Improving Alzheimer's Diagnosis
Proposal: Use High-Tech Alzheimer's Tests for Earlier Diagnosis
July 9, 2007 -- It's time to change the way doctors diagnose Alzheimer's
disease, says an international panel of experts.
Despite more than two decades of scientific advances in understanding
Alzheimer's disease, doctors are still stuck in 1984. That's when a U.S.
National Institutes of Health working group came up with the clinical criteria
for a formal diagnosis of Alzheimer's disease.
It's time for radical change, argue Bruno Dubois, MD, of Salpêtrière
Hospital, Paris, and 18 other leading Alzheimer's experts.
The old criteria "have now fallen behind the unprecedented growth of
scientific knowledge," Dubois and colleagues write in the August issue of
The Lancet Neurology.
That's true, says Norman Foster, MD, director of the Center for Alzheimer's
Care, Imaging, and Research at the University of Utah, Salt Lake City. Foster's
editorial accompanies the paper by Dubois and colleagues.
"We now are seeing the potential to disrupt the basic development of
Alzheimer's disease with medications," Foster tells WebMD. "So we want
early diagnosis and early intervention. The current criteria get in the way of
High-Tech Alzheimer's Diagnosis
People are said to have probable Alzheimer's disease if they have two
clinical signs: a memory disorder and impairment of at least one other mental
function. For an Alzheimer's diagnosis, both these problems must interfere with
social function or the activities of daily living.
That was a big breakthrough 25 years ago. Since then, doctors have learned
that several other conditions cause the same impairments. Yet with an emphasis
on earlier treatment, there's pressure on doctors to diagnose Alzheimer's
disease as early as possible.
"We are caught between a rock and a hard place as clinicians,"
Foster says. "We cannot distinguish accurately when mild cognitive
impairment represents Alzheimer's disease, when it represents some other
significant illness, or when it is just a passing problem."
Dubois and colleagues propose using a new formula. To get an Alzheimer's
diagnosis, a person would first have to suffer memory loss that gets worse over
a six-month period. That person would also have to have at least one physical
"biomarker" of Alzheimer's disease:
- An MRI scan showing shrinking of a particular part of the brain
- Abnormal proteins -- beta-amyloid or tau tangles -- in the cerebrospinal
- A PET scan showing patterns of brain activity linked to Alzheimer's
- A genetic mutation linked to Alzheimer's disease
These are expensive, high-tech tests. All have yet to be "validated"
-- that is, proven to detect Alzheimer's disease within specified limits.
Foster says the most promising of these high-tech Alzheimer's tests is
already in use: genetic testing for an Alzheimer's gene. However, only a small
percentage of Alzheimer's patients carry the genetic mutations known to cause
The next most promising of these tests, Foster says, is a PET scan for
deposits of amyloid protein in the brain. Today, those deposits very likely
mean Alzheimer's if a person already has symptoms. It's still unclear what
these deposits mean for people who do not have symptoms.
Finally, Foster says that looking for amyloid or tau proteins in the
cerebrospinal fluid holds great promise. But it's not yet clear how often these
proteins predict Alzheimer's disease.
Dubois and colleagues call for intensive research aimed at validating the
new criteria. Foster strongly agrees.
"Diagnosis is the foundation of effective treatment for Alzheimer's
disease," he says. "When physicians and families just accept terms like
'senility' or 'dementia,' they give up the opportunity for more effective,