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Improving Alzheimer's Diagnosis

Proposal: Use High-Tech Alzheimer's Tests for Earlier Diagnosis
By
WebMD Health News
Reviewed by Louise Chang, MD

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 this."

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 fluid
  • A PET scan showing patterns of brain activity linked to Alzheimer's disease
  • 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 Alzheimer's disease.

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, targeted therapy."

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