Comprehensive qualitative characterization of linguistic performance profiles in primary progressive aphasia: a multivariate study with FDG-PET

Primary progressive aphasia (PPA) classification relies on profile characterization of quantitatively impaired/spared performance in language tasks. In this study, we coextracted 8 qualitative types of errors in 67 PPA patients submitted to a comprehensive language assessment. Canonical correlation analysis was applied to simultaneously correlate qualitative errors and brain metabolism, collected with FDG-PET. Results showed the contribution of semantic, syntactic and working memory errors associated with specific correlates of regional metabolic changes. Reduced metabolism in the left fusiform gyrus, anterior-middle and inferior-temporal gyri and middle-temporal pole correlated with an increase of semantic errors. Hypometabolism in the left inferior, middle, and superior frontal gyri, insula and right middle-occipital gyrus was related to syntactic errors. Higher metabolism in the bilateral pallidum, putamen, and left thalamus, as well as hypometabolism in the left angular and supramarginal gyri, inferior-parietal lobule, posterior-middle and inferior-temporal gyri and posterior cingulum predicted the increase of working memory errors. A relevant role of working memory subcomponents was associated with distinct neural systems. Patients' profiles are easily represented in a qualitative multidimensional space, in which mixed PPA overlapped with different phenotypes.