Abstract
Alzheimer's disease (AD) can be identified prior to the occurrence of dementia by using biomarkers. Three phases of AD are recognized: an asymptomatic biomarker-positive phase, a phase with positive biomarkers and mild cognitive deficits, and a dementia phase. Codification of these phases was first accomplished in 2007 by an International Work Group (IWG) led by Bruno Dubois. The definitions relevant to the approach were further clarified in 2010. In 2011, the National Institute on Aging/Alzheimer's Association (NIA/AA) established three work groups to develop definitions and criteria for these three phases of AD. The criteria of the IWG and those of the NIA/AA have many similarities and important differences. The two sets of criteria concur in recognizing the onset of AD prior to dementia. The three phases of AD described in both sets of criteria embrace the same clinical entities but with different terminologies and emphases. IWG criteria emphasize a single clinico-biological approach that includes all symptomatic phases of AD and uses the same diagnostic framework across the spectrum of symptomatic disease; the NIA/AA criteria apply different diagnostic approaches to the three phases. Biomarkers are an integrated and required part of the IWG criteria and are optional in the NIA/AA approach. Both sets of criteria have substantial strengths, but new information demonstrates shortcomings that can be addressed in future revisions of the criteria. These new criteria have profound implications, including greatly increasing the number of people identified as suffering from AD and increasing the time that patients will spend with knowledge of the presence of the disease.
Highlights
Alzheimer’s disease (AD) can be identified prior to the occurrence of dementia by using biomarkers
Alzheimer’s disease (AD) has traditionally been defined as a type of dementia, and criteria have been provided by the National Institute of Neurological and Communicative Disorders and Stroke – Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA) [1], the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) [2], and the 10th revision of the International Classification of Diseases (ICD-10) [3]
There were several notable aspects of these criteria: (a) patients had to have cognitive deficits and functional compromise severe enough to meet criteria for dementia, (b) a confirmed diagnosis depended on postmortem examination, (c) the most accurate diagnosis that the clinician could make for the living patient was ‘probable AD’, (d) other possible causes of cognitive impairment had to be excluded by the clinician, and (e) the cognitive deficits were not operationalized for characteristics or severity
Summary
Alzheimer’s disease (AD) can be identified prior to the occurrence of dementia by using biomarkers. The IWG criteria do not offer any nomenclature for the general nonspecific syndrome of ‘MCI’ in favor of developing criteria that use biomarkers to identify that subset of MCI patients who are in the predementia phase of AD.
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