FDG-PET in the diagnosis of primary progressive aphasia: a systematic review

Abstract

Primary progressive aphasia (PPA) is a disease known to affect the frontal and temporal regions of the left hemisphere. PPA is often an indication of future development of dementia, specifically semantic dementia (SD) for frontotemporal dementia (FTD) and logopenic progressive aphasia (LPA) as an atypical presentation of Alzheimer's disease (AD). The purpose of this review is to clarify the value of 2-deoxy-2-[18F]fluoro-D-glucose (FDG)-positron emission tomography (PET) in the detection and diagnosis of PPA. A comprehensive review of literature was conducted using Web of Science, PubMed, and Google Scholar. The three PPA subtypes show distinct regions of hypometabolism in FDG-PET imaging with SD in the anterior temporal lobes, LPA in the left temporo-parietal junction, and nonfluent/agrammatic Variant PPA (nfvPPA) in the left inferior frontal gyrus and insula. Despite the distinct patterns, overlapping hypometabolic areas can complicate differential diagnosis, especially in patients with SD who are frequently diagnosed with AD. Integration with other diagnostic tools could refine the diagnostic process and lead to improved patient outcomes. Future research should focus on validating these findings in larger populations and exploring the therapeutic implications of early, accurate PPA diagnosis with more targeted therapeutic interventions.

Keywords: 2-deoxy-2-[18F]fluoro-D-glucose; FDG; Neurology; PET; Positron emission tomography; Primary progressive aphasia.

Fig. 1

Representation of the regions of hypometabolism with the three primary progressive aphasia (PPA) variants. Reproduced with permission from Bekkhus-Wetterberg, Peter et al. [25]

Fig. 2

PRISMA flowchart: This diagram visually represents the flow of information throughout the different phases of the systematic review. It provides an overview of the number of identified records, including those that were included and excluded

Fig. 3

Delineation of hypometabolic regions at [¹⁸F] fluorodeoxyglucose positron emission tomography (FDG-PET) which can aid in differentiation subtypes of primary progressive aphasia. The blue areas indicate the nonfluent/agrammatic subtype, green indicates the semantic subtype, and yellow represents the logopenic subtype. Reproduced with permission from Matías-Guiu et al. [19]

Fig. 4

18F-FDG PET scan patterns for focal-onset dementias using Neurostat 3D-SSP where Lat lateral, LBD Lewy body dementia, Lt left, Med medial, Rt right. Reproduced with permission from Taswell et al. [20]