IC-P-078: Brain SPECT patterns associated with different profiles of memory impairment in amnestic MCI

Abstract

In view of upcoming treatment options for AD in the predementia stage, it is crucial to identify features that predict conversion to AD within a population of amnestic MCI (aMCI). It has been suggested that MCI of AD type may present with a memory profile indicating medial temporal lobe dysfunction. We recently demonstrated that patients with aMCI and mild AD are impaired on a visual recognition memory task (DMS48). This finding may be related to early neuropathological change in rhinal cortices, thought to be crucial for visual recognition memory. The aim of this study was to characterize the pattern of brain SPECT perfusion of patients with mild aMCI according to their performance on the DMS48. 26 patients with mild aMCI were divided in two subgroups according to their Z–score on the DMS48. 13 patients obtained a Z–score ≤ –1.5 (“DMS48+ group”) and 13 below (“DMS48– group”). Mean age and MMSE score did not differ between the two groups (69yrs ±7; MMSE score: 27.4±1). Brain perfusion was studied using 99mTc–ECD SPECT. A voxel–by–voxel group analysis was performed with SPM2 (p<0.01c). In the DMS48+ group, hypoperfusion of the left prefrontal cortex was found, including orbitoventral and dorsolateral areas (Figure A). In contrast, in the DMS48– group, bilateral hypoperfusion of medial temporal lobe structures and temporobasal cortices extending to the temporo–occipital junction on both sides was observed. In this group, there was also bilateral hypoperfusion of the temporo–parietal associative cortex and right posterior cingulum (Figure B). Two groups of patients with mild aMCI, classified according to their performance on a visual recognition memory task, were found to exhibit distinctive patterns of cerebral hypoperfusion. The DMS48+ group showed left prefrontal hypoperfusion and no abnormality in medial temporal lobe structures. This suggests that their memory impairment may be related to prefrontal dysfunction that interferes with encoding/retrieval processes, in particular for verbal material. The DMS48– group showed hypoperfusion in medial temporal lobes, in posterior associative cortex and in the cingulum, a pattern usually described in early AD. Combined SPECT and evaluation of visual recognition memory may be useful to identify aMCI patients of the AD type.