Mild Cognitive Impairment
The transition from normal aging to Alzheimer’s disease is a subtle one with symptoms emerging gradually. 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, greater 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: The silent stage during which senile plaques are accumulating in the brain, but are insufficient to cause noticeable symptoms.
- Mild Cognitive Impairment (MCI): Symptoms become noticeable to the affected individual and/or family and impairment is significant but does not interfere with everyday activities.
- Dementia: Significant loss of intellectual ability occurs, affecting memory plus one or more other cognitive ability, and the impairment interferes with everyday functioning.
An established risk factor for Alzheimer’s disease, MCI is a condition in which memory and/or other cognitive difficulties (e.g., language, visual-spatial skills) 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 affected cognitive domains (e.g., memory, language). 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, most 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. However, for unknown reasons, some people with MCI remain stable and some even improve. Brain imaging and biomarker studies of people with MCI may help researchers detect early brain changes, like those seen in AD, and assist in determining prognosis for patients with MCI.
Types of MCI
A doctor may diagnose an affected individual with one of the following MCI subtypes:
- Amnestic vs. Non-Amnestic MCI: In amnestic MCI, memory is significantly impaired. Other cognitive functions are spared. Alzheimer’s disease is believed to cause amnestic MCI. In non-amnestic 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.
- Single Domain vs. Multiple Domain MCI: In single domain MCI, only memory or one other domain of cognition is impaired. In multiple domain MCI, memory plus one or more other cognitive abilities are affected.
Individuals with amnestic MCI, single or multiple domain, may be at increased risk for Alzheimer’s dementia. Individuals with non-amnestic MCI may be at increased risk for other dementias, such as fronto-temporal dementia, dementia with Lewy bodies, primary progressive aphasia, and Parkinson’s disease. Having multiple domain MCI appears to increase the risk of future dementia.
Today, researchers and clinicians are unable to definitively predict if MCI will progress to dementia. Numerous studies are underway to identify those neuropsychological, neuropsychiatric, imaging and other features of MCI that might indicate risk for further decline.