Cognition and behaviour are independent and heterogeneous dimensions in Alzheimer's disease

Clinical expressions of cognition and behaviour in Alzheimer's disease (AD) patients are heterogeneous. Therefore, assessing the entire range of selective cognitive and behavioural characteristics of dementia in minute detail is extremely important. However, considering that groups of different symptoms may respond to the same pharmacological agent, it is also evident that a correct evaluation of the behaviour requires the grouping of symptoms in fewer syndromes. Thus, the authors have analysed various connections between selective cognitive domains and behavioural symptoms (BPSD) in probable AD outpatients. Two hundred and forty four patients with diagnosis of probable AD, according to DSM-IV and NINCDS-ADRDA criteria were enrolled. The evaluation included the Mini Mental State Examination, the Mental Deterioration Battery, and the Neuropsychiatric Inventory. Treatment with low doses of neuroleptic drugs only was allowed. Principal component analysis condensed the 18 cognitive/behavioural variables in 7 factors namely general-cognitive, constructional abilities, hyperactivity, psychosis, anxiety, mood-excitement and mood-depression/apathy. None of the cognitive domains were included in the behavioural factors and vice-versa. Furthermore, the only BPSD which impaired continuously with progression of disease severity was apathy which was also the most severe symptom. In conclusion, many cognitive and behavioural syndromes exist in patients with AD. However, the results of this study suggest that cognition and behaviour are independent dimensions.