Environmental dependency behaviours in frontotemporal dementia: have we been underrating them?

Environmental dependency (ED) behaviours, such as imitation behaviour (IB) and incidental utilization behaviour (UB), are considered pathognomonic of a frontal lesion and can play a unique role in diagnosing behavioural variant frontotemporal dementia (bvFTD). However, with only few focused observations of ED behaviour reported in earlier studies, their roles in the diagnosis of bvFTD have so far remained supportive. In this observational study, conducted in the cognitive clinic of a tertiary-care hospital, we explored the hypotheses that a focused and systematic search could uncover more ED behaviours in patients with bvFTD, and that the presence of ED behaviours such as incidental UB and IB should allow us to cleanly differentiate bvFTD from AD. Forty-one bvFTD patients and 75 probable AD patients, all diagnosed using accepted criteria, were seen by a neurologist and a neuropsychologist. Information regarding ED behaviour was obtained from the caregiver's history, observations for spontaneous behaviour and induction of the behaviour in the clinic. All ED behaviours were significantly more frequent in bvFTD compared with AD. UB (78 %; 66 % incidental) and IB (59 %) occurred exclusively in bvFTD. Multi-pronged and focused clinical assessment contributed to the high frequency of ED behaviours. Nearly two-thirds of bvFTD patients, but none with AD, showed three or more ED behaviours. We concluded that ED behaviours are more common in bvFTD than is currently recognized. UB, IB or three ED behaviours, if present, could clearly differentiate bvFTD from AD. A focused search should consistently uncover ED behaviours in bvFTD patients.