Focal thalamus pathology in frontotemporal dementia: Phenotype-associated thalamic profiles

Background: The clinical phenotypes of frontotemporal dementia (FTD) are defined by distinctive clinical features and associated with unique cortical atrophy patterns. Clinical manifestations in FTD however are not solely driven by cortical pathology, but stem from the selective dysfunction of corticobasal circuits, the majority of which are relayed through thalamic nuclei. The objective of this study is the systematic radiological characterisation of thalamic pathology across the clinical spectrum of FTD to describe phenotype-associated thalamic signatures.Methods: 170 participants were included in a multimodal, prospective neuroimaging study to evaluate thalamic degeneration at a nuclear, vertex, and morphometric level using a uniform imaging protocol and a multimodal analysis approach.Results: Patients with behavioural variant FTD (bvFTD), non-fluent variant primary progressive aphasia (nfvPPA), semantic variant primary progressive aphasia (svPPA) and amyotrophic lateral sclerosis-FTD (ALSFTD) exhibit distinctive thalamic disease-burden profiles with the preferential degeneration of specific thalamic nuclei. While vertex analyses reveal largely overlapping thalamic atrophy patterns, morphometric analyses successfully capture focal intra-thalamic degeneration.Conclusions: Mirroring selective cortical vulnerability, focal rather than global thalamic atrophy characterises the clinical subtypes of FTD. Thalamic degeneration is a likely contributor to the heterogeneity of clinical manifestations observed in FTD. As thalamic imaging techniques capture different facets of pathological change and differ in their sensitivity to detect distinguishing features, future studies should implement a multimodal approach with complementary MRI techniques.