Longitudinal volumetric MRI change and rate of cognitive decline

Abstract

Objective: To examine how baseline and change of volumetric MRI relate to cognitive decline in older individuals.

Background: Memory is associated with hippocampal integrity, whereas executive function has been linked to impaired frontal lobe function. Previous studies have shown that hippocampal and cortical atrophy are more strongly related to cognition than are measures of subcortical cerebrovascular disease (CVD). The authors hypothesized that memory (MEM) decline would be related to change in hippocampal volume (HC), whereas decline in executive function (EXEC) would be related to change of cortical gray matter volume (CGM) and measures of subcortical CVD.

Methods: Subjects from a multicenter study (n = 103) included cognitively normal, mildly impaired, and demented cases with and without subcortical lacunes. All had longitudinal cognitive evaluation (mean = 4.8 years) and two or more MRI scans at least one year apart (mean = 3.4 years). MRI measures included HC, CGM, total lacune volume (LAC), and white matter hyperintensity volume (WMH). Random effects modeling of longitudinal data assessed effects of MRI baseline and MRI change on baseline and change of psychometrically matched measures of MEM and EXEC.

Results: Change in MEM was related to HC baseline and HC change. Change in EXEC was related to baseline CGM and to change in CGM, HC, and LAC. Results were unchanged when demented cases were excluded. WMH was not associated with change in MEM or EXEC independent of HC, CGM, and LAC.

Conclusion: Hippocampal volume was the primary determinant of memory decline, whereas executive function (EXEC) decline was related to multiple brain components. Results support a hypothesis that MEM decline is strongly influenced by Alzheimer disease (AD), whereas EXEC decline may be complexly determined by cerebrovascular disease and AD.

Figure

Longitudinal trajectories of memory and executive function representing model-predicted average scores at yearly time points for four hypothetical cases. The NORM case was defined by normal MRI at all time points. The Alzheimer disease (AD) case had a normal baseline MRI, but cortical gray matter volume and hippocampal volume decline at a rate commensurate with typical AD. The subcortical ischemic vascular disease (SIVD) case was defined by incident lacunes in years 2 and 4. The SIVD + AD case was defined by a combination of typical AD and incident lacunes in years 2 and 4. Details about how these cases were defined are presented in the text.