Background: The proportion of the population aged 85 years and older has increased rapidly in Japan, reaching 2.5 million (1.99%) in 2002. Under these circumstances, the number of dementia patients increases annually. However, few studies have focused on Alzheimer's disease (AD) with an age at onset older than 85 years (oldest old AD). The aims of the present study were to determine the prevalence of the behavioral and psychological symptoms of dementia (BPSD) in patients with oldest old AD compared with those with young old AD. Methods: Fifty-eight untreated AD patients were divided into two groups: young old AD patients (age at onset between 65 and 70 years; n = 28) and oldest old AD patients (age at onset 85 years or older; n = 30). Then, BPSD were compared between the two groups. Results: There were significant differences in the frequencies of hallucinations (κ 2 = 7.43; P = 0.011) and delusional misidentification syndrome (DMS; κ 2 =7.26; P = 0.011) between the two groups. Conclusions: The results of the present study suggest that aging may play a part in the occurrence of hallucinations and DMS in oldest old AD patients.
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