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

Frontotemporal dementia (FTD) occurs in two main clinical subtypes, which can transition into one another: the behavioral variant (bvFTD) and the language variant (primary progressive aphasia; PPA). It is common for the latter, as primary progressive aphasia (PPA), to transition into bvFTD; however, the opposite development, where bvFTD is followed by "secondary progressive aphasia," has received little attention. This constellation is particularly challenging to recognize as frontal dysexecutive syndrome can confound subsequent progressive aphasia as impulsive behavior, a lack of inhibition, and apathy can lead to non-aphasic communication disturbances, including impoverished syntax, reduced cognitive flexibility, and insufficient error monitoring. A 78-year-old patient, with a disease duration of 10 years, was initially diagnosed in the 3rd year of the disease with corticobasal syndrome (CBS) with frontal behavioral-spatial syndrome (CBS-FBS) and subsequently with CBS with progressive non-fluent aphasia (CBS-PNFA) in the 4th year. Severe ophthalmoplegia was the reason for changing the diagnosis in the seventh year to progressive supranuclear palsy with CBS predominance type (PSP-CBS). The pathological diagnosis was FTLD-tau in the form of a PSP subtype. The MRI showed asymmetric atrophy, particularly of the left insular cortex and the left inferior frontal gyrus. The 2-[