Dissociating Social Inappropriateness in the Frontal and Temporal anatomic subtypes of the Behavioral variant of Frontotemporal Dementia

Abstract

Social inappropriateness is a prominent feature of the ‘frontal’ and ‘temporal’ subtypes of the behavioral variant of frontotemporal dementia (bvFTD); however, the relative contribution of both regions remains unclear. The aim of this study was to examine whether appropriate and inappropriate social behaviors as reported on the Social Norms Questionnaire (SNQ) could discriminate frontal and temporal subtypes of bvFTD. Using data from the National Alzheimer’s Coordinating Center (NACC), three dementia subgroups were compared. Groups were matched in dementia severity, age, and education and included (a) 23 bvFTD patients with circumscribed frontal atrophy (F-bvFTD), (b) 11 bvFTD patients with circumscribed temporal lobe atrophy (T-bvFTD), and (c) 11 semantic variant of primary progressive aphasia patients (svPPA) with circumscribed left temporal lobe atrophy. Performance by dementia groups was compared to 25 older controls with normal cognition (NC) matched in age and education. The SNQ is comprised of two subscale scores: break norms and overadhere errors. The SNQ was administered in the context of a larger standardized neuropsychological battery at NACC affiliated centers. After controlling for the effects of language using a one-way ANCOVA, the T-bvFTD group endorsed significantly more inappropriate social behaviors (i.e., higher break norms errors score) than all groups with medium effect size (F (3, 65) = 15.25, p < .0001, PES = .41). Interestingly, the F-bvFTD group performed similarly to the NC group. No other significant differences were found on the SNQ total and subscale scores. Hierarchical multiple linear regression analysis showed that approximately 20% of the variance in SNQ break norms subscale score performance was explained by performance on neuropsychological semantic tests. Additional variance explained by executive function and empathy measures was less than 4%. Social inappropriateness may partially arise from a deficit in knowledge of normative behavior in the ‘temporal’ behavioral variant of FTD. Clinical implications are discussed.