PHILADELPHIA - Advances in imaging technology such as PET scans and MRI could someday help detect Alzheimer's disease years before obvious symptoms emerge, enabling doctors to begin therapy early and determine whether patients are benefiting, scientists told a conference on the brain-wasting disease yesterday.
Until recently, the only sure way to detect the telltale plaques and tangles of Alzheimer's disease was to analyze the brain after the patient had died.
Although doctors can diagnose the disease by testing a patient's memory and listening to caregivers' accounts, the diagnosis is usually made years after the brain has begun to deteriorate.
For the average patient today, early diagnosis might not be useful because there are no proven treatments that significantly alter the course of the disease. Medications approved for use outside clinical trials have only modest effects.
But scientists here at the Ninth International Conference on Alzheimer's Disease and Related Disorders said early detection will become useful once better treatments emerge. Eventually, doctors might try to treat Alzheimer's like cancer - as early as possible, before it's too late to make a difference.
"This is very new - I don't think this is something you're going to go to your doctors and get prescribed to you anytime soon," Dr. William E. Klunk, professor of psychiatry at the University of Pittsburgh, said of the brain scans. But he added, "We want to move the field earlier and earlier and detect the earliest symptoms, even in the pre-Alzheimer's stages."
While Klunk and other scientists are optimistic about the potential of brain scans to advance Alzheimer's prevention and treatment, they warned that companies are advertising expensive PET (positron-emission tomography) scans to people who are worried they might be in the early stages of dementia.
For that purpose, PET scans are experimental, and it might be years before they're ready for widespread use. Medicare does not cover PET scans for Alzheimer's, although the federal government has proposed rules that would allow payment - with tight restrictions on who would be eligible.
"It is not a screening tool - it's not to be used by everyone," said Dr. Gary Small, director of the UCLA Center on Aging. The tests cost about $1,500 per session.
Scientists with the Pittsburgh Alzheimer's Research Center announced this week that they have developed an injectable compound that sticks to the so-called amyloid plaques that accumulate in the brain as long as a decade before Alzheimer's patients experience serious memory loss.
If the plaques are present, the chemical causes the afflicted area to "light up" on images taken by PET scans.
Though it's unclear whether the plaques are the cause or result of Alzheimer's, they're widely regarded as a telltale sign.
The Pittsburgh scientists say the test can detect plaques present in patients suffering from mild cognitive impairment. That's an early stage of Alzheimer's marked by memory loss, but not by other symptoms such as difficulty speaking, recognizing faces or carrying out everyday tasks.
Some of the most promising drugs being tested today are designed to stop or reverse plaque buildup. To determine if the drugs are working, scientists are scanning the brain at intervals to see if the plaques are getting worse, stabilizing or disappearing.
At UCLA, scientists have developed a different compound that sticks to the tangles of abnormal "tau" proteins in the brains of people suffering from frontal temporal dementia, the most common form of dementia after Alzheimer's. Like the Pittsburgh compound, the chemical is used in conjunction with PET scans.
"The new technique may help us better differentiate between Alzheimer's and other forms of dementia - leading to more effective treatments," said Small of UCLA.
Andrew J. Saykin of Dartmouth Medical School said he is using another brain scan technology - magnetic resonance imaging - to detect shrinkage in regions affected by Alzheimer's and to see whether regions involved in reasoning and memory are less active.
In the Dartmouth study, scientists are following 90 volunteers as they age. In clinical evaluations, a third of the volunteers have no problems with memory, while another third suffer from mild cognitive impairment. The rest complained of mild memory loss but scored well on memory tests.