Defining repetitive behaviours in frontotemporal dementia.

Repetitive behaviors are common manifestations of Frontotemporal dementia. Patients with FTD present with various types of repetitive behaviors with unique behavioral and cognitive substrates, including compulsivity, lack of impulse control, stereotypy, and hoarding. Other sources of repetitive behaviors, such as restrictive interests and insistence on sameness, may also be seen in FTD. Although repetitive behaviors are highly prevalent and potentially discriminatory in this population, their expression varies widely between patients and the field lacks consensus about the classification of these behaviors. Terms used to describe repetitive behaviors in FTD are highly heterogeneous and may lack precise definitions. This lack of harmonization of definitions for distinct forms of repetitive behavior limits the ability to differentiate between pathological behaviors and impedes understanding of their underlying mechanisms. This review examines established definitions of well-characterized repetitive behaviors in other neuropsychiatric disorders and proposes operational definitions applicable to patients with FTD. Building on extant models of repetitive behaviors in non-human and lesion work, and models of social behavioral changes in FTD, we describe the potential neurocognitive bases for the emergence of different types of repetitive behaviors in FTD and their potential perpetuation by a predisposition towards habit formation. Finally, examples of distinct therapeutic approaches for different forms of repetitive behaviors are highlighted, along with future directions to accurately classify, measure, and treat these symptoms when they impair quality of life.