Networks Disrupted in Linguistic Variants of Frontotemporal Dementia

Abstract

The non-fluent/agrammatic variant of primary progressive aphasia (nfvPPA) and semantic variant (svPPA) of frontotemporal dementia (FTD) are neurodegenerative diseases. Previous works have shown alterations of fractional anisotropy (FA) and mean diffusivity (MD) from diffusion tensor images (DTIs). This manuscript is aimed at using DTI images to build a global tractography and to identify atrophy patterns of white matter in each variant. Twenty patients with svPPA, 20 patients with nfvPPA, 26 patients with behavioral variant of FTD (bvFTD) and, 33 controls were included. An analysis based on the connectivity of structural networks showed changes in FA and MD in svPPA and nfvPPA with respect to bvFTD. Much damage in the internal networks of the left temporal lobe was found in svPPA patients; in contrast, patients with nfvPPA showed atrophy in networks from the basal ganglia to motor and premotor areas. Those findings support the dual stream model of speech and language.

Language in Behavioral Variant Frontotemporal Dementia: Another Stone to Be Turned in Latin America

“…In particular, emerging evidence ( 67 ) suggests that, compared with healthy controls, LA bvFTD patients produce fewer and smaller semantic clusters (words retrieved according to semantic subcategories such as pets, birds, or felines, for animals) as well as fewer switches (shifts from one semantic subcategory to another). Semantic fluency deficits in LA bvFTD patients seem less strong than those observed in non-fluent and semantic variant PPA [( 70 , 74 , 75 ), but see ( 69 )] but as severe as those of patients with amnestic mild cognitive impairment ( 67 ) and AD ( 64 , 67 , 68 , 72 , 73 ).…”

“…Semantic fluency assessments also reveal systematic deficits in LA bvFTD samples ( 58 , 67 – 70 , 72 , 74 , 75 ). As is the case with phonemic fluency, this impairment is consistent for both Spanish ( 74 , 75 ) and Portuguese ( 67 , 68 , 72 ), in cohorts with different mean ages (varying from 61.9 to 70.2 years old) and education levels (year of education ranging from 8.7 to 16.0 years).…”

“…Semantic fluency assessments also reveal systematic deficits in LA bvFTD samples ( 58 , 67 – 70 , 72 , 74 , 75 ). As is the case with phonemic fluency, this impairment is consistent for both Spanish ( 74 , 75 ) and Portuguese ( 67 , 68 , 72 ), in cohorts with different mean ages (varying from 61.9 to 70.2 years old) and education levels (year of education ranging from 8.7 to 16.0 years). In particular, emerging evidence ( 67 ) suggests that, compared with healthy controls, LA bvFTD patients produce fewer and smaller semantic clusters (words retrieved according to semantic subcategories such as pets, birds, or felines, for animals) as well as fewer switches (shifts from one semantic subcategory to another).…”

“…LA bvFTD patients have impaired phonemic fluency relative to healthy controls ( 56 – 58 , 60 , 68 – 70 , 72 , 74 , 75 ). This has been observed for both Spanish-speaking ( 57 , 60 , 74 , 75 ) and Portuguese-speaking ( 68 , 72 ) cohorts, across different age groups (mean age varying from 64.4 to 70.2 years old) and education levels (years of education ranging from 10.8 to 16.0 years). Non-significant differences were reported by Torralva et al ( 62 ), although these results came from a smaller sample with higher MMSE scores than those reported in other studies.…”

“…Also, phonemic fluency outcomes do not differ significantly between bvFTD and AD [( 58 , 68 , 72 , 73 ), but see ( 60 )]. Comparisons with PPA have yielded mixed results: while some studies report better performance for bvFTD than non-fluent variant PPA and semantic variant PPA patients ( 74 , 75 ), other found no significant difference between groups ( 60 , 69 , 70 ). 1 Phonemic fluency performance in LA bvFTD patients has been shown to correlate with the volume of core affected regions –e.g., the bilateral insula and putamen, the right amygdala, fusiform and inferior frontal gyri, and the left superior temporal and orbitofrontal cortices ( 57 ).…”