METHODS

The Kuopio 75+ study is a population based health survey focused on the clinical epidemiology of diseases, especially those causing dementia, and on functional capacity in elderly people aged 75 years or more. A random sample of 700 subjects was drawn from the total population of people born before 1 January 1923 and living in the city of Kuopio (population 80 000) in eastern Finland, on 1 January 1998 (n = 4518) (fig 1 and table 2). In all, 601 subjects (86% of the random sample) were available in 1998 for a structured clinical examination and an interview by a geriatrician (AV) and a trained nurse. Ninety nine subjects could not be examined (79 refused, five could not be contacted, and 15 died before the examination).

• Download figure
• Open in new tab
• Download powerpoint

Figure 1

Flow chart of the study.

The structured interview included items concerning sociodemographic factors, living conditions, social contacts, health behaviour, and physical health. The overall physical and neurological status was examined. The study protocol included basic laboratory tests and chest x ray. Patients were also referred for further examination and imaging if warranted by their clinical condition. All medical records from the municipal health centre and from local hospitals and Kuopio University Hospital were evaluated. In addition, interviews were carried out with family members and staff in health and social care if the subject was unable to give information, needed health and social services, or lived in an institution.

A history of cognitive decline was obtained by interviewing the subject and relatives and other people who knew the subject, and from all the medical records. The behavioural and psychiatric symptoms of demented patients were obtained from the relatives or care giving personnel whenever possible, as well as from the interview and examination. The diagnosis of dementia was based on DSM-IV criteria.¹⁴ Dementia was rated as mild, moderate, or severe according to the guidelines in DSM-III-R.¹⁵ Dementia with Lewy bodies was clinically diagnosed according to the consensus criteria by McKeith et al (1996)¹ (table 1). Alzheimer’s disease (all probable cases), vascular dementia, and dementia caused by other general medical conditions were diagnosed according to the DSM-IV criteria.¹⁴ All dementia diagnoses were subsequently evaluated by a neurogeriatrician (RS). The clinical diagnosis of dementia was established and the type and stage of the dementia were determined in consensus meetings, using all the data available.

Detection of the clinical features of DLB was based on a physical examination by the geriatrician and on information from the medical records, the subjects, relatives, and other people who knew the subject. Extrapyramidal symptoms were considered present when at least two of the following features were detected or reported in medical records: tremor at rest, rigidity, bradykinesia, or snuffling gait. Additionally, the presence of extrapyramidal symptoms required the exclusion of possible neuroleptic drug treatment as the cause of the symptoms.

The main criterion used to differentiate DLB and Parkinson’s disease with dementia was the temporal relation of the appearance of the cognitive symptoms and extrapyramidal symptoms. If extrapyramidal symptoms were detected at least one year before the cognitive decline, the diagnosis of Parkinson’s disease with dementia was made.^1,16 The diagnosis of depression was made according to the DSM-IV criteria (proxies were interviewed in cases of dementia).¹⁴

The activities and instrumental activities of daily living were assessed with the Barthel index of ADL¹⁷ and the IADL scale,¹⁸ respectively. The mini-mental state examination test (MMSE)¹⁹ was used to screen cognitive capacity.

Ethical issues

Written informed consent for the study was obtained from subjects or their relatives. The ethics committee of the Kuopio University Hospital approved the study.

Statistical analyses

Statistical analyses were made with SPSS for Windows 9.0. Student’s t test for continuous variables and χ² test for nominal variables were used when comparing groups. The 95% confidence intervals (CI) of prevalence rates were calculated.

RESULTS

A dementia disorder was diagnosed in 137 subjects, giving a prevalence of 22.8% (95% CI 19.4% to 26.2%) among the persons aged 75 years or older (table 3). Dementia with Lewy bodies was found in 30 subjects, with a prevalence of 5.0% (3.2% to 6.7%). Probable DLB was diagnosed in 20 subjects (3.3% (1.9% to 4.8%)) and possible DLB in 10 subjects (1.7% (0.6% to 2.7%)). Alzheimer’s disease was diagnosed in 64 subjects, with a prevalence of 10.6% (8.2% to 13.1%). Vascular dementia was diagnosed in 32 subjects, with a prevalence of 5.3% (3.5% to 7.1%).

Among the demented subjects, dementia with Lewy bodies comprised 21.9% (15.0% to 28.8%) of cases, Alzheimer’s disease, 46.7% (38.4% to 55.1%), and vascular dementia, 23.4% (16.3% to 30.4%). Table 4 shows the clinical diagnostic features of subjects with DLB according to the consensus criteria of McKeith et al.¹

Other dementing disorders (n = 11, 8% of the demented subjects) included two cases of normal pressure hydrocephalus, two cases of Parkinson’s disease with dementia, two cases of alcohol related dementia, one case of meningioma, two cases with schizophrenia with dementia, one case of frontotemporal dementia, and one case with severe dementia of unknown cause.

DISCUSSION

A random sample of all the elderly citizens aged 75 years or older from the city of Kuopio on 1 January 1998 was used in this study. In all, 601 subjects (86% of the random sample) were examined. Those who did not participate in the study did not differ from participants in their sex distribution, but they were a little older than the participants. All the non-participants lived in the community.

The prevalence of dementia of 23% in a population aged 75 years or older is slightly higher than the values of 4.2–15.6% found in previous population based studies in Europe and the USA.^20–28 A possible reason for the higher prevalence in our study might be the bias caused by the non-participants living in the community, who were less likely to be demented than patients living in institutions. However, the prevalence of dementia is 19.6% when calculated for the whole population sample drawn in our study.

The prevalence of DLB was 5.0% (95% CI, 3.2% to 6.7%), comprising 22% of the demented subjects. The prevalence of probable DLB was 3.3% (15% of all demented subjects) and of possible DLB, 1.7% (7% of all demented subjects). In the recent studies, the prevalences of DLB have been much lower.^11–13 However, the age of the population in our study was older.

The clinical diagnosis of DLB was based on the clinical examination (lasting one to two hours per patient), on the information from the patients’ proxies, and from all the medical records available. The reliable identification of fluctuating cognitive function and confusion, one of the key diagnostic features in DLB, was the major source of diagnostic difficulty in our study. DLB is often underdiagnosed, especially in subjects living alone. The use of neuroleptic drugs (low doses of neuroleptics were used regularly or occasionally by 18 patients with DLB) may have had an effect on the severity of extrapyramidal symptoms, though spontaneous symptoms of parkinsonism were also reported previously in these cases. In the prospective study by McKeith et al,⁷ the major difficulties were in the detection of visual hallucinations and parkinsonism. However, when the consensus criteria are employed in the diagnosis of DLB, good diagnostic specificity and inter-rater reliability can be achieved.^2,7 The criteria have been reported to be less useful for identifying cases in clinical settings (relatively low sensitivity), although when the diagnosis is made it is likely to be correct.^29,30

In our study, more subjects with DLB lived in the community, were at a less severe stage, and had shorter duration of the dementing disorder than subjects with other types of dementia. One possible explanation for these differences may be the difficulties in differentiating the subtypes of dementia in the most severe cases. At the severe stage of dementia, the clinical features of Alzheimer’s disease are remarkably similar to those of DLB. Subjects with DLB might also die earlier in the course of dementia than patients with other dementias.

In our study we described the clinical features of the DLB patients examined. However, mixed pathologies in DLB and Alzheimer’s disease are common according to published reports.^4,7,10,31 The proportion of subjects with clinically diagnosed DLB who were actually suffering from neuropathologically pure DLB in our study remains unclear.

Conclusions

The prevalence of the disorder fulfilling the clinical diagnostic criteria of DLB was high, at 5%, in a general population aged 75 years or older, and 22% among all patients with dementia. As we lack a prospective follow up of the subjects, we may assume that our figures represent an underestimate of the true frequency of DLB symptoms.