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Mental lapses, daytime sleepiness may be factors to consider when diagnosing Alzheimer's disease

Cognitive fluctuations are common in people who have dementia with Lewy bodies, but they have rarely been assessed in people with Alzheimer's disease. According to one new study, such fluctuations do occur with Alzheimer's disease and are correlated with impaired performance on neuropsychological tests.

The study found that older people with “cognitive fluctuations”—spontaneous changes in cognition, attention, and arousal—are more likely than people without these fluctuations to have Alzheimer's disease, according to researchers at the Alzheimer's Disease Research Center at Washington University, St. Louis. Of 511 subjects (average age, 78 years) in this NIA-funded study, 12 percent had cognitive fluctuations, defined as having three or four of the following symptoms: often feeling drowsy or lethargic during the day despite a good night's sleep, sleeping 2 or more hours before 7 p.m., having disorganized or unclear thoughts at times, and staring into space for long periods. Subjects with these symptoms were 4.6 times more likely to have Alzheimer's than were those without them, with disorganized, illogical thinking having the strongest correlation with dementia.

These fluctuations may be possible new symptoms to be considered in the diagnosis of Alzheimer's disease, the study authors conclude.

Escandon, A., et al. Effect of cognitive fluctuation on neuropsychological performance in aging and dementia. Neurology. 2010. 74:210-17.