July 13, 2010 -- HONOLULU -- Tests involving brain imaging and screening proteins find in the in cerebrospinal fluid (CSF) can now be used clinically in diagnosing Alzheimer's disease, according to new guidelines proposed by a working group from the National Institute on Aging and the Alzheimer's Association.
If adopted, the guidelines would be the first major update in diagnostic criteria for Alzheimer's disease since 1984.
The working group, chaired by Dr. Guy McKhann of Johns Hopkins University in Baltimore, presented its proposal here at the International Conference on Alzheimer's Disease (ICAD), seeking the first outside comment from the medical community.
The proposal said "probable Alzheimer's disease" can be diagnosed in patients with clinical dementia in the absence of a documented long-term decline in cognitive function if the results of any of five specific imaging or CSF tests are positive.
The proposed guideline would still reserve a definitive diagnosis for patients after they died, on the basis of autopsy findings.
Previously, diagnosis of probable Alzheimer's disease was based solely on clinical presentation, with other potential causes of dementia such as cerebrovascular or Parkinson's disease ruled out. It also established age cutoffs and implied a requirement for extensive neuropsychological testing.
"These criteria have some shortcomings that need to be addressed," the working group wrote in its report. "Some relate to lack of knowledge at the time of the development of the original criteria. Others relate to the vast expansion of our knowledge of the biology of [Alzheimer's disease]."
Besides the new science on biomarkers and imaging of brain abnormalities, other advances include better ways to distinguish dementias with different causes. And it is now understood that memory impairment is not "always the primary cognitive deficit in all patients" with Alzheimer's disease, the working group indicated.
But one prominent Alzheimer's disease researcher contacted by MedPage Today and ABC News called the inclusion of imaging and biomarker data in diagnosis at this point "a step in the wrong direction."
Dr. Peter Whitehouse of Case Western Reserve University in Cleveland, said that the CSF and imaging tests "add expense and are poorly validated, in my view."
Others shared these concerns but indicated that the addition of these tests to the diagnostic toolkit would still be beneficial on balance.
"These new tests may help us make an earlier diagnosis and thereby gives us a greater window of time in which to help maximize the patient's ability to fight the disease," said Dr. Murali Doraiswamy of Duke University.
But he suggested that the criteria need field testing before clinicians adopt them.
"There could be substantive increase in costs to society and Medicare if doctors game the system and make every patient with memory problems undergo multiple brain scans or spinal taps," Doraiswamy warned.
Dr. Kostas Lyketsos of Johns Hopkins, pointed out that the tests were expensive, and hence their clinical uptake would correspond to the extent to which Medicare and other insurers will pay for them.
If they do become widely available in practice, the number of patients receiving Alzheimer's diagnoses will soar, Lyketsos predicted.
"I expect that the increase related to the sheer number of people being worked up with these tests, simply driven by their availability, will significantly outnumber the group [with non-Alzheimer dementias] being 'ruled out.' It will not change the number of people with the disease or the dementia, but it will increase the number being diagnosed," he said.