Theory of mind in behavioural-variant frontotemporal dementia and Alzheimer's disease: a meta-analysis.

Current evidence suggests that neurocognitive testing has limited practical benefit in distinguishing behavioural-variant frontotemporal dementia (bvFTD) and Alzheimer's disease (AD). In this meta-analysis of 30 studies, theory of mind (ToM) performances of 784 individuals with bvFTD (n=273) and AD (n=511) were compared with 671 healthy controls. ToM performances of 227 patients with bvFTD and 229 with AD were also compared in studies matched for general cognition. ToM was impaired in both bvFTD (d=1.79) and AD (d=1.15). In bvFTD, patients were particularly impaired in advanced tasks such as recognition of faux pas and sarcasm (d>2.0). In AD, ToM deficits were relatively modest. In studies matched for general cognition, ToM was significantly impaired in bvFTD in comparision to AD (d=1.29), especially for faux pas recognition (d=1.75). ToM dysfunction is a robust and more specific feature of bvFTD. In contrast, ToM deficits are modest compared with level of general cognitive impairment in AD. In both disorders, longer duration of disease and level of general cognitive impairment are related to relatively more severe ToM deficits. Assessment of ToM can be beneficial for early identification of bvFTD.