Neurocognitive disorder due to Alzheimer's disease (AD) in old age is accompanied by various Behavior and Psychological Symptom of Dementia (BPSD). And its relevance with delusions, one of BPSD in particular is attracting attention of researchers as AD patients with delusions have shown more BPSD and the quality of life in caregivers were deteriorated. Therefore, it is important to investigate the delusions for better understanding of neurocognitive disorder due to AD and improvement of the quality of caregivers.
In study 1, the present study confirmed the previous findings of AD characteristics. AD patients reported the most apathy and the least elation among various BPSD symptoms. In addition, the higher the disease severity, the more BPSD was accompanied. Also the cognitive and daily life function of the BPSD group were reported to have lower scores compared to the non-BPSD group.
The purpose of the Study 2 was to investigated the characteristics of AD patients with delusions compared to those without delusions. First of all, AD patients reported more BPSD and slower psychomotor speed and more daily living dysfunctions when they have delusions at the present evaluation. In the longitudinal approach, immediate recall ability was significantly reduced in verbal memory test between delusion and non-delusion groups based on the first evaluation of delusion. And the verbal fluency in COWAT_animal test as well as daily living dysfunction were significantly decreased as the AD has deteriorated and delusion occurred. Also delusion group that already demonstrated poor cognitive function compared to the non-delusion group based on the first evaluation of delusion also has shown poorer cognitive function compared to the non-delusion group.
In Study 3, the characteristics of cognitive and daily living functions were examined according to the subtypes of delusions. Misidentification subtypes of delusion demonstrated poorer cognitive and daily living function than persecution subtypes of delusions. The theft delusion, one of the persecution subtypes in delusions, was related to memory impairment and non-theft delusion was related to frontal/execution function.
To sum up, the present study confirmed that delusions of AD in old age were highly related to the cognitive and daily living dysfunction. This suggests that preventive and rapid therapeutic interventions in delusions could help patients maintain good cognitive and daily living functions by themselves and/or their caregivers, which might in turn reduce the probability of developing delusion in AD.