Urban Community Dementia Service, Kochi
Memory Clinic, Department of Neurology, Indira Gandhi Cooperative Hospital and Medical College, Kochi
Mandiram Hospital, Kottayam, India
Correspondence: Dr S. Shaji, Bethsada Hospital, Vengola PO, PIN 683 554, Ernakulam District, Kerala, India
Declaration of interest None. Funding detailed in Acknowledgements.
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ABSTRACT |
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Aims To investigate the prevalence, psychosocial correlates and risk factors of various dementing disorders in an urban population in Kerala, southern India.
Method A door-to-door survey was conducted in the city of Kochi
(Cochin) to identify residents aged 65 years using cluster sampling. Of
1934 people screened with a vernacular adaptation of the Mini-Mental State
Examination, all those scoring at or below the cut-off of 23 were evaluated
further and those with confirmed cognitive and functional impairment were
assigned diagnoses according to DSM-IV criteria. Identified cases were
categorised by ICD-10 criteria. Ten per cent of those screened as negative
were evaluated at each stage.
Results Prevalence of dementia was 33.6 per 1000 (95% CI 27.3-40.7). Alzheimer's disease was the most common type (54%) followed by vascular dementia (39%), and 7% of cases were due to causes such as infection, tumour and trauma. Family history of dementia was a risk factor for Alzheimer's disease and history of hypertension was a risk factor for vascular dementia.
Conclusions Dementia is an important health problem of the elderly population. Identification of risk factors points towards the possibility of prevention.
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INTRODUCTION |
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METHOD |
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The list of voters and the area map constituted the sampling frame. The Ernakulam constituency is divided into 178 parts, each of which has a population of 800-1000. For operational purposes, each part was designated as a cluster, and a cluster sampling technique was used. Thirty of 178 parts were randomly selected and in each a door-to-door survey was conducted to identify residents aged 65 years and above. The community survey was conducted by a group of six psychiatric social workers who were trained by a psychiatrist (S.S.). They explained the purpose and procedures of the study to the family members and obtained their informed consent.
Assessment tools
The following measures were used.
Mini-Mental State Examination
The Mini-Mental State Examination (MMSE;
Folstein et al, 1975)
was used as a screening test for cognitive impairment. Three primary
translators (two psychiatrists and a clinical psychologist), well versed in
English and Malayalam, translated the original version into Malayalam
independently. They then met to compare the versions item by item and agree
upon a final version. This version was used to test a sample of 20 literate
and 20 illiterate people from different socio-economic strata. These people
were asked whether the items were clear and simple, and some minor changes
were made in the translation in response to their feedback. Two bilingual
experts then back-translated the vernacular version into English to establish
linguistic equivalence. The primary translators and the back translators met
and discussed the questionnaire item by item to ensure the translations
approximated as closely as possible. The correlations between English and
vernacular scores were found to be high. The interrater reliability
coefficient was found to be 0.9. Sensitivity and specificity for various MMSE
scores were checked against the diagnosis of dementia according to DSM-III-R
criteria (American Psychiatric Association,
1987). A cut-off score of 23 was selected with a sensitivity of
88% and specificity of 82% (Shaji et
al, 1996).
CAMDEX Section B
Section B of the Cambridge Mental Disorders of the Elderly Examination
(CAMDEX; Roth et al,
1986) was used for cognitive examination. The test was translated
into the vernacular and items were modified and selected after field trial, to
harmonise with the sociocultural situation. The interrater reliability
coefficient was found to be 0.8. Separate cut-off scores were selected for
different educational levels: a cut-off of 72 was selected for people who were
literate, with a sensitivity of 94% and specificity of 90%, and a score of 52
was selected for those who were illiterate, with a sensitivity of 98% and
specificity of 88% (Shaji et al,
1996).
CAMDEX Section H
Section H of the CAMDEX (Roth et
al, 1986) is a structured interview in which information
about an individual's history and functional abilities is obtained from a
relative or caregiver. This interview elicits details of personal and social
functioning as well as the individual and family histories.
Socio-economic Status Scale - Urban
The Socio-economic Status Scale - Urban
(Kuppuswamy, 1976) was used to
categorise the population into different socio-economic groups.
Study design
The study was conducted in three phases. During phase I, all identified
people aged 65 years and above were screened with the vernacular adaptation of
MMSE. The screening was done by trained psychiatric social workers. In phase
II, those who scored 23 or below on the MMSE had a detailed neuropsychological
evaluation with CAMDEX Section B to confirm the impairment in cognitive
function. For each individual a caregiver or relative was interviewed with
CAMDEX Section H to confirm the history of deterioration in social and
occupational functioning or activities of daily living. This was done by a
clinical psychologist. In phase III, a psychiatrist visited the homes of
participants whose impairments were confirmed by the CAMDEX Sections B and H
for diagnostic evaluation according to DSM-IV criteria
(American Psychiatric Association,
1994). Ten per cent of the negatively screened population were
randomly selected and evaluated at each stage. Evaluation in phase III
included a detailed medical history, physical and neurological examination.
Necessary investigations were done to rule out conditions such as
hypothyroidism, HIV infection, brain tumours and vitamin B12
deficiency. Cases of dementia were categorised according to ICD-10 criteria
(World Health Organization,
1992). Although DSM-IV is more specific in the definition of
domains of impairment required for the diagnosis of dementia, ICD-10 criteria
offer clear guidelines for categorising the cases.
Age- and gender-specific prevalence rates of dementia, Alzheimer's disease and vascular dementia were calculated. The Alzheimer's disease group and the vascular dementia group were compared with control groups matched for age, gender and education and with one another on various socio-demographic and clinical parameters. Assessment of risk factors was based on the structured interview in CAMDEX Section H. Caregivers were asked whether the individual had a known history of high blood pressure, diabetes mellitus, cardiac disease, cancer, Parkinson's disease, Down's syndrome, head injury, fits or any psychiatric disorder. The caseness of alcoholism was assessed with questions about alcohol consumption and problems related to the individual's drinking habits.
The control groups were selected by group matching of the cases with respect to age, gender and level of education. For this purpose the entire population was stratified according to these categories and the required number of controls were selected from each group at random.
The group comparisons were made using the chi-squared test. Fisher's exact test was used to find out the statistical significance whenever the expected frequency was less than 5. Odds ratios were used to find out the relative risk of various risk factors pertaining to dementia and 95% confidence intervals were determined using the approximation of the Woolf formula.
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RESULTS |
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Of the 1934 people screened with MMSE, 327 scored at or below the cut-off score of 23. The clinical psychologist approached these 327 people for neuropsychological evaluation with CAMDEX Section B. Twenty-seven of them could not be tested: 7 people refused to consent, 5 had died, 8 were bedridden owing to physical illness and 7 could not be traced. Historical evaluation of these cases by the clinical psychologist indicated that no one in this group had a history suggestive of dementia. Caregivers of the 223 people with cognitive impairment confirmed by CAMDEX Section B assessment were interviewed using CAMDEX Section H, leading to identification of impairment in social and personal functioning in addition to cognitive impairment, 55 of whom were diagnosed as having dementia based on DSM-IV criteria. Among the negatively screened cases, 161 people out of 1607 with an MMSE score above the cut-off of 23 were evaluated with CAMDEX Section B, and one case of dementia was identified; in the subsequent phase of negative screening no case could be detected.
Of the 223 people with cognitive impairment, 127 had no impairment in social or occupational functioning. This group comprised 31 men and 96 women (mean age 74.5 years, s.d.=7.2; mean MMSE score 21, s.d.=0.2); 60 were illiterate and 33 had only primary education.
Forty-one people had cognitive impairment along with impairment in social and occupational functioning but did not meet the criteria for a diagnosis of dementia. In this group there were 13 men and 28 women (mean age 78.3 years, s.d.=4.8; mean MMSE score 17, s.d.=5.24); 20 were illiterate, and 32 belonged to lower-class or lower middle-class households. Most of the people of this group had multiple disabilities due to sensory impairments, physical diseases and psychiatric disorders; 19 people had visual impairment, 8 had hearing problems and 5 had both. The reported physical diseases included hypertension (41.5%), diabetes mellitus (36%), cardiac disease (24%), arthritis (19.5%), stroke (14.6%) and other diseases such as bronchial asthma, tuberculosis and malignancy. Seven people had psychiatric disorders: 5 had depressive disorder, 1 had bipolar mood disorder and 1 had schizophrenia; 5 had age-related cognitive decline.
One case of dementia was detected while evaluating the 10% of the negatively screened population, so we might have missed 10 cases of dementia in the group of people who scored above the cut-off on the MMSE; 65 cases of dementia could have been detected in 1934 elderly people aged 65 years and above, yielding a prevalence rate of 33.6 per 1000 (95% CI 27.3-40.7).
Categorisation of the 56 cases of dementia by ICD-10 diagnostic criteria showed that 30 (54%) were due to Alzheimer's disease, 22 (39%) were due to vascular dementia and 4 (7%) were due to other causes (1 case of tuberculous infection, 1 case of head trauma and 2 cases of cerebral tumours). Age- and gender-specific prevalence rates of dementia are given in Table 2.
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Alzheimer's disease was found to have a prevalence rate of 15.5 per 1000 (95% CI 9.6-20). This form of dementia was found in 13 men and 17 women (ratio 1:1.3). The mean age of onset of illness was 74.5 years (s.d.=9) and mean duration of illness was 4.07 years (s.d.=3) according to clinical evaluation done by the psychiatrist. The medical history revealed that 21 out of 31 persons were receiving medical treatment.
The prevalence of vascular dementia was 11.4 per 1000 (95% CI 6.7-16.1). Of
the 22 persons in the vascular dementia group, 6 were women and 16 were men
(1:2.7). There was a male preponderance of vascular dementia
(2=4.45, P<0.05). The mean age of onset of illness
was 70 years (s.d.=7.5) and the mean duration of illness was 4.3 years
(s.d.=4); 21 out of 22 persons were receiving medical treatment.
Comparison of the Alzheimer's disease group (n=30) with a control group matched for age, gender and education (n=30) revealed that a family history of dementia was a significant risk factor for developing Alzheimer's disease (OR 12.43, 95% CI 1.46-105.6). Comparison of the vascular dementia group (n=22) with a control group (n=22) revealed that people with a history of hypertension had an increased risk of developing vascular dementia (OR 11.8, 95% CI 2.48-49.5).
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DISCUSSION |
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Rural v. urban prevalence
The prevalence rate obtained from this urban study was lower than that
found in an earlier rural study in which the prevalence of dementia in people
aged 65 years and above was 44 per 1000
(Shaji et al, 1996).
Comparison of the prevalence rates of dementia in these rural and urban
populations indicates that there is little variation in the prevalence of
Alzheimer's disease (15.5 per 1000 in the urban population and 17 per 1000 in
the rural population), but that the higher prevalence of vascular dementia
contributes to the greater total prevalence in the rural community.
Rajkumar & Kumar (1996) reported a higher prevalence of dementia in the rural community than in urban settings. Shibayama et al (1986) also found higher prevalence rates of dementia in rural areas of Japan compared with urban areas. Differences in lifestyle, health awareness and healthcare delivery systems may be the factors contributing to this difference. Moreover, people in urban areas are better educated and more in touch with current events, and so perform better on cognitive testing.
Dementia subtypes
In rural Kerala vascular dementia constituted 58% of the total dementia
cases (Shaji et al,
1996). In studies conducted in rural and urban communities in
Tamil Nadu, a neighbouring state to Kerala, vascular dementia constituted 27%
and 26% respectively of the total dementia cases
(Rajkumar & Kumar, 1996).
It has been observed that there is a regional variation in the relative
proportion of Alzheimer's disease and vascular dementia. The relative
proportion of Alzheimer's disease in the Indian studies ranged from 41% to 65%
and the proportion of vascular dementia ranged from 22% to 58%
(Rajkumar & Kumar, 1996;
Shaji et al, 1996;
Vas et al, 2001).
Risk factors
One of the consistent findings across studies is that the prevalence of
dementia increases proportionately with age. Our study confirmed this finding.
We also found that people with Alzheimer's disease more often had an increased
family history of dementia. Increased risk of dementia among first- and
second-degree relatives has already been reported
(Heston et al, 1981;
Whalley et al, 1982;
Heyman et al, 1984).
Identification of hypertension as a risk factor for vascular dementia
indicates the need for changes in lifestyle and better monitoring of blood
pressure.
Methodological issues
In our study 127 people had cognitive impairment without any impairment in
social and occupational functioning; the mean MMSE score of this group was 21.
Of these 127 people, 100 had MMSE scores ranging between 20 and 23. A
borderline score on the MMSE may not indicate true organic impairment, but may
be due to other factors (such as motivational and emotional factors,
depression, sensory impairments, motor slowness and general physical frailty)
that affect the test performance.
Although 96 people had confirmed cognitive impairment along with functional impairment, only 55 people satisfied the DSM-IV criteria for dementia. The 41 people who did not meet these criteria need special mention. They had neither a clinical history nor signs and symptoms suggestive of dementia. Normality, cognitive impairment and dementia are part of a spectrum; there is no fixed point at which normality stops and dementia supervenes. It was apparent that there was an accumulation of factors in this group that adversely affected cognitive functioning. The possibility of missing some cases of dementia in this group cannot be fully ruled out, so the reported prevalence may be a slight underestimation. It is possible that some people in this group might develop clinical dementia subsequently.
The study investigated a population of comparatively high literacy (89%), which facilitated age ascertainment and cognitive testing. Analysis of the results did not reveal any relationship between literacy and diagnosis of dementia. Selection of 65 years as the lower age limit made the study design more efficient.
The problem of diagnostic misclassification between Alzheimer's disease and vascular disease is one of the problems of dementia research. Compared with DSM-IV, the ICD-10 criteria offer more promise of specificity of diagnosis, but no comparative study of diagnostic accuracy is available (Cummings & Khachaturian, 1999). Although diagnostic accuracy has not been adequately assessed for cases categorised during the course of a community survey, it would probably be lower than that for referred cases. The assessment of risk factors was based on the interview with a caregiver, and this is one of the limitations of the study.
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Clinical Implications and Limitations |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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Received for publication January 19, 2003. Revision received August 10, 2004. Accepted for publication August 11, 2004.