"With the introduction of promising new drugs to treat the mildest stages of Alzheimer's disease, diagnosing patients early is more important than ever before," said Dr. Dan Silverman, principal investigator, UCLA assistant professor of molecular and medical pharmacology and associate director of imaging for the UCLA Alzheimer's Disease Center.
"PET boosts the number of Alzheimer's cases that are detected early and can substantially reduce the number of elderly patients falsely diagnosed with Alzheimer's disease," he said.
Silverman and his colleagues modeled the value of two diagnostic strategies for evaluating whether Alzheimer's disease was responsible for early signs of dementia in elderly patients.
The first approach followed the American Academy of Neurology (AAN) 2001 recommendations for clinical evaluation of dementia.
The second approach followed the AAN recommendations, but also incorporated PET to measure the patient's brain metabolic pattern for evidence of early Alzheimer-type damage.
Patients in both groups were then treated according to the AAN 2001 recommendations for management of dementia.
Silverman and his associates studied both strategies for their range of accuracy in diagnosing Alzheimer's disease. The differences proved dramatic.
"Although both approaches accurately diagnosed most Alzheimer's patients, we found that the appropriate use of PET could reduce erroneous diagnoses by half," Silverman said.
The UCLA team examined the best current medical literature endorsed by the AAN on Alzheimer's diagnosis. For every 100 patients suffering early cognitive decline, the literature showed that conventional methods would have falsely attributed the patients' symptoms to early Alzheimer's disease in 23 cases, and overlooked eight cases of Alzheimer's.
Silverman's team then used clinical benefit-risk analysis to show that incorporating the use of PET in these patients' clinical evaluations would have prevented 11 of the 23 false positives and five of the eight false negatives.
Using these figures, Silverman next calculated how much PET would reduce months of unnecessary nursing-home care.
UCLA researchers knew that early drug therapy typically slows the cognitive decline caused by Alzheimer's disease by nine to 18 months without significantly affecting life expectancy. Multiplying by a conservative value of nine months, Silverman estimated that accurate identification of Alzheimer's disease in 5 percent more people would diminish institutionalization by at least 45 months for every 100 patients.
In the 11 per 100 people spared from a false diagnosis with Alzheimer's disease, Silverman and his colleagues estimated that adding PET to the patients' clinical evaluations would prevent more than 130 months per year of needless drug therapy per 100 people.
Although effective when taken properly, drugs to postpone Alzheimer's disease are costly and can cause significant gastrointestinal side effects, such as nausea, vomiting and diarrhea.
Overall, the benefit of introducing PET into dementia patients' assessments corresponded to a 62 percent decrease in avoidable months of nursing-home care and a 48 percent drop in unnecessary drug treatment.
"It's worse to diagnose someone with Alzheimer's later than earlier, because we now have drugs available to help delay progression of the disease," Silverman said. "Postponing drug therapy by as little as six months in people with Alzheimer's may have long-term consequences for their cognitive function."
At least 30 percent of people 85 and older suffer from Alzheimer's disease, the most common form of dementia. The disease exacts an enormous financial burden on families and society. In the United States alone, more than $90 billion will be spent on Alzheimer's-related expenses each year, according to the National Institute for Aging.