Case Report: Behavioral variant FTD confounding a language variant FTD in a case of PSP-CBS

Alexandra Veronika Jürs ^1,2 Elisabeth Kasper ¹ Manuela Neumann ^3,4 Jens Kurth ⁵ Bernd Joachim Krause ⁵ Daniel Cantré ⁶ Johannes Prudlo ^1,7*

• ¹ Department of Neurology, University Medical Center Rostock, Rostock, Germany
• ² Translational Neurodegeneration Section „Albrecht Kossel“, Department of Neurology, University Medical Center Rostock, Rostock, Germany
• ³ Department of Neuropathology, University of Tübingen, Tübingen, Germany
• ⁴ German Center for Neurodegenerative Diseases (DZNE), Tübingen, Germany
• ⁵ Department of Nuclear Medicine, Medical Center Rostock, Rostock, Germany
• ⁶ Institute of Diagnostic and Interventional Radiology, Pediatric Radiology and Neuroradiology, University Medical Center Rostock, Rostock, Germany
• ⁷ German Center for Neurodegenerative Diseases (DZNE), Rostock, Germany

Frontotemporal dementias (FTD) occur in two main clinical subtypes, which can transition into one another: the behavioral variant (bvFTD) and the language variant. It is common that the latter as a primary progressive aphasia (PPA) transitions to a bvFTD; however, the opposite development, that a bvFTD is followed by a "secondary progressive aphasia" has received little attention. This constellation is particularly challenging to recognize as the frontal dysexecutive syndrome can confound a subsequent progressive aphasia as impulsive behavior, a lack of inhibition, and apathy can lead to nonaphasic communication disturbances including impoverished syntax, reduced cognitive flexibility, and insufficient error monitoring.A 78-year-old patient with a disease duration of ten years was initially diagnosed in the 3 rd year of the disease with corticobasal syndrome with a fronto-behavioral-(spatial) phenotype (CBS-FBS) and subsequently with a CBS with progressive non-fluent aphasia (CBS-PNFA) in the 4 th year. A severe ophthalmoplegia was the reason for changing the diagnosis in the 7 th year to progressive supranuclear palsy with a CBS predominance type (PSP-CBS). The pathological diagnosis was FTLD-tau in the form of a PSP-subtype. The MRI showed an asymmetric atrophy particularly of the left insular cortex and the left inferior frontal gyrus. The 2-[ 18 F]FDG-PET revealed a left-accentuated bifrontal glucose hypometabolism.This case report draws attention to how progressive neurodegenerative aphasias can occur in FTD not only as a primary language phenomenon (in the sense of PPA) but also as a secondary phenomenon (following a primary behavioral disorder with non-aphasic communication disorder). The dysexecutive syndrome can mask the aphasia. Therefore, incorporating spontaneous speech tasks into standard neuropsychological language tests in addition to MRI and PET imaging techniques could better recognize such secondary aphasias even in the presence of a dysexecutive syndrome and thus broaden our understanding of the natural history of FTDs.