Among individuals with mild cognitive impairment, often considered a transitional state between normal cognitive function and Alzheimer's dementia, those who have more difficulties performing routine activities appear more likely to progress quickly to dementia, according to a report in the September issue of Archives of Neurology, one of the JAMA/Archives journals.
Mild cognitive impairment is recognized as a risk factor for dementia and an important public health issue, according to background information in the article. "Annual conversion rates [from mild cognitive impairment to dementia] often range from 10 percent to 15 percent in clinic samples. Conversion rates in community-based studies are often substantially lower (i.e., 3.8 percent to 6.3 percent per year)," the authors write. "Clearly patients with mild cognitive impairment compose a heterogeneous group, of whom not all rapidly convert to dementia. As such, it is important to identify risk factors for progressing rapidly among individuals diagnosed with mild cognitive impairment."
Sarah Tomaszewski Farias, Ph.D., of the University of California, Davis, and colleagues studied 111 individuals with mild cognitive impairment. Of these, 46 percent (51) were recruited from patients referred to a university-based memory disorders clinic on suspicion of cognitive decline, and 54 percent (60) were recruited directly through community outreach. All participants underwent annual clinical evaluations, diagnostic imaging, routine laboratory tests and neuropsychological evaluations.
During an average of 2.4 years of follow-up, 28 individuals progressed from mild cognitive impairment to dementia, including 23 from the clinic and five from the community. Annually, 13 percent of the clinic-based group and 3 percent of the community group converted into dementia.
Other than recruitment source, the only factor associated with conversion from mild cognitive impairment to dementia was the degree of functional impairment at the beginning of the study—no demographic, cognitive or neuroimaging variables predicted this progression.
"Thus, regardless of whether an individual was a clinic patient or recruited directly from the community, more functional impairment at baseline was an important risk for future conversion to dementia," the authors write. "The greater functional impairment at baseline within the clinically recruited group appears to account for their increased risk of conversion."
The results suggest that "in an educationally and ethnically diverse population, those with more functional impairment at their baseline evaluation—regardless of whether they are actively seeking an evaluation for a neurodegenerative disease—are at increased risk for conversion to dementia even within a relatively short follow-up period," they conclude.
- Sarah Tomaszewski Farias; Dan Mungas; Bruce R. Reed; Danielle Harvey; Charles DeCarli. Progression of Mild Cognitive Impairment to Dementia in Clinic- vs Community-Based Cohorts. Arch Neurol, 2009; 66 (9): 1151-1157 [link]
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