Experts have claimed that cognitive fluctuations are more likely to occur in older adults who are developing Alzheimer's disease than in their healthy peers.
Scientists at Washington University School of Medicine in St. Louis said cognitive fluctuations include excessive daytime sleepiness, staring into space and disorganized or illogical thinking.
Until now, little information existed on the potential for links between Alzheimer's and such lapses.
Instead, researchers had associated cognitive fluctuations with another form of dementia called dementia with Lewy bodies.
Senior author James Galvin, M.D., a Washington University neurologist at Barnes-Jewish Hospital, said: "If you have these lapses, they don't by themselves mean that you have Alzheimer's. Such lapses do occur in healthy older adults. But our results suggest that they are something your doctor needs to consider if he or she is evaluating you for problems with thinking and memory."
The experts read Alzheimer's disease evaluations of 511 older adults with memory problems.
Researchers gave participants standard tests of thinking and memory skills. They also interviewed participants and a family member, checking for prolonged daytime sleepiness, drowsiness or lethargy in spite of sufficient sleep the night before, periods of disorganized or illogical thinking, or instances of staring into space for long periods of time.
A total of 12 percent of the participants had at least three of these symptoms, meeting the criteria for cognitive fluctuations.
Those with mental lapses were 4.6 times more likely to be diagnosed with Alzheimer's.
Galvin said: "We have some ideas about why the biology of dementia with Lewy bodies causes these mental lapses, but nothing comparable for Alzheimer's.
"It's possible that some of the patients who were diagnosed with Alzheimer's disease in this study will go on to develop dementia with Lewy bodies, but at the time of the study, they weren't showing any of the Lewy body dementia's core features."
The study has been published in the Jan. 19 issue of Neurology.