Using a drug commonly employed to detect cataracts during eye examinations, Harvard researchers have devised an inexpensive new test for Alzheimer's disease that promises to speed the identification of the hard-to-diagnose disorder.
Alzheimer's, which causes loss of memory and bodily control and is eventually fatal, affects as many as 4 million Americans -- including former President Ronald Reagan, who announced Saturday that he is in the early stages of the disease.
Researchers are enthusiastic about the new technique, whose discovery is reported today in the journal Science, but they caution that it has been studied in only a small number of people and must be tested further.
That caution, some experts argue, is justified. At least three other highly touted tests for the disorder failed to live up to their preliminary promise when tested in larger trials.
Neurologists are desperate for a simple way to diagnose Alzheimer's in its earliest stages or before symptoms appear. They believe several new drugs now in development could delay the progression of the disorder if they were given early enough.
"While this is certainly an exciting finding, we have to do more research to confirm these results and see if the test is reliable for Alzheimer's disease," said Dr. Steven DeKosky of the University of Pittsburgh, a member of the Alzheimer's Association advisory board.
Neuroscientists Leonard F. M. Scinto and Huntington Potter of Harvard Medical School got the idea for the test from Dr. Potter's work with Down syndrome, whose victims share many symptoms and biological problems with Alzheimer's patients. Down patients who survive past the age of 30 develop brain lesions virtually identical to those of Alzheimer's patients and also display most of the characteristic mental problems.
Down patients are known to be unusually sensitive to a class of drugs that inhibit the transmission of signals between brain cells by a neurotransmitter called acetylcholine. This hypersensitivity is indicated by a change in heart rate or an increase in pupil size after the administration of such drugs. However, the response of Alzheimer's patients to these drugs apparently had never been studied.
Dr. Scinto's team used the drug tropicamide, settling on a dose 1/100th of that used to dilate pupils during eye examinations. They found that placing a drop of this solution in the eye caused the pupils of Alzheimer's patients to dilate by 13 percent or more within 30 minutes, while those of healthy individuals dilated an average of only 4 percent. The dilation disappears within an hour or two.
They examined 58 elderly individuals, including 19 with early symptoms or a formal diagnosis of Alzheimer's. Eighteen of the 19 showed the dilation. One of those had no obvious mental problems and only a mild difficulty with daily living activities. Within nine months, however, he had developed marked cognitive problems and memory loss, indicating that the test may be able to diagnose Alzheimer's very early in the course of the disease.
Among the remaining healthy patients, only two showed a positive response to the test. Their progress is being monitored.
The researchers said that hundreds, perhaps thousands, of other subjects need to be tested before they can gain confidence in the test's ability to detect the disease.