Department of Psychiatry, University of Leipzig, Germany
Correspondence: Steffi G. Riedel-Heller, Department of Psychiatry, University of Leipzig, Johannisallee 20, D-04317 Leipzig, Germany. Tel: +49-341-97 24 530; fax: +49-341-97 24 539; e-mail: ries{at}medizin.uni-leipzig.de
Declaration of interest Supported by Interdisziplinaeres Zentrum für Klinische Forschung (IZKF), University of Leipzig (01KS9504, project C7 79934700).
See part 2, pp.
255260, this issue.
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ABSTRACT |
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Aims To report and compare prevalence rates according to DSMIIIR and ICD10.
Method A population-based sample (n=1692, age 75+years) was investigated by a Structured Interview for Diagnosis of Dementia of Alzheimer Type, Multiinfarct Dementia and Dementia of other Aetiology according to DSMIIIR and ICD10 (SIDAM).
Results Whereas 17.4% (95% CI=15.9-19.5) of individuals aged 75+ years suffer from dementia according to DSMIIIR, only 12.4% (95% CI=10.6-14.2) are diagnosed as having dementia according to ICD10. The results revealed lower ICD10 rates in all investigated age groups. The largest differences appear in the oldest of the elderly.
Conclusions The ICD10 sets a higher threshold for dementia diagnosis. Larger differences in the eldest age groups might reflect difficulties in applying case definitions, especially in those beyond 90 years old.
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INTRODUCTION |
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METHOD |
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Instruments
A fully structured face to face interview was administered to the study
subjects by trained female physicians and psychologists at a home visit.
Cognitive function was assessed by the Structured Interview for Diagnosis of
Dementia of Alzheimer Type, Multiinfarct Dementia and Dementia of other
Aetiology according to ICD10 and DSMIIIR (SIDAM; Zaudig
et al,
1991a,b).
The SIDAM comprises a test performance part, a section for clinical judgement
and third party information to determine psychosocial impairment. The SIDAM
test performance part consists of a range of cognitive tests that constitute a
short neuropsychological battery with 55 questions, including all 30 items of
the Mini-Mental State Examination (MMSE;
Folstein et al, 1975).
The SIDAM gives detailed instructions about the application of the items. All
individuals interviewed face to face were asked to name an informant. If an
individual interviewed face to face scored below 24 on the MMSE (as
incorporated in the SIDAM test performance part) or reported impairment of the
activities of daily living that was not caused by physical or sensory
deficits, a comprehensive informant interview was conducted. Otherwise only
short informant interviews were applied. Deaf study participants were offered
a large print version of the interview. Blind study participants received test
versions without tasks involving eyesight and the final scores were projected.
In the case of sensory impairment, comprehensive informant interviews were
conducted. The SIDAM diagnostic algorithms were available to derive
ICD10 and DSMIIIR diagnoses of dementia. Consensus
conferences were held on each potential case to discuss the psychosocial
impairment. The interview contained further structured enquiries on
socio-demographic and other health aspects.
If relatives of study subjects refused participation on behalf of the
elderly person cared for or the study participant died between sampling and
planned examination, we offered the option of a fully structured proxy
interview. Instead of cognitive testing, the Clinical Dementia Rating Scale
(CDR) was used for assessment of cognitive function
(Hughes et al, 1982).
A very good agreement between the SIDAM-derived DSMIIIR
diagnosis for moderate and severe dementia had been shown in a sample of
n=180 (=0.83)
(Riedel-Heller et al,
2000). The prevalence results presented are based on those
individuals interviewed face to face. By including the respondents by proxy,
prevalence rates derived from face to face interviews increased
insignificantly by 1% for DSMIIIR and 1.4% for ICD10.
Testretest reliability was assessed in a sample of 30 subjects aged
75-99 years living in the community and in institutions. It was carried out by
two raters within a 1-week interval. Testretest reliability was found
to be excellent for SIDAM DSMIIIR diagnoses of dementia
(=1.00) and high for the severity level of dementia (
=0.94).
Similar results were found for SIDAM ICD10 diagnoses (
=1.00) and
the severity level of dementia (
=0.92).
The validity of dementia diagnosis was investigated using two strategies.
The first was to find out whether study participants were treated during the
past 5 years by checking the records of the two psychiatric hospitals in the
study area. Records of 34 participants in the field study were identified.
Although 32 were diagnosed with dementia in the field study, only 31 suffered
from dementia as diagnosed by the clinicians. The discordant case suffered
from depression. However, agreement between clinical and field diagnosis was
found to be good (=0.78). The second strategy involved a subsample of
the study participants (n=74) being thoroughly investigated
clinically: physical and neurological status, cognitive testing,
electroencephalogram, brain imaging and blood test. The agreement was found to
be very good (
=0.85).
Analysis
Frequency of dementia is described in terms of percentage prevalence.
Confidence intervals were calculated based on binomial distribution. Owing to
multiple comparisons using the 2 test, the level of
error was adjusted to 0.01.
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RESULTS |
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Of the study participants interviewed face to face, 17.4% (95%
CI=15.9-19.5) suffered from dementia according to DSMIIIR. This
includes mild, moderate and severe cases. Age- and gender-specific prevalence
rates are summarised in Table
1. Up to age 89 years the prevalence rates for women and men do
not differ significantly. Almost half of the dementia cases (42.7%) have mild
dementia and over a quarter have moderate (29.1%) and severe (28.2%) dementia.
According to the severity rating, there is no statistical difference between
the age groups (2=6.1584, d.f.=8, P=0.629).
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Dementia according to ICD10 was diagnosed in 12.4% (95%
CI=10.6-14.2) of the study participants interviewed face to face. Age- and
gender-specific prevalence rates are shown in
Table 2. Prevalence rates for
men and women do not differ significantly; 19.7% of the study participants
suffering ICD10 dementia have mild dementia, 40.8% have moderate
dementia and 39.5% have severe dementia. Regarding the severity rating, there
were no statistical differences found in the age groups
(2=6.6317, d.f.=8, P=0.577).
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Figure 1 compares age-specific prevalence rates of dementia according to DSMIIIR and ICD10. The comparison of DSMIIIR and ICD10 rates indicates that dementia prevalence increases with age regardless of the classificatory system used. Beyond age 95 years the curve levels off. This trend is observed in both DSMIIIR and ICD10 rates but it is more obvious using ICD10. Also, dementia prevalence rates according to ICD10 are lower than dementia according to DSMIIIR in all the investigated age groups. The largest differences appear in the eldest age groups.
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Finally, detailed analysis of dementia prevalence according to DSMIIIR and ICD10 in the mild, moderate and severe severity stages shows that DSMIIIR and ICD10 differences are based solely on different judgements of mild dementia cases (see Table 3). Using DSMIIIR, individuals are included in the mild dementia category who do not get a dementia diagnosis according to ICD10.
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DISCUSSION |
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Figure 2 shows age-specific prevalence rates of recent field studies considering more than three age groups and applying DSMIIIR for case definition compared with the LEILA75+ results (Rocca et al, 1990; Letenneur et al, 1993; Roelands et al, 1994; Lobo et al, 1995; De Ronchi et al, 1998; Ott et al, 1995). Up to age 89 years the LEILA75+ results correspond with the results of the studies reviewed. Beyond 90 years the LEILA75+ prevalence rates exceed the rates found in these studies. A similar pattern emerges when our results are compared with the EURODEM pooled findings of 12 studies (age 75-79 years, 5.7%; 80-84 years, 13.0%; 85-89 years, 21.6%; 90-94 years, 32.2%) (Hofman et al, 1991). However, mild dementia cases were only partially included in the EURODEM studies.
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Figure 2 illustrates that results differ, especially in the eldest age groups. This points to difficulties in applying criteria for case definition in this population segment, where cognitive deficits often are accompanied by physical and sensorial impairment. This makes it difficult to tease apart psychosocial impairment owing to cognitive deficits or other reasons. The SIDAM includes 14 questions enquiring about impairment of activities of daily living owing to cognitive deficits. These questions have to be answered by caregivers. Therefore, it is not surprising that our results correspond much better with the results of the Munich study of the oldest of the elderly using SIDAM as the method of case identification (Fichter et al, 1995). For individuals aged 90+ years the Munich study reported SIDAM DSMIIIR rates of 40.2%. Clinical diagnoses also were determined, yielding an even higher rate (57.3%).
Dementia according to ICD10
Compared with DSMIIIR, ICD10 criteria for dementia
appear to be more restrictive. The ICD10 requires (G11) memory decline
and (G12) a decline in other cognitive abilities sufficient to impair personal
activities of daily living. The awareness of the environment has to be
preserved (G2). A decline in emotional control or motivation or a change in
social behaviour has to be established (G3). The criterion G1 should have been
present for at least six months (World
Health Organization, 1994).
Therefore, it is not surprising that our results show a lower prevalence according to ICD10 compared with DSMIIIR. The DSMIIIR includes cases that are not considered to have dementia according to ICD10. Our data show that this is owing to the ICD10 criterion that requires a decline in emotional control or motivation or a change in social behaviour, which is not an obligatory criterion in DSMIIIR. There are individuals who are mildly cognitively impaired but do not show these changes, or these disturbances might not be recognised or reported by caregivers, probably owing to negative age stereotypes. However, this constellation is found mainly in the eldest age groups, where the largest differences in the prevalence rates on comparing both classification systems were found.
Comparison of ICD10 and DSMIIIR dementia
rates
To our knowledge, only two studies have reported ICD10 and
DSMIIIR rates. They confirm lower rates by applying ICD10
criteria. The Munich study of the oldest of the elderly (age groups 85-89
years and 90+ years) yielded prevalence rates according to SIDAM ICD10
of 13.6% (95% CI=9.3-17.9) and 24.0% (95% CI=14.3-33.7), respectively
(Fichter et al, 1995). Despite using the same method for case identification, the rates are lower
than those reported in our study. The Australian study reported even lower
prevalence rates by applying ICD10 criteria strictly (age 75-79 years,
1.2%; age 80-84 years, 5.2%; 85+ years, 10.3%)
(Henderson et al,
1994). However, the authors explicitly mention that their results
are not representative owing to a lack of informant information on a
substantial number of participants. The authors concluded that ICD10
criteria proved to be demanding to apply in community surveys because they are
more dependent on reliable information from informants. This corresponds to
our experience and refers especially to the judgement of decline of emotional
control or motivation or a change in social behaviour in the oldest of the
elderly.
Dementia prevalence in the oldest of the elderly
Despite the mentioned difficulties in applying case definitions in the
oldest of the elderly, our results suggest that prevalence rates of dementia
do not increase exponentially beyond age 90 years, rather they level off. Few
recent studies show how prevalence rates perform in individuals aged 90 years
and over. Our results are in line with what was found by Heeren et al
(1991), Reischies et
al (1997) and by a
meta-analysis conducted by Ritchie & Kildea
(1995). However, the majority
of studies revealed contrasting results, suggesting further increasing
prevalence rates in the oldest of the elderly
(Graves et al, 1996;
von Strauss et al,
1999; Ebly et al,
1994; Fichter et al,
1996; Blansjaar et al,
2000).
We argue that the performance of prevalence of dementia diagnosis in the oldest of the elderly will remain unclear as long as substantial methodological difficulties exist in determining dementia in the oldest of the elderly. However, epidemiology of dementia in the oldest of the elderly is of great interest because there are practical consequences pertaining to the planning of health services and conceptual consequences regarding the question of whether dementia is an inevitable result of ageing or a disorder occurring within a specific age range (ageing- v. age-related).
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Clinical Implications and Limitations |
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LIMITATIONS
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Received for publication September 21, 2000. Revision received February 16, 2001. Accepted for publication February 16, 2001.
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