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Objectives: To investigate the prevalence of changes in mood, personality, and behaviour in frontotemporal dementia (FTD) and Alzheimer's disease (AD) and hence, which features reliably distinguish between them. To establish whether the frontal and temporal variants of FTD are characterised by different behavioural changes.Methods: A questionnaire was designed to assess a wide range of neuropsychiatric changes; it incorporated features reported in previous studies of FTD and components of the neuropsychiatric inventory.(1) This was completed by 37 carers of patients with Alzheimer's disease (AD) and 33 patients with frontotemporal dementia (FTD), comprising 20 with temporal variant FTD (tv FTD) or semantic dementia and 13 with frontal variant FTD (fv FTD). An exploratory principal components factor analysis and discriminant function analysis was applied.Results: Factor analysis showed four robust and meaningful symptom clusters: factor 1-stereotypic and eating behaviour; factor 2-executive dysfunction and self care; factor 3-mood changes; factor 4-loss of social awareness. Only stereotypic and altered eating behaviour and loss of social awareness reliably differentiated AD from FTD with no effect of disease severity. By contrast, executive dysfunction, poor self care, and restlessness showed a significant effect of disease severity only, with the more impaired patients scoring more highly. Changes in mood were found to be equally prevalent in the three patient groups. Analysis of individual symptoms showed increased rates of mental rigidity and depression in the patients with semantic dementia compared with those with fv FTD. Conversely, the latter group showed greater disinhibition. Discriminant function analysis correctly classified 71.4% overall and 86.5% of the patients with AD.Conclusions: This questionnaire disclosed striking differences between patients with FTD and AD, but only stereotypic behaviour, changes in eating preference, disinhibition, and features of poor social awareness reliably separated the groups. The patients with fv FTD and semantic dementia were behaviourally very similar, reflecting the involvement of a common network, the ventral frontal lobe, temporal pole, and amygdala. Dysexecutive symptoms and poor self care were found to be affected by the severity of the disease, reflecting perhaps spread to dorsolateral prefrontal areas relatively late in the course of both FTD and AD. This questionnaire may be of value in the diagnosis and the monitoring of therapies. [ABSTRACT FROM AUTHOR]