Box 1. Characteristics of dementia and mild cognitive impairment.

Dementia27

The loss of cognitive abilities must be:

• Present in several cognitive domains (often memory with at least one other domain such as language, visuospatial, executive, or other), and

• Represent a decline from the prior level of function, and

• Impair functional abilities in day-to-day life (e.g., social, occupational, self-care)

The most common form of dementia is a “mixed dementia”,* usually a combination of a:

• Common neurodegenerative disease in aging, most often Alzheimer’s disease (AD), and

• Vascular contributions to cognitive impairment and dementia (VCID)

Common neurodegenerative diseases causing dementia include the following, in decreasing order of frequency:**

• AD

• Lewy body disease

• Frontotemporal dementia***

Mild cognitive impairment (MCI)28

The loss of cognitive abilities must be:

• Demonstrable on cognitive testing, whether amnestic versus non-amnestic MCI, or single versus multi-domain MCI (present in several cognitive domains),**** and

• Not sufficient to significantly impair functional abilities or independence, such that criteria for dementia are NOT met

^*Mixed dementias have overlapping clinical features and more than one pathologic diagnosis.

^**Other less common neurodegenerative and other diseases are not listed that can be identified during life include: vascular dementia, Parkinson disease, Huntington disease, progressive supranuclear palsy, corticobasal degeneration, multiple system atrophy, Creutzfeldt-Jakob disease, and others; in younger people, consider acute conditions (e.g., motor vehicle accident or war-related traumatic brain injury), chronic traumatic encephalopathy (e.g., repetitive sports-related head injuries), and multiple sclerosis. Note that for some neurodegenerative diseases causing dementia in older people, there are currently no means to make the diagnosis during life, such as for Transactive response DNA-binding Protein 43 (TDP-43) form of frontotemporal dementia and for hippocampal sclerosis.

^***Some data suggest this condition is a common cause of dementia in young-onset cases (onset before age 65 years).¹¹⁴

^****Amnestic MCI is defined by neuropsychological test proven impairment in the memory domain, and can be “single domain amnestic MCI” or “multi-domain amnestic MCI”; non-amnestic MCI is defined by impairment in one or more cognitive domains other than memory (such as language, executive function, and/or attention), but not in the memory domain, and can be “single domain non-amnestic MCI” or “multi-domain non-amnestic MCI”.