Spinal Fluid, Imaging Tests Still Experimental but May Confirm Early Alzheimer's
By Daniel J. DeNoon
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Reviewed by Laura J. Martin, MD
It's been 27 years since guidelines for diagnosing Alzheimer's disease were laid out. Since 1984, research has shown Alzheimer's to be a disease that begins decades before dementia appears.
Now panels from the National Institute on Aging and the Alzheimer's Association have split Alzheimer's disease into three stages:
- Dementia, including mental impairments not as severe as those previously required for an Alzheimer's diagnosis.
- Mild cognitive impairment due to Alzheimer's disease. This new category of Alzheimer's disease includes patients with changes in memory and thinking ability that do not keep them from performing everyday functions, but which strongly suggest that a patient will develop Alzheimer's dementia.
- Preclinical Alzheimer's disease. The new guidelines recognize that the Alzheimer's disease process begins before there are any symptoms. But for now, there aren't good enough tests to tell whether a person has this stage of Alzheimer's.
Perhaps the biggest change is the way doctors will diagnose Alzheimer's dementia, says Gary Kennedy, MD. Kennedy, a geriatric psychiatrist who specializes in treating patients with Alzheimer's disease at Montefiore Medical Center in New York, was not a member of the guideline-writing committees.
"The real new component here is you need not have memory impairment to have Alzheimer's dementia. They are ratcheting down the dementia criteria," Kennedy tells WebMD. "If you're having trouble making plans, have problems adapting to changes in your environment, or have lapses that impair your social involvement with others, you may have Alzheimer's disease even if your memory is not so bad."
Diagnosis of Early Alzheimer's Disease
Also new is that the guidelines assume it is possible to identify people with mild cognitive impairment whose worsening symptoms likely reflect an early stage of Alzheimer's disease.
The criteria for diagnosing mild cognitive impairment due to Alzheimer's disease are:
- Concern expressed by a patient, family member, friend, or doctor, about a change in mental function: specifically, memory, reasoning/problem solving, language ability, visual/spatial skills, or ability to pay attention.
- Objective evidence, usually test results, showing that a patient has one or more of these changes in mental function.
- The person is still independent and able to carry out everyday functions.
- The person is not demented.
"'Mild' here means you are not socially impaired, but it does imply you know there is a problem, and your family and friends notice a problem," Kennedy says.
The problem, of course, is that many people with mild cognitive impairment deny there is a problem.
"So the criteria need refinement," Kennedy says. "This is more of a provisional diagnosis. That is why the guidelines put an emphasis on biomarkers -- signposts that dementia may be down the road."
Biomarkers for Alzheimer's Disease
Biomarkers are being developed for Alzheimer's disease, but the guidelines stress that they are not yet ready for clinical use except in certain well-defined situations.
There are several Alzheimer's biomarkers being explored, but two basic types are in the most advanced stages of development:
- Cerebrospinal fluid (CSF) test. A protein called beta-amyloid begins to accumulate in the brain even in the early stages of Alzheimer's disease. When this happens, beta-amyloid levels drop in the CSF. Tests of CSF, collected by a spinal tap, measure beta-amyloid levels.
- Imaging tests such as PET scans, SPECT perfusion imaging, and even MRI scans can detect beta-amyloid accumulation or markers of brain injury typical of Alzheimer's disease.
The new guidelines stress that none of these tests have been fully validated and that there are no cutoff levels that clearly distinguish normal people from those who have Alzheimer's.
Nevertheless, the guidelines suggest that for some patients with mild cognitive impairment suggestive of Alzheimer's disease, biomarker tests "would affect levels of certainty in the diagnosis."
Treatment for Alzheimer's Disease
There's no cure for Alzheimer's disease, so why the emphasis on early detection? Kennedy says the earlier you detect possible Alzheimer's, the more you can do about it.
"Ten years ago we said there was no treatment for Alzheimer's. That isn't true now," he says. "We can't cure it, but just like diabetes, we can delay the illness and disability associated with it. I counsel patients to be aggressive about diet and exercise, to take the medications they need for other conditions, and to stay intellectually engaged."
The new Alzheimer's guidelines appear in the April 19 online issue of Alzheimer's & Dementia: The Journal of the Alzheimer's Association.
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