Published on: April 5, 2012
by John K. Grandy for JAAPA
The earliest stages of Alzheimer disease (AD) start years, perhaps decades, before the diagnosis of dementia is made.
The new criteria are projected to allow the diagnosis of dementia without access to neuropsychological testing, specialized imaging, neurogenetic testing, or CSF biomarker analysis.
Mild cognitive impairment due to AD is a clinical diagnosis and a cognitive impairment that is not normal for age-associated memory impairment or cognitive decline.
Impaired ability to learn and retain information (episodic memory) is more common in MCI patients who progress to AD dementia than in MCI patients who do not progress to AD dementia.
Alzheimer disease (AD) affects more than 37 million people worldwide and is marked by a slow, progressive neurodegenerative decline that has cognitive and behavioral elements. The National Institute on Aging (NIA) and the Alzheimer’s Association organized more than 40 experts into three work groups to revise and update the guidelines for diagnosing AD. Their work focused on the diagnostic and research criteria as pertinent to the continuum of AD.
These guidelines, published in 2011 as three articles, are the first update since the 1984 criteria published by the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA). The new guidelines amalgamate clinical and research criteria that will ultimately assist clinicians to more accurately identify patients with AD and particular phases of the disease process.
RATIONALE FOR THE UPDATE
In addition to the many advances in clinical science and technology since 1984, several other key reasons necessitated these updates:
The 1984 criteria have a sensitivity and specificity of just 81% and 70%, respectively. The long-standing axiom has been that a definitive diagnosis of AD can only be made neuropathologically, ie, by postmortem biopsy. However, some studies have demonstrated that 20% to 40% of nondemented patients had enough plaques and tangles postmortem to qualify for the diagnosis of AD, although they were asymptomatic prior to death.
The older guidelines did not distinguish AD dementia from other conditions that cause dementia (Table 1). In fact, the original description of the diagnosis of dementia was based on criteria published in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition(DSM III).
The research involving biomarkers and neurogenetics, coupled with their potential to identify patients with presymptomatic AD, has only recently been recognized.
In the 1984 criteria, AD was not recognized as a disease of many stages that culminate with dementia. Breakthroughs in understanding the pathophysiology of AD make clear that the earliest stages of AD start years, perhaps decades, before the diagnosis of dementia is made.
The authors of the 1984 publication themselves anticipated the future need for an update, writing: “The criteria are not yet fully operational because of insufficient knowledge about the disease.”
Among the reasons for the 27-year delay in updating the guidelines are the obstacles that needed to be overcome. These included the lack of validated assessment tools, necessary infrastructure, and systematic clinical and longitudinal studies. Another critical challenge, which remains unresolved even today, is distinguishing the pathologic brain changes that are associated with normal senescence from changes that are associated with AD.
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