"Clearly patients with mild cognitive impairment compose a heterogeneous group, of whom not all rapidly convert to dementia," said the authors.
"As such, it is important to identify risk factors for progressing rapidly among individuals diagnosed with mild cognitive impairment," he added.
During the study, Dr. Sarah Tomaszewski Farias, of the University of California, Davis, and colleagues studied 111 individuals with mild cognitive impairment.
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.
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 added.
The study appears in Archives of Neurology, one of the JAMA/Archives journals.