Reports about the prevalence of Alzheimer’s disease seem almost as inexorable as the illness. Each new survey appears to uncover a higher incidence of this wasting affliction of the mind. One reason is the difficulty of diagnosis. Since there is no perfect test for the disease — except upon autopsy — doctors’ estimates of who does or does not have it must rely on subjective assessments. As these methods improve, the number of people with the disease appears to increase. In perhaps the most authoritative survey to date, scientists say Alzheimer’s may be up to twice as common as was previously thought. A study published last week in the Journal of the American Medical Association found that as many as one in ten people over 65 and, astonishingly, nearly half of those over 85 may have the disease. That would raise the number of Americans thought to be afflicted from 2.5 million to 4 million. “I was astounded,” said Dr. Eric Larson of the University of Washington, who wrote an accompanying editorial. “Still, as with any startling finding, it needs to be confirmed.” The study, conducted by a group from Harvard Medical School, examined 3,623 elderly residents in East Boston. With a variety of neurological and cognitive tests, including exams of short-term memory and attention span, the team diagnosed “probable” Alzheimer’s for 3% of those aged 65 to 74, 19% of the 75- to 84-year-olds and 47% of those 85 or older. The project was hailed as one of the first large surveys to go out into an ordinary community, as opposed to examining select populations in clinics or nursing homes. Some previous studies that did look at a community based their diagnoses on existing medical records, which are less reliable. By doing their own testing, the Harvard researchers may have picked up previously unrecognized cases. Still, the latest study is hardly the last word. The complex testing could only confirm the probability of Alzheimer’s, not provide a definite diagnosis. In addition, many of the older residents of East Boston do not speak English as a first language, and had less than three years of schooling; this, says Larson, could have brought down their test scores. The exams may also have failed to take into account the normal decline in mental acuity that comes with aging. Asks Dr. Leonard Kurland of the Mayo Clinic: “Where do you draw the line and say this is normal and this is not?” Nonetheless, one implication of the study is very clear — and frightening: since people 85 or older make up the fastest-growing segment of the population, Alzheimer’s could have devastating consequences for the country’s already strained health-care system.
