Abstract
The mechanism underlying delusion in Alzheimer's disease patients has not been fully clarified; however, the occurrence of delusion is a critical issue for dementia patients and their caregivers. In Japan, delusion of theft is the most frequent delusion in AD patients. We examined the risk factors for delusion of theft in AD patients showing mild dementia. Fifty-six AD patients were administered HDS-R, MMSE and COGNISTAT, including the ‘speech sample’, to assess their neuropsychological and social cognitive functions. The age, years of education, presence of cohabiting family members and premorbid personality traits were obtained from family members. About 25.0% of AD patients showed delusion of theft (D-group), and 75% did not (non-D-group). About 33.3% of female patients and 5.9% of male patients were included in the D-group (p < 0.05). About 13.6% of patients who were cohabiting with family members and 66.7% of patients who were living alone were included in the D-group (p < 0.05). About 35.1% of patients who had a neurotic personality and 5.3% of patients who did not were included in the D-group (p < 0.05). There were no significant differences in scores on HDS-R, MMSE and COGNISTAT sub-scales, except for ‘speech sample’, between the two groups. In the ‘speech sample’, 38.7% of patients who understood a relationship between two boys and 12.0% of patients who did not were included in the D-group (p < 0.05). These results indicated that delusion of theft in AD patients was related to female gender, absence of cohabiting family members, neurotic personality and retained social cognitive function.
Introduction
In Japan, there are 26 million elderly people who are 65 years of age or older, accounting for 20% of the approximately 130 million population in 2005. One out of the 13 elderly people of age 65 years or older, and one out of the four elderly people of age 85 years of or older have dementia. The presence of dementia patients is an important social issue not only in Japan, but also throughout the world.
Especially, the occurrence of behavioural and psychological symptoms in dementia (BPSD) is a critical issue for dementia patients and their caregivers because it frequently leads to a reduction in quality of life (Deimling & Bass, Citation1986), early institutionalization (Colerick & George, Citation1986), and progression of cognitive dysfunction (Haupt, Romero, & Kurz, Citation1996; Jeste, Wragg, Salmon, Harris, & Thal, Citation1992; Ropacki & Jeste, Citation2005). Delusion is the most frequent BPSD in Alzheimer's disease (AD) patients, and its prevalence has been reported to be about 36%, ranging from 9.3 to 63% (Ropacki & Jeste, Citation2005). The mechanism underlying delusion in AD patients, however, has not been fully clarified (Lee et al., Citation2007; Mizrahi, Starkstein, Jorge, & Robinson, Citation2006). Some studies reported that delusion in AD patients was related to female gender (Bassiony & Lyketsos, Citation2003; Ikeda et al., Citation2003; Ozawa, Citation1997; Rao & Lyketsos, Citation1998), whereas other studies reported that males were more likely to have delusions than females (Burns, Jacoby, & Levy, Citation1990), or there was no significant difference in terms of gender (Migliorelli et al., Citation1995). The relations between delusion and age (Migliorelli et al., Citation1995; Ozawa, Citation1997), educational level (Jeste et al., Citation1992) and severity of dementia (Swearer, Drachman, O’Donnell, & Mitchell, Citation1988; Teri, Larson, & Reifler, Citation1988) have also been controversial in previous studies (Ballard & Oyebode, Citation1995; Bassiony & Lyketsos, Citation2003; Cummings & Victoroff, Citation1990; Kazui et al., Citation2006; Ropacki & Jeste, Citation2005).
As for cognitive function, some studies reported that there was a significant correlation between delusion and scores on generalized cognitive psychological tests such as the Mini Mental State Examination (MMSE) (Folstein, Folstein, & McHugh, Citation1975; Haupt et al., Citation1996; Jeste et al., Citation1992; Takechi, Yamada, Sugihara, & Kita, Citation2006), whereas other studies reported that there was no significant correlation (Burns et al., Citation1990; Ikeda et al., Citation2003; Migliorelli et al., Citation1995). Only a few studies have examined the relation between delusion and particular neuropsychological cognitive functions. Jeste et al. (Citation1992) reported that there were significant differences between AD patients with and without delusion in scores on the MMSE, blessed information memory concentration test and dementia rating scale, and that there were no significant differences in scores on the Boston naming test, number information test, verbal fluency test, block design subtest in WISC-R, clock drawing test, modified Wisconsin card sorting test and similarities sub-scales in WAIS-R. In Migliorelli's study (Migliorelli et al., Citation1995), there were no significant differences between AD patients with and without delusion in scores on various psychological tests, including the Boston naming test, Raven's progressive matrices test and several tests for executive function, in addition to the MMSE. It is, however, a critical point that severity of dementia among patients was not controlled in these studies, so it is not clear which delusion or severity of dementia is related to these findings. A previous study using patients with similar MMSE scores reported that there were no significant differences between delusion and cognitive functions in psychological tests estimating some verbal functions, non-verbal functions or executive functions (Burns et al., Citation1990). In addition, cognitive functions include not only neuropsychological cognitive functions such as memory, orientation, construction, language and executive functions, but also social cognitive functions. It is also important to examine the relation between delusion and social cognitive functions because delusion is frequently caused by interpersonal relations.
One reason why the mechanism underlying delusion in AD patients has not been clarified may be the fact that previous studies have examined delusion without distinguishing between different delusions such as delusion of theft, delusion of infidelity or jealousy, somatic delusions and delusions of grandeur. These delusions represent different notions; for example, in delusion of theft the patient believes ‘People are stealing my things’, in somatic delusions the patient feels ‘There are subcutaneous worms in my arm’, and in delusions of grandeur the patient believes ‘I am the greatest man’. These delusions may also have different mechanisms, so it is necessary to study the mechanism of each delusion in dementia patients separately.
In Japan, delusion of theft is the most frequent delusion in AD patients (Ikeda et al., Citation2003; Ozawa, Citation1997), although there have been few studies concerning this delusion. Ikeda (Citation2004) reported that there were no significant differences in sub-scale scores on the Alzheimer's disease Assessment Scale (ADAS) between AD patients with and without delusion of theft. Takechi et al. (Citation2006) reported that there were no significant differences in scores on the word fluency test, category cued memory test and clock drawing test between AD patients with and without delusion of theft, although there was a significant difference in their MMSE scores. Other studies also reported that there was no significant correlation between delusion of theft and cognitive functions (Kazui et al., Citation2006; Terada et al., Citation2005).
Another reason why the mechanism underlying delusion in AD patients has not been clarified may be the fact that previous studies have underestimated the importance of psychosocial factors other than cognitive functions. The presence of cohabiting family members or premorbid personality traits may be general psychosocial risk factors for delusion, especially delusion of theft.
In the present study, we examined the risk factors for delusion of theft in AD patients showing mild dementia, focusing on social cognitive functions, cohabiting family members and premorbid personality traits, which have so far been rarely examined, in addition to gender, age, years of education and neuropsychological cognitive functions.
Methods
Alzheimer's disease patients were recruited from a special dementia outpatient department at a general hospital in Tokyo, from May 2004 to April 2006. Fifty-six AD patients met the NINCDS-ADRDA criteria for the clinical diagnosis of probable AD (McKhann et al., Citation1984), had no previous history of psychiatric disorders, and had a score of one in the Clinical Dementia Rating (CDR) (Hughes, Berg, Danziger, Coben, & Martin, Citation1982), corresponding to mild dementia. These patients and/or their families gave informed consent.
Delusion of theft was defined as a ‘People are stealing things’ delusion based on the Behavioural Pathology in Alzheimer's Disease Rating Scale (BEHAVE-AD) (Reisberg et al., Citation1987). About 14 of the 56 AD patients (25.0%) showed delusion of theft (D-group), and the remaining 42 patients (75.0%) did not (non-D-group).
All 56 AD patients were administered the revised version of Hasegawa's dementia scale (HDS-R) (Kato et al., Citation1991), MMSE and the Japanese version of the Neurobehavioural Cognitive Status Examination (COGNISTAT) (Matsuda & Nakatani, Citation2004). The HDS-R and MMSE are the most popular screening measures for evaluation of neuropsychological cognitive functions in Japan and worldwide, respectively. The COGNISTAT consists of 11 sub-scales: ‘orientation’, ‘attention’, ‘speech sample’, ‘comprehension’, ‘repetition’, ‘naming’, ‘constructional ability’, ‘memory’, ‘calculation’, ‘similarities’ and ‘judgement’. Scores on these sub-scales are calculated based on a Z score, except for the ‘speech sample’. The ‘speech sample’ requires patients to tell the story of a cartoon. The cartoon is usually explained as ‘A fishing boy has fallen asleep. He does not realize that a fish is pulling his fishing line. Another boy riding a bicycle on a bridge is trying to wake him up.’ In the present study, the responses to this task were classified into 1 or 0 based on whether the patients understood the relationship between the two boys or not. This task was used as an indicator of social cognitive functions. Other tasks that have been used to evaluate social cognitive functions (Gregory et al., Citation2002; Maylor, Moulson, Muncer, & Taylor, Citation2002) were difficult to apply to AD patients showing mild dementia.
The age, years of education and presence of cohabiting family members were obtained from the patients and/or their family members. In addition, the family members were questioned about any premorbid personality traits of the patients and were required to answer with ‘yes’ or ‘no’ about responses of the patients to past events.
In statistical analyses, the quantitative data (age, years of education and scores on the MMSE, HDS-R and COGNISTAT excluding the ‘speech sample’) were analysed by the t-test, and the qualitative data (gender, presence of cohabiting family members, premorbid personality traits and ‘speech sample’) were analysed by Fisher's exact probability test and logistic regression analysis. In all tests, the null hypothesis was rejected at a significance level of p < 0.05.
Results
The data on the mean age, years of education and MMSE and HDS-R scores in the AD patients are shown in . There were no significant differences in these factors between the D-group and non-D-group by t-tests. No significant differences in MMSE and HDS-R scores between the two groups indicated that the severity of dementia was controlled as well as the same score on the CDR was found in the AD patients.
Table 1. Age, years of education, MMSE and HDS-R scores of the AD patients.
The data on gender, presence of cohabiting family members, premorbid personality traits and ‘speech sample’ are shown in . For gender, the female AD patients more frequently showed delusion of theft than the male AD patients (p < 0.05).
Table 2. Qualitative data on the AD patients.
As for the presence of cohabiting family members, more AD patients were living alone in the D-group than in the non-D-group (p < 0.05). More AD patients were not cohabiting with their spouses or both their spouses and children in the D-group than in the non-D-group (p < 0.05), although there was no significant difference in cohabitation with their children. As for the cohabiting children, all AD patients lived with the son or daughter, and two of the four in the D-group and eight of the 11 in the non-D-group lived with the son and his wife or the daughter and her husband, although there were no significant differences.
As for premorbid personality traits, the AD patients who had a neurotic personality before AD developed more frequently showed delusion of theft than the AD patients who did not (p < 0.05). On the other hand, there was no significant difference between the AD patients who had an extrovert personality before AD developed and the AD patients who did not.
On COGNISTAT, both the D-group and non-D-group achieved low scores on ‘orientation’, ‘constructional ability’ and ‘memory’. There were no significant differences on all sub-scales except for the ‘speech sample’ between the two groups (). For ‘speech sample’, the AD patients who understood the relationship between the two boys in the cartoon more frequently showed delusion of theft than the AD patients who did not (p < 0.05) (). The AD patients who did not understand the relationship between the two boys explained the cartoon as ‘this is a boy, a fish and a bridge.’
Table 3. Sub-item scores on COGNISTAT.
Logistic regression analysis was used to identify significant predictors for delusion of theft (the independent variables were gender, presence of cohabiting spouse and/or children, neurotic and extrovert personalities, and ‘speech sample’). As a result, this analysis was significant (p < 0.01), but only a neurotic personality tended to be related to delusion of theft (Odds ratio (OR) = 9.922, 95%-confidence interval (CI) = 0.720–136.826, p < 0.10), while the other variables showed no significant relations.
Discussion
The risk factors for delusion in AD patients have not been fully clarified, although delusion is the most frequent symptom. In the present study, delusion was restricted to delusion of theft, because the variety of delusions may be one reason that risk factors for delusion have been uncertain in previous studies. Also, delusion of theft is the most frequent delusion in AD patients in Japan. Further, severity of dementia was controlled to mild dementia (CDR = 1) in all our AD patients, because the risk factors for delusion may be different according to the severity of dementia. The age and years of education between the D-group and non-D-group were also controlled.
In the present study, 25% of the AD patients showed delusion of theft, essentially in agreement with the previous results (Ozawa, Citation1997; Ropacki & Jeste, Citation2005). The female AD patients showed significantly more frequent delusion of theft than the male AD patients. This result confirms the results of previous studies, especially Japanese studies (Bassiony & Lyketsos, Citation2003; Ikeda et al., Citation2003; Ozawa, Citation1997; Rao & Lyketsos, Citation1998). The higher prevalence of delusion of theft in the female AD patients may be related to the fact that housework has been traditionally done by a wife in Japan, so housewives have more opportunities to deal with the household items like purses, clothes and tableware, and housewives with AD cannot find lost household items and can easily develop delusion of theft. Further studies are needed to clarify this relationship.
In the presence of cohabiting family members, the AD patients who were living alone showed significantly more frequent delusion of theft than the AD patients who were cohabiting with their families. The AD patients who were not cohabiting with their spouses or both their spouses and children showed significantly more frequent delusion of theft than the AD patients who were. In contrast, there was no significant correlation between cohabitation with children and prevalence of delusion of theft. The lower prevalence of delusion of theft in the AD patients who were cohabiting with their families may be explained by their families' support to find lost things and/or their families' management of important things such as bankbooks. The higher prevalence of delusion of theft in the AD patients without a spouse who were cohabiting with their children may be explained by the fact that AD patients often live alone because their children usually go out in the daytime.
As for the premorbid personality traits, the AD patients with a neurotic personality showed significantly more frequent delusion of theft than the AD patients without a neurotic personality. The AD patients with a neurotic personality may more frequently put away things where they cannot be easily found, and/or, may more seriously worry about the place where important things are kept. Further studies about other personality traits including agreeableness, conscientiousness and openness to experience in the Big Five Personality Factors (Goldberg, Citation1990) are needed to clarify the correlation between premorbid personality traits and delusion of theft.
There were no significant differences in MMSE and HDS-R scores on generalized cognitive psychological tests between the two groups because severity of dementia was controlled to mild dementia by the CDR. In addition, there were no significant differences in neuropsychological cognitive sub-scales of COGNISTAT scores between the two groups. These results confirm the results of previous studies concerning the relations between delusion and neuropsychological cognitive functions (Burns et al., Citation1990; Ikeda, Citation2004; Migliorelli et al., Citation1995; Takechi et al., Citation2006).
Social cognitive functions construct representations of relationships between oneself and others, and cannot be generally assessed by neuropsychological cognitive tests (Adolphs, Citation2001). Some recent functional imaging studies have indicated the relations between social cognitive functions and the amygdala, medial prefrontal gyrus or superior temporal gyrus (Birbaumer et al., Citation1998; Gallagher et al., Citation2000; Grossman et al., Citation2000). Delusion, especially delusion of theft, is a psychiatric symptom with special reference to interpersonal relations, and may be related to social cognitive functions. The cognitive functions examined by the COGNISTAT include social cognitive functions beside neuropsychological cognitive functions such as memory, construction, calculation and language. In the present study, the AD patients with delusion of theft more frequently understood the interpersonal relation in the ‘speech sample’ of COGNISTAT than the AD patients without delusion of theft. This result suggests that mild AD patients without delusion of theft are more likely to have disturbance of social cognitive functions than mild AD patients with delusion of theft.
Most of the AD patients are likely to have some disturbance of social cognitive functions, although they often remain intact in AD patients with very mild dementia (Gregory et al., Citation2002). When AD patients cannot find lost things, those with relatively retained social cognitive functions may put the blame on others for lost things compared with the AD patients with disturbed social cognitive functions. The ‘Speech sample’ task used in the present study may not be an adequate indicator of social cognitive functions. However, other tasks used in previous studies for evaluation of social cognitive functions in non-demented elderly people (Maylor et al., Citation2002) and AD patients showing very mild dementia (the mean MMSE scores of 27.1) (Gregory et al., Citation2002) are difficult to apply to AD patients showing mild dementia. Further studies are needed to clarify the relation between social cognitive functions and delusion of theft using more appropriate tasks for AD patients.
There are some limitations in the present study. First, we should examine in detail the psychosocial factors such as the role of cohabiting family members in the care of AD patients, and the mechanism by which premorbid personality traits lead to delusion of theft. Second, the sample size was too small to do logistic regression analysis of psychosocial factors for generalization. Therefore, we could not discuss the inter-relationship among these factors. Third, cross-cultural studies about the relation between delusion of theft and psychosocial factors are needed in the future as the present study was performed using only Japanese AD patients.
Finally, the present study suggests the possibility of preventing and/or treating delusion of theft by psychosocial approaches. For example, it might be recommended that AD patients live with their family or enter an institution to treat delusion of theft for AD patients living alone. We often find that AD patients with delusion of theft do not show this delusion without medication after they enter a hospital. Further, psychosocial approaches considering premorbid personality traits of AD patients or maintaining their social cognitive functions are needed to prevent delusion of theft.
Acknowledgements
This study was supported by Grants-in-aid from the Research Support Foundation of Juntendo Institute of Mental Health.
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