P1-244: Frequency of hemispheric metabolic asymmetry in probable Alzheimer's disease

Abstract

Alzheimer's disease (AD) causes, on average, a symmetric pattern of glucose hypometabolism. However, some patients have hypometabolism predominantly affecting either the left or right hemisphere. These patients may have atypical presentations that could cause them to be systematically excluded from clinical drug trials. It is unknown whether the left or right hemisphere is more likely to be selectively affected. Furthermore, the frequency of significant hemispheric metabolic asymmetry is unknown. We evaluated 95 baseline FDG-PET scans in patients with clinically diagnosed mild AD (MMSE 20–27) enrolled in the Alzheimer's Disease Neuroimaging Initiative (ADNI). Each scan was analyzed with Neurostat, providing 3D-stereotactic surface projection (3D-SSP) maps of glucose metabolism relative to pons and corresponding statistical maps of Z-scores computed in comparison to 27 cognitively normal elderly control subjects. We visually evaluated the pattern of glucose hypometabolism, considering 5 regions in each hemisphere typically affected in dementia. Hemispheric asymmetry was considered significant when hypometabolism was 2 or more standard deviations greater in one hemisphere. We also calculated 3D-SSP maps of mean rates of glucose metabolism and Z-score maps. Ten patients had an FTD-like pattern of hypometabolism and were excluded from further analyses. In the remaining 85 AD subjects, FDG-PET images were symmetric in 70 (82.4%). Hypometabolism predominantly involved left hemisphere regions in 8 (9.4%) and predominantly involved right hemisphere regions in 7 (8.2%). These groups did not differ significantly in age or dementia severity as measured by MMSE. Impairment was greater in naming and word fluency for patients with predominant left hemisphere hypometabolism and clock drawing scores were lowest for those with predominant right hemisphere hypometabolism. Although AD patients as a group have completely symmetric glucose hypometabolism, individual patterns vary reflecting cognitive differences. In this sample, roughly similar proportions of left and right predominant hypometabolism was seen in a minority of patients. The frequency of metabolic asymmetry may differ in community samples. The mechanisms accounting for selective involvement of one hemisphere are unexplained and need to be explored further. Supported in part by the Center for Alzheimer's Care, Imaging and Research and NIH grant AG024904.