Amyloid PET Positivity in Different Primary Progressive Aphasia Phenotypes

Purpose Primary progressive aphasia (PPA) is a neurological syndrome in which language functions become progressively impaired with relative sparing of memory and other instrumental functions. The pathologic causes of PPA are heterogeneous, but studies suggest that logopenic PPA (LPA) is underpinned by Alzheimer disease (AD) pathology in a high proportion of cases. The purposes of this descriptive and retrospective study were to characterize 18F-florbetapir PET imaging in a group of patients with a clinical syndrome of PPA, to determine the value of clinical characterization based on language phenotype in predicting the underlying pathology of PPA with 18F-florbetapir, and to quantify amyloid load in PPA subjects classified as "positive" 18F-florbetapir scans. Then, we compare the quantification and distribution of 18F-florbetapir uptake with those of typical, predominantly amnestic AD patients. Methods We conducted a PET study with 18F-florbetapir in a cohort of 12 right-handed patients diagnosed with PPA: 3 patients with semantic-variant PPA, 5 with nonfluent PPA, 1 with LPA, and 3 unclassifiable patients. We evaluated amyloid deposition between APP groups and 11 patients with typical amnestic AD. Results Among the 12 patients with PPA syndrome, 8 (66.7%) were considered as amyloid positive. One of the 3 patients with semantic-variant PPA was 18F-florbetapir positive. In contrast, 4 of the 5 nonfluent-variant PPA, 2 of the 3 unclassifiable cases and the single patient with LPA were 18F-florbetapir positive. A significantly higher 18F-florbetapir uptake was observed in PPA 18F-florbetapir–positive patients compared with typical AD patients. This difference was observed in all regions of interest, except in posterior cingulate and temporal cortex. Conclusions These results suggest that 18F-florbetapir PET may be useful in a routine clinical procedure to improve the reliability of identifying AD pathology in patients with PPA syndrome, with different clinical subtypes of the PPA syndrome.

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