shows characteristics of the 856 ADAMS participants, stratified by cognitive status. The cognitive impairment without dementia group comprised individuals who were well distributed across education levels and age ranges and included 36 participants age 90 years or older. Mean age increased from the normal cognition group to the cognitive impairment without dementia and dementia groups, whereas the mean level of education progressively decreased across these groups. The Mini-Mental State Examination score (19
) progressively declined from the normal cognition group to the cognitive impairment without dementia group to the dementia group, whereas the Dementia Severity Rating Scale (20
) score progressively increased across these groups.
Characteristics of Baseline ADAMS Sample*
shows the frequency and characteristics of the subtypes of cognitive impairment without dementia. Patients with the 4 most frequent subtypes (prodromal Alzheimer disease, medical conditions, stroke, and vascular cognitive impairment without dementia) were similar in age, years of education, Mini-Mental State Examination score, and Dementia Severity Rating Scale score. However, women were more frequent in the medical conditions group than in the 3 other most common subtypes (chi-square, 12.17; P = 0.004).
Frequencies and Estimated Population Characteristics for Cognitive Impairment without Dementia Subtypes*
shows the national prevalence estimates for cognitive impairment without dementia and its more frequent subtypes, stratified by 9- or 10-year age ranges. It also reports the estimated number of individuals with cognitive impairment without dementia in the United States for the same groups. We estimated that 5.4 million people age 71 years or older had cognitive impairment without dementia in 2002, whereas an estimated 2.0 million had prodromal Alzheimer disease. Because of the uncertainty surrounding the diagnostic criteria for cognitive impairment without dementia, we explored how the prevalence estimates for dementia would change if we considered some of those with a diagnosis of cognitive impairment without dementia at the initial assessment to have had dementia at baseline. For these analyses, we considered all individuals who progressed to dementia at the follow-up visit to have had dementia at baseline, whereas all those who progressed to Alzheimer disease were considered to have Alzheimer disease at baseline. Because estimates of the prevalence of cognitive impairment without dementia for persons younger than age 71 years are not available, we used rates of dementia for persons age 60 to 71 years from other studies (32
) and combined them with estimates from this study and our previous research (11
). This resulted in an estimate of almost 4.7 million individuals age 60 years or older with dementia in the United States, up from our previous estimate of 3.8 million, and a total of 3.3 million with Alzheimer disease, up from 2.5 million (11
Estimated National Prevalence of Cognitive Impairment without Dementia, by Age Categories*
In a logistic regression model, cognitive impairment without dementia was more likely in older persons (odds ratio [OR], 1.13 [95% CI, 1.09 to 1.17] per year) and men (OR, 1.62 [CI, 1.09 to 2.41]) and less likely in those with more years of education (OR, 0.89 [CI, 0.84 to 0.94] per year). Among those with prodromal Alzheimer disease, 48.3% had at least 1 APOE ε4 allele, a rate higher than that in the 3 other most common subtypes (chi-square, 12.23; P = 0.007). However, the presence of an APOE ε4 allele was not significantly related in the model to the odds of cognitive impairment, including all subtypes (OR, 1.56 [CI, 0.92 to 2.67]). Race was not significantly associated with cognitive impairment without dementia (OR, 1.29 [CI, 0.66 to 2.54]).
to (available at www.annals.org
) present unweighted values from to , respectively.
Appendix Table 4
Subtypes of Cognitive Impairment without Dementia, by Age Categories (Unweighted)*
We reassessed participants, on average, 17.04 months (SD, 1.62) after their initial assessment. In a logistic regression model, progression from cognitive impairment without dementia to dementia at follow-up was more probable among older individuals (OR, 1.08 [CI, 1.02 to 1.14] per year) and less probable among those with more years of education (OR, 0.88 [CI, 0.81 to 0.96] per year). Men tended to be less likely to progress to dementia (OR, 0.37 [CI, 0.13 to 1.05]). Neither race (OR, 0.46 [CI, 0.16 to 1.27]) nor presence of an APOE ε4 allele (OR, 1.33 [CI, 0.55 to 3.23]) was significantly associated with progression to dementia.
summarizes the outcomes of the follow-up assessments for the most frequent subtypes of cognitive impairment without dementia. On follow-up, 80.4% of participants were again classified as having cognitive impairment without dementia or had progressed to dementia. The annualized rate of progression to dementia was about 12%, whereas the rate of progression was 17% to 20% per year in the prodromal Alzheimer disease and stroke groups. Given the small sample sizes, differences in cognitive outcomes (chi-square, 14.84; P = 0.062) and mortality outcomes (chi-square, 4.19; P = 0.24) among the 4 most frequent subtypes did not reach standard significance levels. The 4 participants with amnestic mild cognitive impairment at baseline remained cognitively impaired without dementia at follow-up. Among those who had progressed to dementia at follow-up, 83% had Alzheimer disease, 16.7% had possible vascular dementia, and 0.4% had dementia of undetermined cause.
Outcomes of Cognitive Impairment without Dementia at Follow-up Assessment*