Relationship between behavioural and psychological symptoms of dementia and cognition in Alzheimer's disease.

BACKGROUND: Behavioural and psychological symptoms of dementia (BPSDs) are common. It is unclear whether associations are stronger with the absolute cognitive level or that relative to premorbid mental ability.

METHODS: The Neuropsychiatric Inventory (NPI) was administered to carers of patients with Alzheimer's disease (AD). Patients underwent cognitive testing with the National Adult Reading Test (NART) to estimate premorbid IQ and 6 tests of current cognitive function.

RESULTS: 556 patients, mean age 77.3 years, had NPI scores. The total NPI score correlated significantly with most cognitive test scores, but multi-linear regression identified NART-IQ as the only significant cognitive predictor (beta=-0.17, p=0.008). Principal component analysis of the 10 NPI domains extracted 3 components corresponding to mood, frontal and psychotic factors. The NPI mood factor correlated significantly with NART-IQ (rho=-0.14, p=0.014) and lexical verbal fluency (rho=-0.09, p=0.034) only. The NPI frontal factor correlation with NART-IQ approached significance (rho=-0.11, p=0.053). The NPI psychotic factor correlated significantly with the Mini-Mental State Examination (rho=-0.15, p<0.001) and the Hopkins verbal learning test (rho=-0.11, p=0.013) scores.

CONCLUSION: The relationship between BPSDs and cognition in AD is weak and largely explained by premorbid IQ. There is a stronger relationship between current cognition and psychotic symptoms.