Cognitive abilities of older persons range from normal, to mild cognitive impairment,
to dementia. Few large longitudinal studies have compared the natural history of mild
cognitive impairment with similar persons without cognitive impairment.
Participants were older Catholic clergy without dementia, 211 with mild cognitive
impairment and 587 without cognitive impairment, who underwent annual clinical evaluation
for AD and an assessment of different cognitive abilities. Cognitive performance tests
were summarized to yield a composite measure of global cognitive function and separate
summary measures of episodic memory, semantic memory, working memory, perceptual speed,
and visuospatial ability. The authors compared the risk of death, risk of incident
AD, and rates of change in global cognition and different cognitive domains among
persons with mild cognitive impairment to those without cognitive impairment. All
models controlled for age, sex, and education.
On average, persons with mild cognitive impairment had significantly lower scores
at baseline in all cognitive domains. Over an average of 4.5 years of follow-up, 30%
of persons with mild cognitive impairment died, a rate 1.7 times higher than those
without cognitive impairment (95% CI, 1.2 to 2.5). In addition, 64 (34%) persons with
mild cognitive impairment developed AD, a rate 3.1 times higher than those without
cognitive impairment (95% CI, 2.1 to 4.5). Finally, persons with mild cognitive impairment
declined significantly faster on measures of episodic memory, semantic memory, and
perceptual speed, but not on measures of working memory or visuospatial ability, as
compared with persons without cognitive impairment.
Mild cognitive impairment is associated with an increased risk of death and incident
AD, and a greater rate of decline in selected cognitive abilities.