Diagnostic role of FDG PET in dementia

Learning Objectives 1. To emphasize FDG PET in early and differential diagnosis of dementia (D) as an important diagnostic tool. 2. To demonstrate commonly seen FDG PET patterns in dementia.

Summary: PET is a valuable tool for understanding the correlation between biological and structural changes in various D. Alzheimer's disease (AD) is the most common form of D. Differentiating between AD and other D, like frontotemporal D (FTD) including Pick’s disease, vascular D (VD), D with Lewy Bodies (LB) and Parkinson’s disease (PD) is important, since the natural history and management differ. The pattern of AD in FDG PET include hypometabolism of parietal, temporal, and posterior cingulate cortices early in the course of the disease, with relative sparing of primary sensorimotor and primary visual cortices and sparing of striatum, thalamus, and cerebellum. This biparietal pattern, while not pathognomic for AD, is highly predictive of AD and may be particularly pronounced in patients with age less than 65 years. In FTD, frontal cortex and anterior temporal and mesiotemporal areas are affected earlier or with greater initial severity than are parietal and lateral temporal cortices, with relative sparing of primary sensorimotor and visual cortices. In D with LB, deficits are similar to those of AD, but with less sparing of occipital cortex and possibly cerebellum. In VD, hypometabolism affects cortical, subcortical, and cerebellar areas. In PD D, deficits are similar to those of AD, but with more sparing of mesiotemporal area and less sparing of visual cortex. Here are some of the examples of commonly seen patterns of D on PET.