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Prevalence of the core clinical features and the other neuropsychiatric symptoms in dementia with Lewy bodies

Patients with dementia with Lewy bodies (DLB) exhibit a wide variety of neuropsychiatric symptoms, and they cause a higher degree of caregiver distress. Previous studies revealed that hallucinations, misidentifications, and delusions in DLB symptomatologically and pathophysiologically differ. For example, although visual hallucination in a patient disappeared with administration of cholinesterase inhibitor, misidentification of persons might still continue in the same patient. Therefore, differentiation of the neuropsychiatric symptoms in DLB is essential to evaluate the response to treatments. Here, we present the detailed prevalence of neuropsychiatric symptoms of DLB based on a relatively large sample of patients. We examined outpatients who attended the Memory Clinic, Shiga Medical Centre, between July 2000 and March 2015. Two hundred and sixty DLBs (225 probable DLB and 35 possible DLB) were diagnosed according to the third consensus criteria. But four possible DLB patients had recurrent sleep talking (dream enactment behaviours while sleeping) which was suggestive of rapid eye movement sleep behaviour disorder (RBD), so these patients were classified as probable DLB according to the fourth criteria. Thus, 229 patients were diagnosed with probable DLB and 31 diagnosed with possible DLB. As diagnosis of DLB was not confirmed pathologically, only the probable DLB patients were included in the present study to increase the probability of correct diagnosis. The study protocol was approved by the Ethics Committee of Shiga Medical Centre. Psychiatric symptoms were classified based on a previous study, except that visual illusion was reassigned as a subclass of hallucinations. We judged parkinsonism as positive when one of the parkinsonian symptoms (rigidity, bradykinesia, and tremor) was present. The severity of parkinsonism was assessed using the simplified Unified Parkinson’s Disease Rating Scale part III (0 to 44). Cognitive fluctuation was assessed using the Mayo Clinic fluctuation scale. In addition to the analysis of the whole sample, we divided the patients into mildly and moderately impaired cognition groups, and compared the prevalence of symptoms between the two groups. We used the Mini-Mental State Examination (MMSE) level of 20/19 to divide the groups because the mean of the MMSE score was 19.9 and median of the MMSE was 20 for the whole sample. Continuous variables were compared by analysis of variance, and categorical variables were compared by Fisher’s exact test. The statistical threshold of P < 0.05 was used for the significance level. The results are shown in Table 1. In 229 probable DLB patients, 57 patients (24.9%) had all four core clinical features, 110 patients (48.0%) had three core features, and 62 patients (27.1%) had two core features. Among the core features, recurrent sleep talking was observed in 52.6% of patients with mildly impaired cognition and 62.4% of patients with moderately impaired cognition. In contrast, a previous study showed that sleep talking was observed in only 26.5% of advanced DLB patients (mean MMSE score = 10.1). These findings suggest that RBD is frequently seen in the early to moderate disease stage of DLB, and then decreases in the advanced stage of DLB. Misidentifications of persons, including the simple misidentification of persons, Capgras syndrome, phantom boarder, and reduplication of person, were occasionally observed even in mild DLB, and the prevalence significantly increased according to the progression of cognitive decline. This increase may be partly related to the progression of episodic memory impairment. A previous study suggested that impaired autobiographical memory and emotional function and their interactions, which were associated with dysfunction of the limbic-paralimbic systems, may underlie misidentifications in DLB. Persecutory delusions were found in 19.8% of mildly impaired DLB and in 33.0% of moderately