Estimating antemortem cognitive status of deceased subjects in a longitudinal study of dementia

Clinical decision trees for predicting conversion from cognitive impairment no dementia (CIND) to dementia in a longitudinal population-based study

The lack of gold standard diagnostic criteria for cognitive impairment in the absence of dementia has resulted in variable nomenclature, case definitions, outcomes, risk factors, and prognostic utilities. Our objective was to elucidate the clinical correlates of conversion to dementia in a longitudinal population-based sample. Using data from the Canadian Study of Health and Aging, a machine learning algorithm was used to identify symptoms that best differentiated converting from nonconverting cognitively impaired not demented participants. Poor retrieval was the sole predictor of conversion to dementia over 5 years. This finding suggests that patients with impaired retrieval are at greater risk for progression to dementia at follow-up. Employing significant predictors as markers for ongoing monitoring and assessment, rather than as clinical markers of conversion, is recommended given the less than optimal specificity of the predictive algorithms.

Patterns of cognitive decline, conversion rates, and predictive validity for 3 models of MCI

Our objective was to compare the predictive ability of different models of mild cognitive impairment (MCI) as a marker of incipient dementia in a longitudinal population-based Canadian sample. We examined the use of existing, well-documented MCI criteria using data from persons who underwent a clinical examination in the second wave of the Canadian Study of Health and Aging (CSHA). Demographic characteristics, average neuropsychological test performance, and sample frequencies and conversion rates were calculated for each classification. Receiver operating characteristic (ROC) analyses were employed to assess the predictive power of each cognitive classification. The highest sample frequencies and conversion rates were associated with case definitions of multiple-domain MCI. The only diagnostic criteria to significantly predict dementia 5 years later was the cognitive impairment no dementia (CIND)-2 case definition. More restrictive MCI case definitions fail to address the varying temporal increases in decline across different cognitive domains in the progression from normal cognitive functioning and dementia.

Effective normative samples for the detection of cognitive impairment in older adults

The inclusion of individuals with incipient dementia in normative data contaminates the distinction between normal and pathological aging. Conventional and Robust (excluding persons with incipient dementia) norms were created using data from the Canadian Study of Health and Aging (CSHA). Robust norms were not significantly better at distinguishing between normal and pathological aging. Norms reflecting the relationship between age and the prevalence of dementia revealed a probability of dementia of less than 35%. The results of the norming procedure serve to illustrate the validity of our current measures and methods for identifying cognitive impairment. CSHA Conventional norms are adequate for the identification of cognitive impairment.

Neuropsychological prediction of attrition due to death

In aging research, attrition bias produces underestimates of cognitive decline and limits the interpretation of cognitive change. Using data from the Canadian Study of Health and Aging, we identified neuropsychological predictors of death among not cognitively impaired (NCI) and cognitively impaired, not-demented (CIND) persons. For those with NCI, two neuropsychological measures significantly predicted attrition, over and above age, in the short term, while age was the best long-term predictor. The absence of neuropsychological predictors for the CIND group may reflect the group's etiological heterogeneity. In future research, the use of a more homogeneous subset of CIND may yield additional predictors.

Mapping the connections between education and dementia

Explanations for the association between educational attainment and the risk of dementia fall into three main categories. It may arise as an artefact of study methods; education may predict broader socioeconomic circumstances and exposures, or education may reflect brain reserve or cognitive capacity that protect against dementia. Data from the Canadian Study of Health and Aging (N=6646, giving 44,676 person-years of follow-up) are analyzed to test a series of hypotheses reflecting these explanations. Years of education showed a strong association with the risk of dementia (relative risk [RR] 2.1 for those with less than 6 years of education compared to those with 13 or more years; RR=2.9 among survivors). Possible artefactual factors were detected, but were insufficient to invalidate the association. Adjustments for a range of other socioeconomic indicators, health problems and lifestyle factors reduced, but did not remove, the association. Adjustments for intelligence and for an indicator of lifetime mental activity also appeared to account for some but not all of the association. The conclusion is that there appears to be a real association between educational attainment and the risk of dementia 50 to 60 years later; this influence appears to run through a number of different, and sometimes complementary, pathways.

Disease progression in vascular cognitive impairment: Cognitive, functional and behavioural outcomes in the Consortium to Investigate Vascular Impairment of Cognition (CIVIC) cohort study

BACKGROUND AND PURPOSE

Empirical studies to clarify the outcomes in Vascular Cognitive Impairment (VCI) are needed. We compared cognitive, functional, and behavioural outcomes in patients with VCI to patients with no cognitive impairment (NCI), and Alzheimer's disease (AD).

METHODS

Secondary analysis of the Consortium to Investigate Vascular Impairment of Cognition (CIVIC), a multi-centre Canadian memory clinic 30-month cohort study.

RESULTS

Of 1347 patients, 938 were eligible for follow-up, of whom 239 (24.5%) were lost and 29 (3%) had died. Of the remaining 697 patients, 125 had NCI, 229 had VCI, and 343 had AD at baseline. Compared to people with NCI, of whom 20-40% showed progression based on cognitive and functional measures, those with VCI were more likely to progress (50-65%), as were people with AD (50-80%) (p<0.01). More people with VCI showed progression of affective symptoms (30%) than those with NCI (12%) or AD (15% p<0.01). Progression of impaired judgment (rated clinically) in VCI (15%) was similar to AD (11%) but more common than in NCI (4%, p<0.01).

CONCLUSIONS

Most people with VCI show readily detectable progression by 30 months. Depressive symptoms were more common and more progressive in VCI than in Alzheimer's disease, whereas clinical evidence of progressive executive dysfunction was common in both AD and VCI.

Estimating the Incidence of Dementia: The Impact of Adjusting for Subject Attrition Using Health Care Utilization Data

PURPOSE

To estimate incidence rates for dementia and the impact of subject attrition on these rates.

METHODS

Crude, age- and gender-specific incidence rates of dementia and Alzheimer's disease were calculated using person-years analysis and Cox proportional hazard models in a population-based cohort study of 1952 adults aged 65+ years in Manitoba, Canada. Rates were standardized to the nondemented population using the direct method. Ratios of incidence rates comparing completers to subjects who had died, refused, or were unavailable for follow up were based on health care utilization data (available for all subject groups) and used to adjust rates for attrition.

RESULTS

Decedents had a significantly higher incidence of dementia than did subjects who completed the follow-up assessment. The incidence in subjects who refused or were unavailable at follow up was intermediate between decedents and completers. Adjusted for attrition, the standardized dementia incidence rate for community and institutional subjects was 25.3/1000 person-years, significantly higher than that based on follow-up assessments only (17.8/1000 person-years; 95% confidence interval: 14.3-21.4).

CONCLUSIONS

The impact of loss to follow up on incidence rates varies depending on the reason for subject attrition. Incidence studies of dementia should develop strategies to characterize and address subject attrition to avoid underestimating disease incidence.

Clinical and radiographic subtypes of vascular cognitive impairment in a clinic-based cohort study

BACKGROUND AND PURPOSE

There is a need for empirical studies to define criteria for vascular cognitive impairment (VCI) subtypes. In this paper, we report the predictive validity of a subtype classification scheme based on clinical and radiographic features.

METHODS

Nine Canadian memory clinics participated in the Consortium to Investigate Vascular Impairment of Cognition. This cohort consisted of 1347 patients, of whom 324 had VCI, and was followed for up to 30 months.

RESULTS

Clinical and neuroimaging features defined three subtypes: vascular cognitive impairment, no dementia, (n=97), vascular dementia (n=101) and mixed neurodegenerative/vascular dementia (n=126). Any ischemic lesion on neuroimaging increased the odds (odds ratio=9.31; 95% confidence interval 6.46, 13.39) of a VCI diagnosis. No VCI subtype, however, was associated with a specific neuroimaging abnormality. Compared to those with no cognitive impairment, patients with each VCI subtype had higher rates of death and institutionalization (hazard ratio for combined adverse events=6.08, p<0.001).

CONCLUSIONS

Both clinical features and radiographic features help establish a diagnosis of VCI. The outcomes of VCI subtypes, however, are more strongly associated with clinical features than with radiographic ones.

Index Variables for Studying Outcomes in Vascular Cognitive Impairment

Multivariable modeling in dementia risk factor studies is limited by the number of factors that can be analyzed practicably. Index variables, which integrate exposures, can efficiently reduce dimensionality. The Consortium to Investigate Vascular Impairment of Cognition study, a Canadian memory-clinic-based 30-month cohort study of 1,347 patients, used a vascular risk factor index (from 20 exposures) and a vascular clinical profile index (17 items). Patients with vascular cognitive impairment had higher index counts compared to those without cognitive impairment (0.16 +/- 0.11 vs. 0.07 +/- 0.07 for the risk factor index and 0.21 +/- 0.16 vs. 0.09 +/- 0.07 for the clinical profile index; p < 0.05). Both the death rate and the rate of cognitive impairment increased exponentially with the index variable (r > 0.90 for each index). The risk ratio for death was 1.12 (95% CI 1.09-1.15) for each increment of the risk factor index and was 1.23 (95% CI 1.1-1.28) for each increment of the clinical profile index. With each index, the areas under the receiver operating characteristic curves for predicting death and institutionalization ranged from 0.73 +/- 0.01 to 0.75 +/- 0.01. Construction of index variables that integrate multidimensional factors is a promising approach to assessing risk in multi-determined states.

Neuropsychological predictors of incident dementia in patients with vascular cognitive impairment, without dementia

BACKGROUND

Vascular cognitive impairment that does not fulfill dementia criteria (ie, vascular cognitive impairment, no dementia [CIND]) is common. Although progression to dementia is frequent, little is known about factors that predict progression. We examined whether performance on neuropsychological tests administered at baseline could predict incident cases of dementia in patients with vascular CIND after 5 years. Summary of Report- The Canadian Study of Health and Aging is a prospective, cohort study of 10 263 randomly selected persons aged > or =65 years. Of 149 people diagnosed with vascular CIND, 125 completed a battery of neuropsychological tests at baseline. Follow-up cognitive diagnoses were available for 102 individuals. After 5 years, 45 patients (44%) developed dementia. Low baseline scores on tests of memory and category fluency were associated with incident dementia.

CONCLUSIONS

Neuropsychological measures can indicate risk of dementia in patients with vascular CIND. This study did not suggest a prediction-to-progression profile distinct from that seen in Alzheimer disease.