P2-255: Do atrophy rates accelerate in MCI and normal aging?

Abstract

The brain atrophies among the healthy elderly but atrophies at a faster rate among those with mild cognitive impairment (MCI). It is unclear whether atrophy rates are relatively constant or accelerate in these groups. This can be assessed by measuring brain volume at 3 or more points in time. To evaluate whether rates of brain atrophy accelerate in 3 groups of subjects: cognitively normal elderly; patients with MCI who convert to probable Alzheimer's disease (AD); and MCI patients who remain stable. 42 cognitively normal elderly controls were age and gender matched to 42 MCI subjects who converted to AD. 28 MCI subjects who did not convert to AD were individually matched to 28 patients from the larger MCI converter cohort. All subjects had 3 or more serial MRI scans. The scan acquired at conversion from MCI to AD was used as the index point in MCI converters. Matched age defined the index point in controls and stable MCIs. Rates of whole brain (WB) and ventricle volume change were measured before and after the index scan using the boundary shift integral technique. Rate acceleration was defined by the difference between the rates before and after the index scan. In MCI converters, median rate acceleration occurred in WB (from 8.4 cc/yr before conversion to 11.2 cc/yr after conversion, p=0.036) and in ventricle (3.4 cc/yr before conversion to 4.3 cc/yr after conversion, P=0.007). Ventricular expansion rates also accelerated in controls (p=0.008) and stable MCIs (p=0.013), while WB atrophy rates did not. The rates of acceleration (i.e. the difference in atrophy rate before vs. after index date) observed in MCI converters were not statistically significantly different from those seen in normals (P=0.17 for WB, P=0.25 for ventricle) or in MCI stables (P=0.10 for WB, P=0.64 for ventricle), although the trend towards a difference was suggestive for WB. Measures of ventricular expansion accelerate in all 3 subject groups and are highly sensitive to progressive shrinkage of the brain over time. Conversely the rate of WB atrophy may have greater specificity in mapping onto the changing clinical course in MCI converters.