People with mild cognitive impairment, or MCI, have cognitive deficits that are more pronounced than is typical for their age group, but less severe than those with Alzheimer's dementia. While MCI can be a precursor to Alzheimer's disease, it is unclear how many people with MCI will go on to develop dementia.
To address this question, University of Pittsburgh researchers led a study involving nearly 2,000 volunteers age 65 or older living in a western Pennsylvania community (Ganguli et al., 2011). They found that only a small proportion of those who met the diagnostic criteria for MCI progressed to dementia over the course of 1 year; the majority remained stable, and a few even improved.
These results differ from previous findings in clinical research settings, perhaps because people who seek clinical diagnosis and care for MCI (either on their own or at the behest of family members) may already be on the way to developing dementia. MCI in the general community may spring from a greater variety of causes that can be treated or managed, such as depression or side effects from medications. The study also showed that MCI is more likely to progress to dementia when a person has specific memory impairment and/or more than one impaired cognitive domain.
Alzheimer's disease has a long prodromal phase, during which people begin to experience cognitive changes that herald the onset of the more severe stages of the disorder. To better understand this early stage, researchers at Rush University Medical Center, Chicago, followed for up to 16 years more than 2,000 older volunteers participating in two ongoing studies, the Religious Orders Study and the Rush Memory and Aging Project (Wilson et al., 2011).
They found that the 462 volunteers who eventually developed Alzheimer's showed accelerated decline in multiple areas of cognitive function (memory, visuospatial skills, and perceptual processing) during the 5 to 6 years before receiving a diagnoses of Alzheimer's disease. In contrast, little evidence of cognitive decline was seen in the larger group of participants who remained free of the disease.
This study suggests that declines in cognitive function are detectable well before the onset of Alzheimer's dementia, and that changes in cognition are not an inevitable consequence of aging. Further, it suggests that treatments, once available, may be most effective if started early-underscoring the need for biological and behavioral markers to aid in early detection.