Metabolic imaging patterns in posterior cortical atrophy and Lewy body dementia

Abstract

Purpose To study the imaging patterns of Posterior cortical atrophy (PCA) and Dementia with Lewy bodies (DLB) on fluoro-deoxyglucose positron emission tomography computed tomography ([18F]FDG PET/CT), identify areas of overlap and differences and to develop a prediction model to assist in diagnosis using univariate and multivariate analysis. Methods A retrospective analysis of 72 patients clinically suspected of having posterior dementia was done. All patients underwent [18FF]FDG PET/CT of the brain and dopamine transporter imaging with [[99mTc]TRODAT-1 SPECT scan on separate days. The patients were divided into PCA with normal TRODAT uptake (n=34) and DLB with abnormal TRODAT uptake (n=38). The FDG PET/CT uptake patterns were recorded and areas of significant hypometabolism by z score analysis were considered as abnormal. Receiver operator characteristics (ROC) curve analysis was used to determine cutoff z scores and binary logistic regression analysis was used to determine the Odds ratio of being in the predicted groups. Results Significantly hypometabolism was found in parieto-temporo-occipital association cortices and cingulate cortices in PCA patients. DLB patients showed significantly reduced uptake in the visual cortex. No significant difference was found between z score of occipital association cortex which showed hypometabolism in both groups. The cut-off z-score values derived from the ROC curve analysis were as follows- parietal association (cut-off-3, sensitivity-65.6%, specificity - 68.7%), temporal association (cut-off-2, sensitivity-78%, specificity-75%) and posterior cingulate (cut-off-0.5, sensitivity-93.7%, specificity-40.6%), their respective Odds ratio (with 95% confidence interval) for being in the PCA group as derived from univariate logistic regression were 3.66 (1.30–10.32), 10.71 (3.36–34.13) and 7.85 (1.57–39.17). The cut-off z score of primary visual cortex as derived from ROC curve was zero with sensitivity of 87.5%, specificity of 71.9%, and the Odds ratio for being the in the DLB group was 24.7 with 95% confidence interval of 5.99–101.85. Conclusion [18F]FDG PET may be useful as a non-invasive diagnostic modality in differentiating the two posterior cortical dementias, despite significant overlap. Primary visual cortical hypometabolism can serve as an independent diagnostic marker for DLB, even in the absence of TRODAT imaging.

Seeing the Woods for the Trees? Applying Diagnostic Criteria for Dementia with Lewy Bodies to Patients Presenting with Posterior Cortical Atrophy

“…Fluorodeoxyglucose positron emission tomography (FDG-PET) can demonstrate patterns of hypometabolism sensitive in differentiating AD from DLB, namely a temporoparietal distribution of hypometabolism in the former versus a more occipital distribution in the latter 9. However, such methods of differentiation have not been validated in PCA-AD which demonstrates overlap in metabolic imaging findings with DLB due to the more posterior location of hypometabolism 10. While quantitative imaging analysis techniques may prove useful in overcoming such pitfalls,10 further research is required to clarify the utility of imaging in differentiating PCA-AD from PCA-Plus which, given the unifying clinical findings, may demonstrate similar patterns of cortical atrophy and therefore be less sensitive.…”

“…9 However, such methods of differentiation have not been validated in PCA-AD which demonstrates overlap in metabolic imaging findings with DLB due to the more posterior location of hypometabolism. 10 While quantitative imaging analysis techniques may prove useful in overcoming such pitfalls, 10 further research is required to clarify the utility of imaging in differentiating PCA-AD from PCA-Plus which, given the unifying clinical findings, may demonstrate similar patterns of cortical atrophy and therefore be less sensitive. CSF biomarkers have become an increasingly valuable element of the PCA work-up and should always be considered if available.…”

Imaging Clinical Subtypes and Associated Brain Networks in Alzheimer’s Disease

“…DLB is associated with metabolic impairment in primary visual cortex which usually is spared in PCA, while the posterior cingulate gyrus is relatively preserved in PCA (“cingulate island sign”) [ 86 ]. However, some studies found a considerable overlap of patterns [ 87 ] or better discriminatory power for PCA with metabolic reduction in lateral temporal than in posterior cingulate cortex [ 88 ].…”

Neuroimaging in Dementia With Lewy Bodies

“…Molecular imaging modalities, such as single-photon emission tomography (SPECT) and fluorine-18fluorodeoxyglucose positron emission imaging (FDG-PET), have played a pivotal role in understanding the complex pathophysiology of DLB by assessing metabolic activity in vivo with the correct radiotracers involved [14]. In DLB, metabolic studies show hypometabolism involving the occipital cortex, visual association areas, and posterior parietotemporal region [15]. However, in a comparative study, no significant differences were observed between PDD and DLB in terms of FDG uptake while PD patients without dementia exhibited similar profiles of metabolism as healthy controls [16].…”