The study of neuroscience over the last three or more decades has revealed a greater understanding of how our brain works and of what causes dementia including Alzheimer’s disease. Yet the clinical diagnostic guidelines for determining what constitutes Alzheimer’s, have only just been revised after a time span of 27 years.
This update now covers the full spectrum, from the earliest preclinical stages, through mild cognitive impairment, to dementia due to Alzheimer’s pathology.
The guidelines also address for the first time the use of imaging and biochemical markers in blood and spinal fluid to help determine whether changes present are likely to be due to Alzheimer’s. As yet biochemical markers and scans are not being used in the clinical setting, they are still predominantly research tools. However this is likely to be changing in the not too distant future.
One of the key drivers to the updated guidelines has been the need to find good clinical tools to permit early and accurate diagnosis.
Previously Alzheimer’s could only be confirmed following death. Autopsy was used to show the pathological findings of amyloid plaques. We now know that in Alzheimer’s disease, changes in the brain start developing long before any clinical symptoms are apparent and the symptoms do not always correlate to abnormal findings in the brain.
The National Institute on Aging/Alzheimer’s Association Diagnostic Guidelines for Alzheimer’s disease now covers three distinct stages of Alzheimer’s.
1 The Preclinical Stage.
These guidelines only apply currently to a research setting. In the preclinical stage, brain changes are starting to develop, including accumulation of amyloid and some other nerve cell changes. Significant clinical symptoms are not apparent at this stage. PET scan and CSF analysis may detect the amyloid build up in some people. It remains unknown what the risk of progression of to Alzheimer’s is from this. There is much research continuing into the potential use of biomarkers in a clinical setting.
2 Mild Cognitive Impairment.
These guidelines are also mostly for research. Here a person is recognised to be suffering from memory problems but not in such a way to be impairing their daily functioning. Not everyone with MCI will progress to full blown Alzheimer’s disease. The use of biomarkers here, is looking for evidence of increased tau protein or decreased levels of beta amyloid in the CSF, reduced glucose uptake in the brain (shown on PET scan) and atrophy of certain parts of the brain (using MRI scans)
3 Alzheimer’s dementia.
Here the clinical manifestations include (in addition to memory loss,) decline in word finding, visuo-spatial difficulty and impaired reasoning or judgement (higher levels of cognition). Biomarker tested here can be used to increase or decrease the level of certainty about a diagnosis and to differentiate the dementia of Alzheimer’s from other forms of dementia.
This new framework will allow for new findings to be incorporated as discovered. So fortunately, we are unlikely to have to wait for another 27 years before any further revision occurs.
Ref: NIH/National Institute on Ageing. April 19, 2011 in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.