The incidence of MCI differs by subtype and is higher in men: the Mayo Clinic Study of Aging

Abstract

Objective: Although incidence rates for mild cognitive impairment (MCI) have been reported, few studies were specifically designed to measure the incidence of MCI and its subtypes using published criteria. We estimated the incidence of amnestic MCI (aMCI) and nonamnestic MCI (naMCI) in men and women separately.

Methods: A population-based prospective cohort of Olmsted County, MN, residents ages 70-89 years on October 1, 2004, underwent baseline and 15-month interval evaluations that included the Clinical Dementia Rating scale, a neurologic evaluation, and neuropsychological testing. A panel of examiners blinded to previous diagnoses reviewed data at each serial evaluation to assess cognitive status according to published criteria.

Results: Among 1,450 subjects who were cognitively normal at baseline, 296 developed MCI. The age- and sex-standardized incidence rate of MCI was 63.6 (per 1,000 person-years) overall, and was higher in men (72.4) than women (57.3) and for aMCI (37.7) than naMCI (14.7). The incidence rate of aMCI was higher for men (43.9) than women (33.3), and for subjects with ≤12 years of education (42.6) than higher education (32.5). The risk of naMCI was also higher for men (20.0) than women (10.9) and for subjects with ≤12 years of education (20.3) than higher education (10.2).

Conclusions: The incidence rates for MCI are substantial. Differences in incidence rates by clinical subtype and by sex suggest that risk factors for MCI should be investigated separately for aMCI and naMCI, and in men and women.

Figure 1. Study flow chart

*These percentages refer to a total of 1,450 (100.0%) subjects included in the primary analyses. aMCI = amnestic mild cognitive impairment; MCI = mild cognitive impairment; naMCI = nonamnestic mild cognitive impairment; TICS-m = Telephone Interview of Cognitive Status–modified.

Figure 2. Incidence rates of mild cognitive impairment (MCI) in Olmsted County, MN

(A) Age- and sex-specific incidence rates of MCI. (B) Education- and sex-specific incidence rates of MCI. (C) Age- and type-specific incidence rates of MCI. (D) Education- and type-specific incidence rates of MCI. aMCI = amnestic mild cognitive impairment; MD = multiple-domain; naMCI = nonamnestic mild cognitive impairment; SD = single-domain.

Figure 3. Comparison of age- and sex-specific incidence rates for mild cognitive impairment (MCI) across studies

(A) Incidence rates for any MCI. (B) Incidence rates for amnestic mild cognitive impairment (aMCI). (C) Incidence rates for nonamnestic mild cognitive impairment (naMCI). The dashed lines represent rates for women (W), and the solid lines represent rates for men (M). The red lines represent the Leipzig Longitudinal Study of the Aged from Germany (D); the black lines represent the Mayo Clinic Study of Aging from the United States, present study (US); the blue lines represent the Kungsholmen Project from Sweden (S). For the Swedish study, we considered their definition of “other cognitive impairment no dementia” as equivalent to naMCI.