Introduction The frontotemporal dementia (FTD) consortium criteria (2011) emphasise the importance of distinguishing possible and probable behavioural variant FTD (bvFTD). A significant number of possible patients with bvFTD do not show functional decline and remain with normal neuroimaging over time, thus exhibiting the bvFTD phenocopy syndrome. A neurodegenerative nature is unlikely but an alternative explanation is missing. Our aim was to detect psychiatric conditions underlying the bvFTD phenocopy syndrome after extensive evaluation.

Methods We included patients with the bvFTD phenocopy syndrome whereby patients with probable bvFTD served as a control group. Patients had to have undergone both neurological and psychiatric evaluation. Their charts were reviewed retrospectively. Using both qualitative and quantitative methods, psychiatric and psychological conditions associated with the clinical syndrome were determined in both groups and their relative frequencies were compared.

Results Of 181 suspected bvFTD cases, 33 patients with bvFTD phenocopy syndrome and 19 with probable bvFTD were included. Recent life events, relationship problems and cluster C personality traits were the most prevalent psychiatric/psychological conditions. The frequency of these conditions was higher in the group of patients with the bvFTD phenocopy syndrome (n=28) compared to the probable bvFTD group (n=9) (χ² p<0.05).

Conclusions This is the first study thoroughly exploring psychiatric causes of the bvFTD phenocopy syndrome, revealing that in most cases multiple factors played a contributory role. Our study gives arguments for neurological and psychiatric collaboration when diagnosing bvFTD. Prompt diagnosis of treatable psychiatric conditions is to be gained.