Subjective Cognitive Decline, Mild Cognitive Impairment, and Dementia

A Three-Step Approach

In approaching the diagnosis of the diseases that cause dementia, we suggest three steps: (1) determining if subjective cognitive decline, mild cognitive impairment, or dementia is present; (2) determining which clinical syndrome is present; and (3) determining the disease or diseases that are the cause. This strategy expands upon the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) ( ) and is consistent with the current National Institute on Aging and Alzheimer’s Association (NIA-AA) Research Framework ( ). Before delving into each of these steps, it will be useful to have a brief discussion of the spectrum of memory changes, both normal and pathological, that can accompany the aging process.

The Spectrum of Cognitive Changes

When we discuss the results of a memory evaluation with a patient and family, we often begin with a discussion of the spectrum of memory and other cognitive changes in aging ( Fig. 3.1 ). We note that thinking and memory change just as other abilities do as people age (“Can you run as fast as you could at age 30?” “Can you still carry heavy boxes of books?”). In general, these age-associated memory changes—those that are part of the typical aging process—are characterized by some reduction in the ability to learn and remember new material (that is, mild changes in recent or short-term memory), as well as difficulty coming up with names of people and places. These changes, although occasionally embarrassing, are generally not considered to be pathological, but rather part of the normal aging process (“senior moments” is one phrase we commonly hear). On the other end of the spectrum are memory deficits that are clearly caused by dementing disorders such as Alzheimer’s disease. These changes are not part of normal aging, but rather are as a result of a disease process. As a disease process, there is a different continuum that is observed with a different trajectory (see Fig. 3.1 ). In any disease process leading to dementia there must be a preclinical phase when it is just starting and no changes are noticeable, a frank dementia stage when functional impairment is prominent, and an in-between stage when mild changes in memory are observed and cognitive testing may be abnormal. With this as a backdrop, we begin our evaluation of each patient by determining into which categories they fall: cognitively unimpaired/age-associated memory changes, subjective cognitive decline, mild cognitive impairment, or dementia.

Is Dementia Present?

The first distinction that we endeavor to make is whether the patient meets the criteria for dementia. Dementia is not a disease, but simply a term used to signify the loss of cognitive and functional abilities. Determining that dementia is present requires evaluation of 3 areas: (1) cognition, (2) function, and (3) mood and behavior. These areas are typically evaluated by a combination of interviews with the patient, family (and/or other knowledgeable informant), and neuropsychological testing and questionnaires (see Chapter 2 ). Below are the criteria for dementia in DSM-5 (where dementia is referred to as a “major neurocognitive disorder”; Box 3.1 ; see Table 2.2 in Chapter 2 for details on the cognitive domains), and from the National Institute on Aging—Alzheimer’s Association workgroup (where dementia from any cause is called “all-cause dementia”; Box 3.2 ).

As can be seen, the criteria are quite similar, and both include (1) significant cognitive decline as reported by the patient, a knowledgeable informant, or observed by the clinician and (2) documented by formal or informal neuropsychological testing, (3) that the cognitive impairment is sufficient to interfere with independence in everyday activities, and (4) the cognitive impairments are not better explained by delirium or a major psychiatric disorder.