In 2011 the National Institute on Aging and the Alzheimer’s Association (NIA/AA) issued updated criteria and guidelines for the staging of Alzheimer’s disease. Staging is an attempt to define the severity of a disease and understand its progression. Staging is not a diagnosis.
The NIA/AA guidelines describe Alzheimer’s disease as occurring along a continuum, starting with healthy aging, then progressing to:
The NIA/AA guidelines also recognize for the first time the importance of biomarkers in identifying very early brain changes. Biomarkers are changes in sensory and cognitive abilities or substances in blood, cerebrospinal fluid, or urine. Biomarkers can indicate exposure to a substance, the presence of a disease, or disease progression over time (Lobello et al., 2012).
Magnetic resonance imaging (MRI), positron emission tomography (PET), amyloid imaging, and cerebrospinal fluid analysis are potential biomarkers and may aid in the identification of abnormal brain changes well before symptoms appear. These techniques are only useful, however, when large numbers of people are screened long before symptoms appear, which is currently impractical and even controversial.
Preclinical Alzheimer’s disease is the stage in which pathologic changes have begun to appear in the brain but no cognitive or emotional symptoms are present. During the preclinical stage—currently used only in the research setting—amyloid buildup can be detected in some people using positron emission tomography (PET) scans and cerebrospinal fluid (CSF) analysis. It is unknown what the risk for progression to Alzheimer’s dementia is for these individuals. These biomarkers are still being developed and standardized and are not ready for use by clinicians in general practice (NIA, 2011).
Mild cognitive impairment (MCI) is identified in the NIA/AA guidelines as the next stage of Alzheimer’s disease progression. It is fairly common in older adults and does not necessarily indicate the presence of AD. It is characterized by a decline in cognitive function that falls between the changes associated with typical aging and changes associated with dementia (Lee et al., 2014).
The NIA/AA guidelines for mild cognitive impairment are largely for research, although they clarify existing guidelines for use in a clinical setting. The MCI stage is marked by symptoms of memory problems—enough to be noticed and measured—but not compromising a person’s independence. People with MCI may or may not progress to Alzheimer’s dementia (NIH, 2011).
Although mild cognitive impairment has been described as a transitional stage between normal cognitive aging and dementia, particularly Alzheimer’s disease, community-based studies suggest that many individuals diagnosed with MCI do not progress to Alzheimer’s disease and may even revert to normal. Nevertheless, receiving a diagnosis of mild cognitive impairment can be traumatic and it is important for clinicians to be able to provide their patients with information regarding the likelihood of progression to Alzheimer’s disease (Lee et al., 2014).
The onset of dementia due to Alzheimer’s disease is the third stage described in the NIA/AA guidelines and marks a period in which symptoms become more obvious and independent living becomes more difficult. This stage is referred to as the “dementia phase.”