between normal aging and AD or another dementia.  Brain imaging and biomarker studies of people with MCI may help researchers detect early brain changes like those seen in AD. Such research could lead to a better understanding of how MCI develops as well as early detection and diagnosis.

Types of Mild Cognitive Impairment

There are three main subtypes of MCI.  A doctor may diagnose an affected individual with one of the following MCI subtypes.

Amnestic Single Domain MCI: In amnestic single domain MCI, only memory is significantly impaired. Other cognitive functions are spared.  Alzheimer’s disease is believed to cause amnestic MCI.  Consequently, someone with this diagnosis is at high risk for developing the full-blown dementia of AD.

Amnestic Multiple Domain MCI: In amnestic multiple domain MCI, memory plus one or more other cognitive abilities are affected.  Research suggests that the underlying causes of amnestic multiple domain MCI include normal aging, vascular dementia, and Alzheimer’s disease.

Single or Multiple Non-Memory MCI: In this form of MCI, memory remains intact, but one (single domain) or more (multiple domain) other cognitive abilities (e.g., language, visual-spatial skills, executive functioning) are significantly impaired.  Likely causes of single or multiple domain MCI include fronto-temporal dementia, dementia with Lewy bodies, primary progressive aphasia, and Parkinson’s disease.

Today, researchers and clinicians are unable to definitively predict if MCI will progress to Alzheimer’s disease or another dementia.  Numerous studies are underway to identify those neuropsychological, neuropsychiatric, imaging and other features of MCI that might indicate risk for further decline.