Executive function and instrumental activities of daily living in mild cognitive impairment and Alzheimer's disease

Abstract

Background: Impairment in instrumental activities of daily living (IADL) leads to early loss in productivity and adds significant burden to caregivers. Executive dysfunction is thought to be an important contributor to functional impairment. The objective of this study was to investigate the relationship between executive function and IADL in a large cohort of well-characterized normal older controls, mild cognitive impairment (MCI), and patients with mild Alzheimer's disease, separately as well as across the entire sample, while accounting for demographic, cognitive, and behavioral factors.

Methods: Subjects with baseline clinical datasets (n=793) from the Alzheimer's Disease Neuroimaging Initiative study (228 normal older controls, 387 MCI, 178 Alzheimer's disease) were included in the analysis. A multiple regression model was used to assess the relationship between executive function and IADL.

Results: A multiple regression model, including diagnosis, global cognitive impairment, memory performance, and other covariates demonstrated a significant relationship between executive dysfunction and IADL impairment across all subjects (R2=.60, P<.0001 for model; Digit Symbol, partial ß=-.044, P=.005; Trailmaking Test B-A, quadratic relation, P=.01). Similarly, an analysis using MCI subjects only yielded a significant relationship (R2=.16, P<.0001 for model; Digit Symbol, partial ß=-.08, P=.001).

Conclusions: These results suggest that executive dysfunction is a key contributor to impairment in IADL. This relationship was evident even after accounting for degree of memory deficit across the continuum of cognitive impairment and dementia.

Figure 1

Predicted values of FAQ vs. diagnostic group and DSym from the multiple regression model, which also included TMT-B-A, age, MMSE, curvilinear terms for RAVLT delayed recall and NPI-Q Apathy item, and an interaction of MMSE with diagnostic group. In this graph, other variables (age, MMSE, RAVLT, NPI-Q Apathy, TMT-B-A) are held constant at their grand mean values. The local density of the actual values is indicated by the density of symbols. Error bars indicate the root mean square above and below the predicted value (not shown for NC because of floor effect). Note the negative relation of DSym to FAQ within diagnostic groups, additive to the level effects of the diagnostic groups themselves. AD (Alzheimer’s disease), DSym (Digit Symbol), FAQ (Functional Activities Questionnaire), MCI (mild cognitive impairment), MMSE (Mini-Mental State Examination), NC (normal control), NPI-Q Apathy (Neuropsychiatric Inventory Questionnaire brief form, apathy item), RAVLT (Rey Auditory Verbal Learning Test), TMT-B-A (Trailmaking Test B minus Trailmaking Test A).

Figure 2

Predicted values of FAQ vs. diagnostic group and TMT-B-A from the multiple regression model, which also included DSym, age, MMSE, curvilinear terms for RAVLT delayed recall and NPI-Q Apathy item, and an interaction of MMSE with diagnostic group. In this graph, other variables (age, MMSE, RAVLT, NPI-Q Apathy, DSym) are held constant at their grand mean values. The local density of the actual values is indicated by the density of symbols. Error bars indicate the root mean square above and below the predicted value (not shown for NC because of floor effect). Note the relation of TMT-B-A to FAQ within diagnostic groups, additive to the level effects of the diagnostic groups themselves. AD (Alzheimer’s disease), DSym (Digit Symbol), FAQ (Functional Activities Questionnaire), MCI (mild cognitive impairment), MMSE (Mini-Mental State Examination), NC (normal control), NPI-Q Apathy (Neuropsychiatric Inventory Questionnaire brief form, apathy item), RAVLT (Rey Auditory Verbal Learning Test), TMT-B-A (Trailmaking Test B minus Trailmaking Test A).