Differential diagnosis of neurodegenerative dementias using metabolic phenotypes on F-18 FDG PET/CT

Abstract

Positron emission tomography (PET) imaging with F-18 fluorodeoxyglucose (FDG) can be used as a downstream marker of neuronal injury, a hallmark of neurodegenerative dementias. Characteristic patterns of regional glucose metabolism have been used to classify the dementia subtypes, namely Alzheimer's dementia (AD), frontotemporal dementia (FTD), diffuse Lewy body (DLBD) and vascular dementia (VD). We undertook this study to assess the utility of FDG-PET in the differential diagnosis of dementia subtypes. One hundred and twenty-five patients diagnosed with dementia were referred from cognitive disorders and memory clinics of speciality neurology centres for the FDG-PET study. Imaging-based diagnosis of dementia type was established in 101 patients by visual assessment of individual scans by a PET physician blinded to the clinical diagnosis. The results were compared with an 18-month follow-up clinical assessment made by the specialist neurologist. Concordance of visual evaluation of FDG-PET scans with clinical diagnosis of the dementia type was achieved in 90% of patients scanned. This concordance was 93.4% for AD, 88.8% for FTD, 66.6% for DLBD and 92.3% for the other dementia syndromes. FDG-PET performed after the initial work-up of dementias is useful for supporting the clinical diagnosis of dementia subtype.

Keywords: AD; DLBD; FDG-PET; FTD; vascular dementia.

Figure 1

A) Transaxial fused FDG-PET/CT images in a case of advanced AD showing symmetrical hypometabolism in both frontal and temporal cortices (arrow). B) Coronal fused FDG-PET/CT image showing hypometabolism in both parietal cortices (arrow). C) Sagittal fused FDG-PET/CT image showing hypometabolism in the precuneus (arrow). D) Lateral maximum intensity projection image showing hypometabolism in the parietal and frontal cortices with preserved metabolism in the sensorimotor, visual and occipital cortices, and both cerebellar hemispheres.

Figure 2

Transaxial fused FDG-PET/CT images in a case of fronto-temporal dementia showing hypometabolism in both frontal (A, arrow) and both anterior temporal cortices (B, arrow).

Figure 3

Transaxial fused FDG-PET/CT images in a case of DLBD showing hypometabolism in both frontal and parietal cortices (A) and also in the visual cortices (B, arrow). C) Lateral maximum intensity projection image showing hypometabolism in the visual cortices with preserved metabolism in the posterior cingulate (arrow).