Death certification in treated cases of presenile Alzheimer's disease and vascular dementia in Scotland

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1 Age and Ageing 997; : - Death certification in treated cases of presenile Alzheimer's disease and vascular dementia in Scotland BRENDA M. THOMAS, JOHN M. STARR, LAWRENCE J. WHALLEY Department of Mental Health, University of Aberdeen, Aberdeen, UK 'Department of Geriatric Medicine, University of Edinburgh, Royal Victoria Hospital, Craigleith Road, Edinburgh EH DN, UK Address for correspondence: J. M. Starr Fax: (+) 57 5 Abstract Introduction: although death certification data are commonly used in dementia epidemiology, their reliability has been questioned. Methods: deadi certificates were available from the Registrar General for Scotland for all patients with Alzheimer's disease/presenile dementia (AD PSD) or vascular dementia (VaD) who had died in Scotland up until December 99. (immediate and underlying) and contributory causes of death were noted as well as place of death. Occupations of male patients were obtained from death certificates or from case notes and classified according to die Standard Occupational Classification. Bronchopneumonia was considered a non-specific cause of death and specific causes of deadi were classified as: cardiac disease, dementia, cerebrovascular disease, neoplasms, other vascular diseases and other diseases. Place of deadi was recorded as psychiatric hospital, district general hospital, nursing home or private residence. Results: death certificates of 98 people who had been treated for AD PSD and 8 who had been treated for VaD were identified. Bronchopneumonia was the most common immediate cause of deadi in the AD PSD group (7.9%) but less so for the VaD group (5.7%). For both groups place of death was associated with significant differences in pneumonia being reported as the immediate cause of death as well as specific underlying and contributory causes of deadi. Dementia was recorded for 9.5% of AD PSD patients but for only 97% of die VaD group. Conclusions: Scottish death certificate data significantly underestimate die prevalence of presenile VaD. Changes in patterns of institutional care may affect dementia rates estimated from deadi certificate data. Keywords: Alzheimer's disease, death certificates, presenile dementia, vascular dementia Introduction Causes of deadi routinely coded from deadi certificates are a readily accessible source of diagnostic data for epidemiological research. However, in studies of patients diagnosed as demented, investigators have found tiiat dementia was often omitted as eidier die underlying or contributory cause of deadi. Previous research has shown diat respiratory disease was die most common immediate cause in diose witii Alzheimer's disease (AD) [, ] and in tiiose widi vascular dementia (VaD) more deaths were due to cardiovascular disease []. Although mortality data are generally believed to underestimate dementia prevalence [, ], diese data are widely used in dementia research [5-7]. Several studies using death certificate data show regional differences in dementia mortality [8-] and, whilst some workers attribute these regional differences to environmental factors [9], odiers suggest that variation in deadi certification practices or diagnostic trends are largely responsible []. Similarly, recent increases in mortality from dementia reported in a number of countries [,, 7, ] are thought to relate more to increased awareness of dementing diseases and changes in deadi certification practices than to increased prevalence. The reliability of death certification diagnosis in patients widi dementia is most easily assessed in welldefined studies of patients widi a primary clinical diagnosis. Such studies are generally available from single centres. These studies, however, are open to bias due to local variations in bodi case selection and death Downloaded from by guest on 7 December 8

2 B. M. Thomas et al. certification practices. Furthermore, many studies are restricted to cases of AD with less attention paid to other diagnostic categories of dementia. We wished to investigate causes of death in a national study of treated cases of presenile AD (AD PSD) and VaD, independently diagnosed by standard clinical criteria [], to estimate the reliability of Scottish death certificate data and examine what factors determined the recording of dementia on death certificates. We reasoned that a national study would reduce the importance of local factors and chose our large sample to comprise presenile rather than senile cases to reduce co-morbidity (acknowledging the somewhat artificial distinction on age alone), so that dementia would be expected to have a major impact on the subjects' health. Subjects and methods We ascertained the treated incidence of AD PSD and VaD in Scotland as described previously [, ]. The Information and Statistics Division (ISD) of the National Health Service in Scotland provided data on all patients admitted to a psychiatric unit (97-88) aged less than 7 years, with a diagnostic code of AD, senile dementia, PSD, arteriosclerotic dementia, senile dementia with acute confusional state or dementia unspecified. We excluded dementia attributable to alcohol, head injury or Huntington's disease. Two trained raters examined the hospital records and included all patients with PSD in whom documented features of dementia were present before age 5 years. The criteria for AD suggested by McKhann et al [] and a Hachinski score [] were applied to each record. Patients were classified as having 'probable' AD PSD if they met the clinical criteria and had a Hachinski score of < 5 and VaD if they had a history of at least one cerebrovascular accident and a Hachinski score >. Death certificates were available from the Registrar General for Scotland for all AD PSD and VaD patients who had died in Scodand by December 99. (immediate and underlying) and contributory causes of death were noted as well as place of death. Occupations of male patients were obtained from death certificates or from case notes and classified according to the Standard Occupational Classification [5]. Female occupations were too rarely recorded to classify. Bronchopneumonia was considered a nonspecific cause of death and specific causes of death were classified (using a system adapted from Molsa et al []) into: cardiac disease, dementia, cerebrovascular disease, neoplasms, other vascular diseases and other diseases. Place of death was recorded as psychiatric hospital, district general hospital, nursing home or private residence. Each patient was also classified by health board of residence to allow examination of possible geographical variation of dementia recording on death certificates. Since pneumonia is a very common immediate cause of death for dementia patients [, ] this was not included in the statistical analyses of underlying and contributory causes of death but was separately related to other variables. In Scotland up to four causes of death are coded by the Registrar General. The most important underlying causes are followed by significant contributory causes. Only when pneumonia is the sole primary cause of death listed will this be the recorded underlying cause irrespective of a further contributory cause. Results We identified 79 cases of PSD in Scotland, of which 5 were 'probable' AD PSD and 8 were presenile VaD. The remainder comprised PSD patients who remained unclassified after investigation (n = 55) and further cases who had some features suggestive of AD PSD and were classified by us as 'broad' AD PSD in an earlier study []. Three hundred and ninety-eight ( male, 58 female) of the 5 AD PSD cases had died by December 99. Three hundred and seven died in psychiatric hospitals, in district general hospitals, seven in nursing homes and at private residences; place of death was not associated with any significant differences in age at symptom onset, presentation or death. Two hundred and eighty-two (7.9%) had pneumonia listed as the immediate cause of death; 8 (.9) had no additional underlying cause of death. In six cases pneumonia was the only cause of death recorded on the certificate. Cases with pneumonia listed as an immediate cause of death were not significantly older at symptom onset, presentation or death than cases where pneumonia was not listed as the immediate cause of death. Three hundred and sixty of the AD PSD cases (9.5%) had dementia listed as either a primary or contributory cause of death. Three hundred and forty-eight (8 male, female) of the 8 VaD cases had died by December 99:5 in psychiatric hospitals, 75 in district general hospitals, in nursing homes and 5 at private residences. Place of death was not associated with any significant differences in age at symptom onset, presentation or death. VaD cases were significantly less likely to have pneumonia listed as a primary cause of death compared with AD PSD cases (\ = 9.5, P<.) and less likely to have dementia mentioned on the death certificate (P<.). One hundred and eighty (5.7%) had pneumonia listed as the immediate cause of death; 8 (.%) had no additional underlying cause of death, hi nine cases pneumonia was the only cause of death recorded on the certificate. One hundred and seventy-three (97%) of the VaD cases had dementia listed as either a primary or contributory cause of death. Frequencies of underlying causes of death excluding pneumonia are shown by category in Table. Cause of death category was not associated Downloaded from by guest on 7 December 8

3 Death certification in presenile Alzheimer's disease Table I. Underlying causes of death in Alzheimer's presenile dementia and vascular dementia Cause of death Cardiac disease Dementia Cerebrovascular disease Neoplasms Other vascular diseases Other disorders No specific cause listed Total No. (and %) Alzheimer's presenile (.8) 8 (.) 9 (7-) 5 (.) 7 (.8) 9 (.) 8 (.) 98 with any significant differences in age at death, sex or socio-economic group for either AD PSD or VaD. There was no significant variation between the health boards in frequency of recording dementia for either AD PSD (x =.5) or VaD (* =.). We classified dementia reported on the death certificate as (i) AD, (ii) VaD (iii) Korsakoff s psychosis or (iv) non-specific dementia. For AD PSD cases, AD was recorded on (5.%) certificates, VaD on (-%) and non-specific dementia on 5 (.%). hi 8 cases (9.5%) dementia was not recorded on the death certificate. For VaD cases, AD was recorded on (.%) certificates, VaD on (.%), Korsakoff s psychosis on three (.9%) and non-specific dementia on (.5%). In 75 cases (5.%) dementia was not recorded on the death certificate. In this study of PSD (9%) of with AD PSD and (.8%) of 7 with VaD had dementia specified as 'presenile' on the certificate. One hundred and fourteen (7%) cases of AD PSD had 'senile' dementia recorded, of whom nine had died aged less than 5 years (Table ). In VaD, of the 5 (.%) cases recorded as having 'senile' dementia, had died before age 5 (Table ). For both AD PSD and VaD cases, place of death was associated with both a significant difference in pneumonia as a listed primary cause of death and significant 8 (.) (.) (.5) 7 (.) (9.) 98 Vascular 57 (.) 9 (8.) 5(.) (.) 5 (.) 5 (.9) 8 (.) 8 (.7) 5(.) (.7) 8 (.9) 7 (.) 8 (8.) 8 differences in specific cause of death categories listed for immediate and contributory causes of death (Table ). To elucidate the complex interactions between sex, diagnostic category, cause of death and place of death shown in Table, hierarchical log linear modelling was performed (Table ). This reveals that for sex and diagnostic category the second-order interaction between the two is more important than the effects of either taken alone. Three-way interactions do not contribute significantly to the model. Discussion In our national study of well-defined cases of PSD, dementia was recorded on the death certificate for over 9% of those with AD PSD but for less than 5% of those with VaD. As expected, bronchopneumonia was a common cause of death in AD PSD, but far less common for VaD. Diagnostic category was the most important determinant of cause of death as noted on the death certificate in simple models. However, hierarchical log linear modelling showed death certification to be more complex, with important secondorder interactions including both sex and place of death. With continuing reductions in mental hospital bed numbers, the effects of place of death on death Table. Contributory causes of death in Alzheimer's presenile dementia and vascular dementia Cause of death Cardiac disease Dementia Cerebrovascular disease Neoplasms Other vascular diseases Other disorders No specific cause listed Total Alzheimer's presenile (%) (.5) 59 (5.) (.5) (.5) (5.) 9 (7.) 98 (.) (.) (.) (.) (-) 7 (9.) 98 Vascular (%) (.7) (5.) 8 (8) (.) 5 (.) (.) 5 (.) 8 (.9) 7 (.9) (.) 5(.) (.7) 98 (85.) 8 Downloaded from by guest on 7 December 8

4 B. M. Thomas et al. Table. Place of death in Alzheimer's presenile dementia and vascular dementia: relationship to record of bronchopneumonia (pneu) as non-specific immediate cause of death and to underlying cause of death Place of death Alzheimer's presenile dementia Psychiatric hospital District general hospital Residential home Private address Underlying cause of death n Pneu Cardiac Dementia CVD Neoplasm Vascular Other Vascular dementia Psychiatric hospital District general hospital Residential home Private address CVD, cercbrovascular disease certification practice will confound estimation of changes in dementia prevalence over time from mortality statistics. Regional variations were not found within Scotland for these well-defined cases, but these may occur artefactually in the future if, for instance, per capita inpatient psychiatric services are reduced or more private nursing homes open in some areas than others. In a study of 7 AD PSD and 5 VaD deaths Newens et al [7] showed no significant difference in recording of dementia on death certificates between deaths in hospital and in the community. However, they do not specify the hospital type and do not subdivide place of death by dementia category. Martyn and Pippard [], in a study of 7 patients previously diagnosed with dementia, showed only % had dementia recorded as the certifying cause of death, while 57% had dementia mentioned in any section of the death certificate. They also found that those dying in mental hospitals (mostly long-stay patients) were more likely to have dementia recorded on the death certificate and, because patients are given the address of the institution after months residence, reported mortality in some areas was raised. Olichney et al [8] found die leading cause of death in a study of 97 people widi Alzheimer's disease was cardio-respiratory arrest. Dementia was recorded in over 75% of cases and, of these, the highest rate of reporting dementia was for those who died in nursing homes. This relatively high level of dementia reporting may reflect the enrolment of all the cases in an Alzheimer's Disease Research Centre where their condition was fully recognized. In a Table. Hierarchical log linear model of sex (SEX), diagnostic category (CATEG), underlying cause of death (COD) and place of death (PLACE) for 98 cases of presenile Alzheimer's disease and 8 cases of vascular dementia Effect name SEX by CATEG by COD SEX by CATEG by PLACE SEX by COD by PLACE CATEG by COD by PLACE SEX by CATEG SEX by COD CATEG by COD SEX by PLACE CATEG by PLACE COD by PLACE SEX CATEG COD PLACE Degrees of freedom Partial x P-value <.. <..7.8 <..7.7 <. <. Downloaded from by guest on 7 December 8

5 Death certification in presenile Alzheimer's disease community-based study of 8 AD and 5 VaD cases, Molsa et al. [] found that dementia was the underlying cause of death in 8% of AD and 8% of VaD patients, with pneumonia recorded as the most frequent immediate cause of death for both groups. Although we report death certificate findings from a large national sample, it is unclear whether our results are generalizable beyond the confines of Scotland since national coding practices vary widely. However, they confirm many of the conclusions of smaller, singlecentre studies and add support to the idea that caution is necessary when interpreting death certificate data. This study can only comment on well-defined dementia cases, but it is probable that less well-defined cases suffer from death certification inaccuracies to an even greater extent. Furthermore, there are limitations due to use of clinical criteria to define cases, particularly for VaD where the relationship between neuropathological findings and clinical presentation remains a matter of debate. All of those in the study sample were admitted to a psychiatric hospital at some stage in their illness but two further groups will not have been ascertained. The first of these is PSD patients admitted to psychiatric hospital but not reported to ISD: we have previously estimated this group as.5% for AD PSD [9]). The second is those never admitted to psychiatric hospital (estimated to be about % for AD PSD []). We conclude that our method detected about 9% of those with AD PSD who came to medical attention during our study period, but national reductions in bed numbers and increased provision of community care have substantially altered this proportion since 988. Our study reinforces the value of dementia case registers due to the unreliability of mortality statistics in these conditions. In summary, we found in Scotland that dementia was mentioned on most death certificates of people who had AD PSD, but was far less likely to feature for those with VaD. Thus, mortality statistics are likely to significantly underestimate VaD prevalence. We also found death certificate data to be inadequate for accurate diagnosis of specific dementia category. We note that changes in psychiatric inpatient service provision and private nursing home places are likely to affect the pattern of dementia death certification over the coming years. Key points Death certificate data significantly underestimate the prevalence of presenile vascular dementia. Changes in patterns of institutional care may affect dementia rates estimated from death certificate data. Acknowledgements This study was supported by a Medical Research Council grant (no. G899N). 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6 B. M. Thomas et al. 5. Office of Population Censuses and Surveys. Standard R. Death certificate reporting of dementia and mortality in an Occupational Classification. London: HMSO, 99. Alzheimer's Disease Research Center cohort. J Am Geriatr Soc. Molsa PK, Marttila RJ, Rinne UK Survival and cause of death in Alzheimer's disease and multhnfarct dementia. Acta Neurol Scand 98; 7: Newens AJ, Forster DP, Kay DWK. Death certification after a diagnosis of presenile dementia. J Epidemiol Community Health 99; 7: ; : 89 ' 9. McGonigal G, McQuade C, Thomas BM. Accuracy and completeness of Scottish mental hospital inpatient data. Hcalth BuU X " ' 8. Olichney JM, Hofsetter CR, Galasko D, Thai LJ, Katzman Received July 99 5O/: O9 " l ' Downloaded from by guest on 7 December 8