Lew body dementia and Posterior cortical variant Alzheimer's disease: Similarities and differences on FDG PET and TRODAT scan

To illustrate the similarities and differences in the imaging patterns of Posterior cortical atrophy (PCA), and Dementia with Lewy bodies (DLB) on FDG PET and correlation with TRODAT scan. A retrospective analysis of 30 patients of clinically suspected posterior dementia was done. All the subjects underwent F-18 FDG PET CT scan of the brain and the studies were analyzed both qualitatively (visually) and semi quantitatively. The subjects had undergone dopamine transporter imaging with Tc 99 m TRODAT 1 on a prior date. The subjects were divided into possible PCA with TRODAT scan normal (n = 10) and possible DLB with TRODAT scan abnormal (n = 20). The FDG uptake patterns were recorded and areas of cortical hypometabolism in the cerebral cortex that were two standard deviations from the mean were considered as abnormal. All the subjects had an abnormal pattern of F-18 FDG uptake on PET scan, both on visual inspection and semiquantitative analysis. Bilateral parieto-occipital hypometabolism was consistently found in all the subjects. Hypometabolism in precuneus, posterior cingulate and the cortex around the angular gyrus was present in all the subjects of PCA with relative sparing of the medial occipital cortices. DLB subjects showed variable degrees of involvement of the medial occipital cortices with relative sparing of posterior cingulate and precuneus regions. FDG PET scan may act as a non invasive diagnostic modality in differentiating the two posterior cortical dementias despite significant clinical and imaging overlap with or without additional TRODAT scan.