Missing data? Plan on it!

Longitudinal study designs are indispensable for investigating age-related functional change. There now are well-established methods for addressing missing data in longitudinal studies. Modern missing data methods not only minimize most problems associated with missing data (e.g., loss of power and biased parameter estimates), but also have valuable new applications such as research designs that use modern missing data methods to plan missing data purposefully. This article describes two state-of-the-art statistical methodologies for addressing missing data in longitudinal research: growth curve analysis and statistical measurement models. How the purposeful planning of missing data in research designs can reduce subject burden, improve data quality and statistical power, and manage costs is then described.

Randomized, placebo-controlled, clinical trial of donepezil in vascular dementia: differential effects by hippocampal size

BACKGROUND AND PURPOSE

We sought to assess the efficacy and safety of donepezil in patients with vascular dementia (VaD) fulfilling National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l'Enseignement en Neurosciences criteria.

METHODS

This international, multicenter, 24-week trial was conducted from March 2003 to August 2005. Patients (N=974; mean age, 73.0 years) with probable or possible VaD were randomized 2:1 to receive donepezil 5 mg/d or placebo. Coprimary outcome measures were scores on the Vascular-Alzheimer Disease Assessment Scale-Cognitive Subscale and Clinician's Interview-Based Impression of Change, plus carer interview. Analyses were performed for the intent-to-treat population with the last-observation-carried-forward method.

RESULTS

Compared with placebo, donepezil-treated patients showed significant improvement from baseline to end point on the Vascular-Alzheimer Disease Assessment Scale-Cognitive Subscale (least-squares mean difference, -1.156; 95% CI, -1.98 to -0.33; P<0.01) but not on the Clinician's Interview-Based Impression of Change, plus carer interview. Patients with hippocampal atrophy who were treated with donepezil demonstrated stable cognition versus a decline in the placebo-treated group; in those without atrophy, cognition improved with donepezil versus relative stability with placebo. Results on secondary efficacy measures were inconsistent. The incidence of adverse events was similar across groups. Eleven deaths occurred in the donepezil group (1.7%), similar to rates previously reported for donepezil trials in VaD, whereas no deaths occurred in the placebo group.

CONCLUSIONS

Patients treated with donepezil 5 mg/d demonstrated significant improvement in cognitive, but not global, function. Donepezil was relatively well tolerated; adverse events were consistent with current labeling. Mortality in the placebo group was unexpectedly low. The differential treatment response of VaD patients by hippocampal size suggests that hippocampal imaging warrants further investigation for understanding VaD.

Sertraline improves executive function in patients with vascular cognitive impairment

The authors reviewed 35 open-label sertraline trials for executive impairment in ischemic cerebrovascular disease. Outcomes included clock-drawing, the Executive Interview (EXIT25), the Geriatric Depression Scale, and the Mini-Mental State Examination. Clinically "meaningful" improvement was defined as a >3.0 EXIT25 point decline from baseline. "Remission" was defined as the achievement of an EXIT25 score <15/50. Only EXIT25 scores improved significantly. Twenty patients (57.1%) experienced a clinically meaningful improvement in executive control function. Twelve (34.3%) achieved remission. Our findings suggest that sertraline may have both statistical and clinically meaningful effects on executive control function in ischemic cerebrovascular disease. The authors discuss the implications for future clinical trials.

Asymmetric insular function predicts positional blood pressure in nondemented elderly

Forty percent of nondemented octogenarians have Braak stages consistent with insular involvement, and may be at risk for "age-related" autonomic dysfunction. The authors examined the association between insular resting cerebral blood flow (rCBF) and cardiovascular functions in 29 nondemented elderly subjects who were highly screened to exclude comorbid cardiovascular disease. Mean insular rCBF was significantly higher on the right than left. However, 35.4% of participants had left dominant rCBF (a high-risk group). Right insular rCBF was significantly lower in the high-risk group. This subset had significantly increased positional drops in systolic blood pressure. While these data cannot address Alzheimer's disease as the specific cause, this possibility is being investigated in other cohorts.

Prospective evaluation of pretreatment executive cognitive impairment and depression in patients referred for radiotherapy

PURPOSE

Cancer patients are at risk of cognitive impairment and depression. We sought to ascertain the prevalence of executive, visuospatial, memory, and general cognitive performance deficits before radiotherapy in a radiation oncology clinic referral population and correlate the neurocognitive measures with the depression symptom burden.

METHODS AND MATERIALS

A total of 122 sequential patients referred for radiotherapy evaluation were administered a test battery composed of the Executive Interview (EXIT25), Executive Clock Drawing Task (CLOX1 and CLOX2), Mini Mental State Examination (MMSE), Memory Impairment Screen (MIS), and Geriatric Depression Scale (GDS). The mean age +/- standard deviation was 58 +/- 17 years. Of 122 patients, 24 (20%) had been referred for breast cancer, 21 (17%) for gastrointestinal cancer, 17 (14%) for genitourinary disease, and 8 (7%) for brain lesions; the rest were a variety of tumor sites. The cognitive performance among the tumor cohorts was compared using Bonferroni-corrected analysis of variance and Tukey-Kramer tests. Pearson correlation coefficients were determined between each cognitive instrument and the GDS.

RESULTS

Of the 122 patients, 52 (43%) exhibited a detectable executive cognition decrement on one or more test measures. Five percent had poor memory performance (MIS), 18% had poor visuospatial performance (CLOX2), and 13% had poor global cognition (MMSE). Patients with brain tumors performed substantially worse on the EXIT25. No between-group differences were found for CLOX1, CLOX2, MIS, or GDS performance. The EXIT25 scores correlated significantly with the GDS scores (r = 0.26, p = 0.005).

CONCLUSIONS

The results of this study have shown that patients referred for radiotherapy exhibit cognitive impairment profiles comparable to those observed in acutely ill medical inpatients. Executive control impairment appears more prevalent than global cognitive deficits, visuospatial impairment, or depression.

Depression, disability and intermediate pathways: a review of longitudinal studies in elders

Cross-sectional studies demonstrate depression is associated with disability in elders. These studies also report that disability in depressed elders is associated with greater medical illness burden, cognitive impairment, and behavioral changes. Only longitudinal studies, however, can determine the impact of depression and its comorbidities on functional decline. This review summarizes the findings of 20 longitudinal studies examining the relationship between baseline or incident depression and functional decline. However, the mediational effects of potential risk factors identified by cross-sectional studies cannot be derived from the current literature. We propose a mediational effects model for future longitudinal studies, incorporating measures sensitive to both mood symptoms and the medical, cognitive, and behavioral comorbidities of depression to better understand the impact of each on functional decline and to focus future clinical interventions.

Clock-drawing potentially mediates the effect of depression on mortality: replication in three cohorts

OBJECTIVE

Previously studies have associated visuospatial tasks, particularly 'clock-drawing', with mortality. We sought to determine whether clock-drawing also mediates the association between depressive symptoms and mortality.

PARTICIPANTS

Non-institutionalized Hispanic and non-Hispanic White elderly volunteers.

MEASUREMENTS

Survival curves were generated as a function of baseline depressive symptom ratings. Significant models were adjusted for CLOX performance. CLOX is divided into CLOX1, a measure of executive control, and CLOX2, a measure of visuospatial skills.

DESIGN

Retrospective analysis of three longitudinal cohorts.

RESULTS

CLOX2 and depressive symptoms were both associated with mortality in unadjusted models. CLOX2 predicted survival independently of CLOX1 in all three cohorts. CLOX2 also attenuated, and/or mediated the association between depressive symptoms and mortality. These results withstood adjustment for age and education in all three cohorts.

CONCLUSION

Regardless of the sample examined, or the measure of depressive symptoms applied, the association between depressive symptoms and mortality appears to be at least partially mediated by visuospatial skills. This finding supports our hypothesis that right hemisphere structural brain disease, particularly that involving the insula, may mediate depression's effects on mortality.

Insular Alzheimer disease pathology and the psychometric correlates of mortality

Right hemisphere dysfunction is associated with mortality in Alzheimer's disease (AD) and other neurologic conditions. These associations may be mediated by insular pathology, as insular lesions result in demonstrable changes in cardiovascular and autonomic control. AD affects the insulae at a preclinical stage, and insular AD pathology may be present in up to 40% of nondemented septuagenarians and octogenarians. This pathology can affect in vivo cardiac conduction and thereby dispose to cardiac arrhythmias and sudden death. Thus, AD pathology should be considered as a possible explanation for autonomic morbidity and mortality in nondemented elderly persons.

The cognitive correlates of functional status: a review from the Committee on Research of the American Neuropsychiatric Association

This report reviews the state of the literature and opportunities for research related to the cognitive correlates of functional status. The prediction of functional capacity on the basis of cognitive test performance is an important aspect of neuropsychological assessment. Moreover, functional impairment or "disability" is an essential part of dementia case finding. Nevertheless, relatively little attention has been given to the empirical study of the specific cognitive correlates of functional outcomes. What literature is available suggests that 1) the variance in functional status that can be specifically attributed to cognition is surprisingly modest; 2) some cognitive domains may be more relevant to functional capacity than others; 3) some measures of executive control function are relatively strong correlates of functional capacities, particularly medical or financial decision-making; and 4) "general" cognitive screening tests are surprisingly strong correlates of functional status. These findings are of particular significance to dementia case finding, epidemiology, and treatment. The extensive literature on functional status has yet to be integrated with the equally extensive literature on cognitive assessment. Better integration of cognitive and functional assessments would offer greater clinical utility. However, psychometric batteries may have to be redesigned to maximize their capacity to capture the variance in functional outcomes.

Clock drawing phenotypes in community-dwelling African Americans and Caucasians: results from the University of Alabama at Birmingham study of aging

BACKGROUND

Two dementia patterns have been described: 'type 1' dementia is characterized by executive function impairment and posterior cortical impairment, and 'type 2' dementia is characterized by executive impairment and relatively preserved posterior cortical function. The Executive Clock Drawing Task (CLOX) has been used to discriminate between type 1, type 2, and normal cognitive phenotypes. The aim of this study was to describe the prevalence of these phenotypes in community-dwelling African American and Caucasian elders.

METHODS

433 African Americans and 477 Caucasians over the age of 65 were recruited. Executive function was assessed using CLOX1, a command-directed clock drawing task. Posterior cortical impairment was assessed using CLOX2, a clock copy task. CLOX scores were combined to estimate the prevalence of type 1 phenotype (those with poor CLOX1 and CLOX2 performance) versus type 2 phenotype (those with only poor CLOX1 performance).

RESULTS

351 (39%) subjects had poor executive performance. Three hundred (33%) subjects had a type 1 phenotype and this pattern was 2.5 times more common among African Americans than Caucasians. One hundred and thirty-seven (15%) subjects had a type 2 phenotype with no significant difference between African Americans and Caucasians. African American ethnicity was independently associated with poor CLOX1 performance after adjusting for sociodemographic factors, posterior cortical function, and global cognition. CLOX2 performance was not associated with ethnicity.

CONCLUSION

The prevalence of poor executive performance in community-dwelling elders is high. African Americans were more likely to have a type 1 phenotype and these ethnic differences were not explained by sociodemographic variables alone.

Depression and Mortality in Elders Referred for Geriatric Psychiatry Consultation

OBJECTIVE

The association between depressive symptoms and mortality was assessed in a 7-year longitudinal follow-up of subjects referred for geropsychiatric consultation.

METHODS

The medical records of 89 referrals were reviewed. Survival analysis was performed on subjects stratified by Geriatric Depression Scale (GDS) and residential status.

RESULTS

Fifty percent of subjects with GDS > 6 (n = 28) died by 19 months versus 54 months for subjects with GDS < 7 (n = 61) (chi2 = 13.2, df = 1, P < .001). GDS, medical burden, age, and gender were independently associated with survival.

CONCLUSIONS

GDS scores greater than 6 are associated with increased risk of mortality in elders referred for geropsychiatric consultation.

Relationship between white matter fractional anisotropy and other indices of cerebral health in normal aging: Tract-based spatial statistics study of aging

White matter (WM) fractional anisotropy (FA) is thought to be related to WM integrity and decline in FA is often used as an index of decreasing WM health. However, the relationship of FA to other structural indices of cerebral health has not been well studied. We hypothesized that the decline in WM health will be associated with changes in several other indices of cerebral health. In this manuscript we studied the correlation between whole-brain/hemispheric/corpus callosum FA and gray matter (GM) thickness, sulcal span, and the volume of T2-hyperintense WM in a group of 31 healthy aging individuals (12 males/19 females) aged 57-82 years old. Individual subjects' FA measures were calculated from diffusion tracing imaging (DTI) data using tract-based spatial statistics--an approach specifically designed and validated for voxel-wise multi-subject FA analysis. Age-controlled correlation analysis showed that whole-brain average FA values were significantly and positively correlated with the subject's average GM thickness and negatively correlated with hyperintense WM volume. Intra-hemispheric correlations between FA and other measures of cerebral health had generally greater effect sizes than inter-hemispheric correction, with correlation between left FA and left GM thickness being the most significant (r=0.6, p<0.01). Regional analysis of FA values showed that late-myelinating fiber tracts of the genu of corpus callosum had higher association with other cerebral health indices. These data are consistent with the hypothesis that late-myelinating regions of the brain bear the brunt of age-related degenerative changes.

Cognitive predictors of mortality in elderly retirees: results from the Freedom House study

OBJECTIVE

The objective of this longitudinal cohort study was to study the cognitive domains associated with five-year longitudinal survival among healthy, well-educated, noninstitutionalized elderly.

METHODS

Survival curves were generated as a function of cross-sectional baseline cognitive test performance.

RESULTS

Nonverbal tests were significantly associated with survival. This finding was markedly consistent. Several nonverbal tasks were each significantly associated with survival independently of age, gender, baseline level of care, and healthcare utilization. In a multivariate model, copying a clock made the strongest, independent contribution to survival.

CONCLUSIONS

Right hemisphere integrity in general and nonverbal drawing tasks in particular have been associated with survival in conditions as diverse as Alzheimer disease, stroke, and epilepsy. This study extends this association to "normal" aging. The mechanism by which nonverbal cognitive function is related to mortality remains unclear but may be mediated by changes in right hemisphere cortical control of autonomic function. Nondemented older persons may be at risk. Clock drawing may provide a simple means of identifying them.

Executive function and capacity to consent to a noninvasive research protocol

OBJECTIVE

This study measured the association between executive function and decision-making capacity in subjects consenting to a noninvasive research protocol.

METHOD

Subjects consenting to a noninvasive research protocol (N = 21; mean age: 65.5 [standard deviation: 9.2] years) were administered a modified version of The MacArthur Competency Assessment Tool-Treatment (MacCAT-T), Executive Interview (EXIT25), Executive Clock Drawing Task (CLOX), and Mini-Mental State Examination (MMSE).

RESULTS

The EXIT25 was the only instrument to correlate with each decision-making capacity domain: understanding, appreciation, and reasoning.

CONCLUSIONS

Executive function as measured by the EXIT25 is associated with multiple decision-making capacity domains.

Mexican-American ethnicity and cognitive function: findings from an elderly southwestern sample

Relatively little is known about late-life patterns of cognitive function among Hispanics of Mexican heritage who reside in the United States. The authors designed a study to assess the association between Mexican-American ethnicity (defined in terms of childhood and adolescent developmental history) and cognitive function among elderly Mexican-American and non-Hispanic white residents of El Paso County, Texas. Our findings indicate significant associations between the degree of Mexican-American ethnicity and cognitive impairment on all three measures of cognitive function. These statistically significant findings remain after effects of education, age, and gender have been removed from the multiple regression equation. The authors conclude that a dependable and clinically meaningful negative association exists between Mexican-American ethnicity and late-life cognitive function in this region that is mediated by as yet unmeasured variables.

Insular Alzheimer's disease pathology as a cause of "age-related" autonomic dysfunction and mortality in the non-demented elderly

Only a few brain structures have been implicated in the autonomic control of blood pressure and heart rate. Among them are heteromodal association areas in the cortex, especially the insular cortex. Ischemic insular lesions have been associated with both cardiac arrhythmias and mortality. However, stroke may not be the only insular pathology with the potential to disrupt autonomic function. Alzheimer's disease (AD) is associated with both insular pathology and autonomic dysfunction. Alzheimer's dementia is merely the final stage of a pathological process that spans decades. Recent studies have demonstrated a hierarchichal sequence of AD pathology that includes the insular cortex. This may explain why AD has effects on BP and central autonomic cardio-regulatory functions. However, AD reaches the insular cortex at a "preclinical" stage in its development (i.e., before "dementia" can be diagnosed). Thus, AD pathology should also be considered as a possible explanation for autonomic morbidity and mortality in non-demented elderly persons. We hypothesize that autonomic dyscontrol, commonly seen in non-demented well elderly persons without significant cardiovascular disease (CVD), reflects subclinical stages of AD pathology affecting the insular cortex. If true, then preclinical AD pathology should be considered as a possible explanation for arrhythmia/fall related morbidity and mortality in non-demented elderly persons.

The impact of medical illness on executive function

Executive function can be defined as one's ability to plan, initiate, sequence, monitor, and inhibit complex goal-directed behaviors. Although executive impairment is generally associated with dementia, recent studies have suggested that patients with chronic diseases, such as hypertension, chronic obstructive pulmonary disease, and diabetes, may also have executive deficits independent of psychiatric comorbidities. Because executive function is associated with functional outcomes, medication compliance, and the capacity to give informed consent, it is important that it be assessed. However, it is the authors' impression that executive function is not adequately assessed in medical settings, despite the availability of reliable measures. This article reviews the impact of medical illness on executive function and discusses practical diagnostic instruments and treatment strategies. The changes in functional status associated with executive impairment as well as pathophysiology and treatment strategies are also discussed.