REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER TO BIRTH YEAR 1999

Transcription

1 REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER TO BIRTH YEAR 1999 TELETHON INSTITUTE FOR July 2006 Child Health Research

2 Acknowledgements We are very grateful to the NHMRC who currently fund this work and the other funding bodies (see Funding p2) who have supported the Register since its inception. Our special thanks go to the many health professionals who provide all information held on the Register and to the service agencies that have assisted and encouraged this research undertaking over the years. Our work would not be possible without their help. We are particularly grateful to the therapists in the country centres whose responses to our annual requests are essential to the completeness and accuracy of the Register. The Register would be of little use without information on births and deaths throughout the State which make up our comparison population data. This is provided by the Registrar General of Western Australia from birth and death certificates, also by Vivian Gee, Coordinator of the Midwives Notification of Births System at the Health Department of Western Australia. We are grateful to all midwives who contribute to this high quality data collection which greatly enhances our ability to study maternal, obstetric and perinatal factors in relation to cerebral palsy. We also gratefully acknowledge the members of our Advisory Committee for their continued support over the years, our Honorary Consultants who have guided our decisions and research directions, the late Dr Louisa Alessandri for her valuable assistance, and the many other people, too numerous to mention individually, who have been responsible for improving the data held on the Register and our ability to use it. Last, but certainly not least, a very big thanks to Heather Monteiro for the design and development of this Report.

3 REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER TO BIRTH YEAR 1999 Linda Watson Eve Blair, PhD Fiona Stanley AC FAA, FASSA, MBBS, MSc, MD, FFPHM, FAFPHM, FRACP, FRANZCOG, Hon DSc, Hon DUniv, Hon FRACGP, Hon MD, Hon FRCPCH Telethon Institute for Child Health Research PO Box 855 West Perth, Western Australia 6872 AUSTRALIA

4 THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER Principal Investigators: Associate Investigators: Research Officer: Research Assistant: Computer programmers: Honorary Consultant: Genetic Consultant: Advisory Committee: Professor Fiona Stanley Associate Professor Eve Blair Dr Beverly Petterson Dr Nadia Badawi Dr Jennifer Kurinczuk Dr Karin Nelson Ms Jan de Groot Ms Linda Watson Mr Peter Cosgrove Ms Margaret Wood Mrs Brenda Lake Dr Jennie Slee Dr Peter Chauvel Dr Noel French (Chairperson) Dr Rex Henderson Dr Athel Hockey Dr Lakshmi Nagarajan Mrs Kerry Naso (Consumer representative) Dr Trevor Parry Dr Beverly Petterson Dr Jon Silberstein Dr Peter Silberstein Mrs Margaret Tait (Consumer representative) Dr Jane Valentine Dr Ian Walpole Dr Peter Walsh 2... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

5 CONTENTS Acknowledgements Introduction Funding Aims of the WA Cerebral Palsy Register The Australian Cerebral Palsy Register Methods Defi nition Data collection Record linkage Denominators Classifi cation system Confi dentiality of data Ethical considerations Current projects International developments Results Overall birth prevalence Section I: Pre- and neonatally Acquired Cerebral Palsy Gender of infant Birth weight and gestational age Plurality Area of residence Indigenous status of mother Age of mother Previous births Severity of cerebral palsy Type of cerebral palsy Associated disabilities: (1) Intellectual disability (2) Epilepsy, blindness, deafness and lack of speech Age at recognition of cerebral palsy REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER... 3

6 Section II: Postneonatally Acquired Cerebral Palsy Trends in postneonatally acquired cerebral palsy Gender Area of residence Indigenous status of mother Age of mother Severity of cerebral palsy Type of cerebral palsy Associated disabilities (1) Intellectual disability (2) Epilepsy, blindness, deafness and lack of speech Postneonatal causes of cerebral palsy Postneonatal causes by indigenous status Postneonatal year of acquisition of cerebral palsy References APPENDICES APPENDIX A: Notifi cation card APPENDIX B: Data collection form APPENDIX C: Description of cerebral palsy APPENDIX D: Gross Motor Function Classifi cation System APPENDIX E: Manual Ability Classifi cation System (MACS) APPENDIX F: Cerebral palsy publications (to July 2006)

7 INTRODUCTION The Western Australian Cerebral Palsy Register is a population-based data collection that has now been in existence for 26 years. Collection of data for the period commenced in 1977 for the original epidemiological study of cerebral palsy in Western Australia 1-3, and in 1979 additional funding made it possible to continue the data set as an ongoing Register. At that time some changes were made to the data collection and coding which account for some inconsistencies between the data sets before and after 1975 (1975 is included in both). The Register uses multiple sources to ascertain all recognised cases of cerebral palsy born and/or living in Western Australia from 1956 onwards. This report includes only those cases who were born in Western Australia. Information held on the Register is updated when a child reaches the age of 5 years, by which time ascertainment of a birth-year cohort can be considered complete and accurate for inclusion in analyses. There is, therefore, a lag of fi ve years in reporting data, and all information regarding impairments contained in this report relates to fi ndings at the age of 5 years. This report presents Register data in two Sections. Section I: Pre- and Perinatally Acquired Cerebral Palsy covers the years to 1999 in 5- or 10-year groups, from 1960 where Register and denominator data are available for earlier years; otherwise from 1975 or, where data by gestational age or Indigenous status are presented, from The Register collects cases due to postneonatal causes which occur up to the age of 5 years, and this group is presented separately in Section II: Postneonatally Acquired Cerebral Palsy. Mortality data have been reported in a separate publication on the life expectancy of people with cerebral palsy in Western Australia 4. FUNDING The initial data collection was funded in 1977 by NHMRC as part of Professor Fiona Stanley s research fellowship, with additional funds from the King Edward Memorial Hospital Research Foundation and The Australian Neurological Foundation. In 1979 the TVW Telethon Foundation (later called Child Health Research Foundation of Western Australia) funded the Register as an ongoing project and continued this support to mid-1993; the Charles and Sylvia Viertel Research Foundation provided funding during the latter half of From the Register was funded jointly by Healthways and NHMRC and since 1997, solely by NHMRC as part of the Program Grant for Epidemiological Studies in Maternal and Child Health at the Telethon Institute for Child Health Research. We are very grateful for this support.... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER... 5

8 AIMS OF THE WA CEREBRAL PALSY REGISTER The Western Australian Cerebral Palsy Register was set up with the following aims: to monitor trends in the cerebral palsies and identify areas of concern for future investigation, to conduct population-based epidemiological studies of the various cerebral palsy subgroups, particularly to elucidate causes, to evaluate changes in antenatal, obstetric and neonatal care in relation to cerebral palsy as an index of neurological outcome, to identify cerebral palsy as an outcome in other study populations, to aid in the planning of services for individuals with cerebral palsy, and it now aims also to contribute Western Australian data to the Australian Cerebral Palsy Register. THE AUSTRALIAN CEREBRAL PALSY REGISTER The Australian Cerebral Palsy Register (ACPR) commenced in 2002 as a collaborative project between all Australian States and Territories. While only three States - Western Australia, Victoria and South Australia - had established CP Registers at that time, there are now registers operating in every State and Territory. The clearing house is located at the CP Institute in Sydney. A web-based IT system developed for the NSW Cerebral Palsy Register by corporate donors is available to all States and Territories as a means of data collection, management and transfer. Consistency in the classifi cation of cerebral palsy for the ACPR is being addressed by the development of an innovative system of recording clinical features of cerebral palsy using a specially designed form including a training DVD to assist in its introduction and trialling throughout Australia. The ACPR was launched in Sydney by Professor Fiona Stanley during Cerebral Palsy Week in July REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

9 METHODS DEFINITION Cerebral palsy is defi ned by fi ve key elements: (1) it is a group of disorders, (2) it is permanent but not unchanging, (3) it involves a disorder of movement and/or posture and of motor function, (4) it is due to a non-progressive interference/lesion/abnormality, and (5) this interference/lesion/abnormality is in the developing immature brain 5. Despite recent attempts to produce a defi nition suitable to all disciplines 6,7, this defi nition remains the most appropriate for register purposes 8. Cerebral palsy is a description rather than a diagnosis since no information about pathology, aetiology or prognosis can be inferred from it 9. What is to be included in this broad defi nition must therefore be specifi ed. Criteria for the inclusion and exclusion of cases on the Western Australian Register, particularly with regard to syndromes that include a motor impairment, are presented in a paper, What constitutes cerebral palsy? 10. Limits on age of acquisition of cerebral palsy, age of survival, and inclusion of cases with postneonatal causes vary from register to register and must be made clear in order to assess comparability of fi ndings. These criteria, as they relate to the Western Australian Cerebral Palsy Register, are set out below. DATA COLLECTION The Register includes all individuals with cerebral palsy in Western Australia born from 1956 onwards. We include both children who were born here and those who migrate into WA to enable the number of children requiring services to be estimated; the group not born in WA are excluded from birth prevalence analyses. Information is also collected on children with cerebral palsy due to clearly documented postneonatal causes occurring before the age of 5 years. This group is included in prevalence estimates but excluded from studies to investigate other causes of cerebral palsy. Since cases of cerebral palsy due to causes that apparently arise in the neonatal period are likely to be related to the uterine environment, they are classifi ed with the pre- and perinatally acquired group. New cases are ascertained annually from multiple sources (see diagram below), including interstate centres to identify children with cerebral palsy who were born in WA but moved elsewhere before their cerebral palsy was recognised. Data on all cases are updated the year they turn 5, by which time most cases will have come to the attention of the Register, most impairments due to progressive syndromes will have been identifi ed, and impairments that are going to resolve will have done so. In the earlier years of the Register, children with cerebral palsy tended to be referred to one of the metropolitan centres for assessment. More recently there has been a trend to regionalisation of services and the number of data sources has increased considerably with these shifts in service provision.... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER... 7

10 Notifi cation cards (Appendix A) are used to request information on new cases where there is no direct access to medical records, such as regional and interstate centres. Basic demographic, perinatal and diagnostic data are collected on a precoded form shown in Appendix B. The coding manual is available on request. DATA SOURCES Health Department Hospital morbidity data WA Cerebral Palsy Association Rural Paediatric Service State Child Development Centre WA Cerebral Palsy Register Metropolitan and regional hospital physiotherapy depts Preterm birth follow-up studies Disability Services Commission Regional Child Health and Development Centres Private neurologists and paediatricians Interstate paediatricians and CP assessment centres Double-headed arrows indicate an arrangement of reciprocal notifi cation between the Cerebral Palsy Register and (1) the Rural Paediatric Service and (2) preterm birth follow up studies being carried out by neonatologists in Perth. RECORD LINKAGE Cerebral Palsy Register data are computerised using Ingres software as part of the Maternal and Child Health Research Data Base 11 located at the Telethon Institute for Child Health Research. This enables linkage from 1980 onwards with records of all births in Western Australia, thus providing comparison data for the population and a sampling frame for selection of controls. With the appropriate ethics committee approvals, all data sets held on the Maternal and Child Health Research Data Base including data from 1980 onwards can be linked; these include live and stillbirths, deaths, hospital admissions, and the Western Australian Birth Defects Register. Cerebral Palsy Register data are stored electronically in coded form, and names are kept in a separate fi le. DENOMINATORS Denominator data for the years 1956 to 1979 were obtained from Australian Bureau of Statistics annual publications, Demography to , and for 1980 onwards from the Births File on the Maternal and Child Health Research Data Base. It should be noted that population statistics prior to 1967 exclude full-blood Aboriginals. A birth is defi ned as >=20 weeks gestation or >=400 grams birth weight, and a neonatal survivor as an infant who survives beyond the fi rst 28 days of life REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

11 CLASSIFICATION SYSTEM Since the early 1980s the problem of interobserver variation in the classifi cation of cerebral palsy has been addressed by holding regular meetings with doctors and therapists who assess and treat children with cerebral palsy in Western Australia. This group of clinicians designed the cerebral palsy classifi cation form, Description of Motor and Other Disabilities (Appendix C), used in Western Australia until recently. This was based on the Standard Recording of Central Motor Defi cit 14 form developed in the UK in consultation with the international community in the latter half of the 1980s to improve interobserver agreement in classifying cerebral palsy. The WA Register codes cerebral palsy by type and distribution of spasticity: 1 = Right spastic hemiplegia (includes monoplegias) 2 = Left spastic hemiplegia (includes monoplegias) 3 = Spastic diplegia (lower limbs more affected than upper limbs) 4 = Spastic quadriplegia (upper limbs equally or more affected than lower limbs) 5 = Ataxia (coded only if it is the primary cerebral palsy type) 6 = Dyskinesia, mainly athetoid 7 = Dyskinesia, mainly dystonic 8 = Hypotonia These codes are used singly or in combinations of up to three to describe atypical spastic distributions and/or mixed types. However, the predominant type is coded fi rst, and it is this predominant type that is used in the simple analyses by cerebral palsy type shown in this report. Methods of ascertaining type, distribution and severity of cerebral palsy are currently being revised. Up until 2006 the Description of motor and other disabilities form was used to request clinical information from health professionals when this was not available from medical records. Severity codes were loosely defi ned according to function, though it should be noted that in most cases classifi cation of severity was derived from the subjective description recorded in the medical notes. Since 2004 the national ACPR collaboration has been developing a system to standardise the description of cerebral palsy across Australia. This has resulted in a new form, Description of Cerebral Palsy (Appendix D), that is currently being trialled. This form uses validated measurement tools to record spasticity and functional severity of cerebral palsy: the Australian Spasticity Assessment adapted from the Modifi ed Ashworth Scale 15 and shown on reverse side of form, Gross Motor Function Classifi cation System 16 (Appendix E) and Manual Ability Classifi cation System 17 (Appendix F). A similar 5-point scale for speech is currently being developed.... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER... 9

12 CONFIDENTIALITY OF DATA In 1984 the Cerebral Palsy Register Advisory Committee was established in response to an increasing number of requests for access to named data. This Committee controls all matters relating to confi dentiality of Register data. Its 14 members represent all major sources of cases for the Register and also include two parent representatives. Name-identifi ed records are handled according to guidelines set down by the Advisory Committee, the Telethon Institute for Child Health Research, the Health Department of Western Australia and the NHMRC who currently fund our work. Requests for release of named data from outside researchers are referred to the Advisory Committee, and approval must be unanimous. All persons granted access to identifi ed data submit a signed declaration stating their knowledge of confi dentiality requirements and their agreement to adhere to them. Since April 1999, ethics approval has required that consent for registration be obtained before contact can be made with the children or their families. As an ongoing project, The Western Australian Cerebral Palsy Register must seek approval annually from both the Confi dentiality of Health Information Committee of the Health Department of Western Australia and the Princess Margaret Hospital Ethics Committee. ETHICAL CONSIDERATIONS It is not feasible to request the permission of parents or primary care physicians to include children on the Register, primarily because the completeness of the data collection would be compromised. However, we encourage health professionals to inform parents about the Register, and some do this routinely. Efforts are also made to publicise the existence of the Register and to invite feedback from concerned individuals. To date all response has been positive REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

13 CURRENT PROJECTS A major case-control study of cerebral palsy in term and preterm infants born 1980 to 1995 in Western Australia is currently being analysed. This involves approximately 750 cases, about a third of whom were born preterm, 750 controls matched for year of birth, gestational age and plurality and a similar number of intrapartum stillbirths and neonatal deaths. Detailed information was collected regarding family history, mother s medical and obstetric history, the pregnancy, the labour and delivery and the period of hospitalisation after birth with additional data on all cranial imaging and post mortems. New methods of analysing causal pathways are being applied to these data in the hope that new cases can be prevented by identifying points at which a pathway leading to cerebral palsy can be interrupted. Other projects presently being undertaken in Western Australia: Trends in term and preterm cerebral palsy and neonatal mortality over time Mode of delivery in term singleton births resulting in perinatal death or CP Trends in hospitalisations of children with cerebral palsy Postneonatally acquired cerebral palsy in Western Australia The development of a system to achieve reliable descriptions of cerebral palsy, especially spastic cerebral palsy (see Appendix C). INTERNATIONAL DEVELOPMENTS The Western Australian Register is one of the longest-term ongoing cerebral palsy registers in existence and regularly consults with other CP research groups. The enduring spirit of co-operation amongst the cerebral palsy research community worldwide has been further fostered by international meetings to discuss methodological issues and to promote collaboration between centres 18,19, including the recent workshop on Defi nition and Classifi cation of Cerebral Palsy 7. Another result of such meetings was the international multicentre study of cerebral palsy in multiple births which collated data from 11 registers 20. The Surveillance of Cerebral Palsy in Europe (SCPE) is a network of 14 registers in eight European countries which commenced in 2000 with the support of the European Union 5. It covers a population similar to that of the ACPR, and collaborations are anticipated. The growing number of ongoing registers worldwide 21 and the co-operation between registers refl ect the increasing importance attached to cerebral palsy research. This will enable future collaborations to overcome the problems of small numbers within subgroups of cerebral palsy. Ongoing cerebral palsy registers are essential to our ability to scientifi cally address questions about causation which are arising in our courts of law, to effectively counsel parents about risks associated with cerebral palsy and, ultimately, to prevent its occurrence.... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...11

14 RESULTS The following tables and graphs vary with regard to range of birth-year cohorts and type of denominators used depending on availability of population data. While we strongly advocate the use of neonatal survivors as the appropriate denominator for calculating cerebral palsy rates since the rate of neonatal deaths can affect the CP rates, results have often been presented as rates per 1000 live births for two reasons: (1) in order to include data from earlier years when neonatal death data are not available, and (2) in order to present rates that are comparable to other data sets. The highest rates of neonatal deaths, and therefore the largest discrepancies between rates calculated by live births and neonatal survivors, occur in the low gestational age and low birth weight groups, and these are shown for comparison in Tables 3 and 4. OVERALL BIRTH PREVALENCE Figure 1 below shows rates per thousand live births in three-year moving averages. There has been no consistent trend in cerebral palsy birth prevalence rates in Western Australia over the period , but some systematic patterns are discernible. The postneonatally acquired rate appears consistently higher during the 1970s, 1980s and 1990s than it was in the late 1950s and 1960s. Excluding these cases, the CP rate appears to have risen systematically since the early 1970s. Some of this increase is accounted for by an increase in the rate of those with minimal involvement, but there is also an increase in rate of those with greater than minimal involvement from around 1.6/1000 live births in the 1970s to about 2/1000 live births from the mid-80s. Figure 1: Rates per 1000 live births (3-year moving averages) for total CP, CP excluding postneonatal CP (PNN), and CP excluding both postneonatal and minimal CP, Western Australia, Rate per 1000 live births Total CP CP excl PNN CP excl PNN and minimal Year of birth Note: Minimal cerebral palsy was included in the mild category prior to REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

15 Table 1: Cerebral palsy birth prevalence rates per 1000 live births (LB) and per 1000 neonatal survivors (NNS) in Western Australia, Year of birth Live births Neonatal survivors Total CP Rate/1000 LB 95% CI CP excl PNN Rate/1000 NNS Rate/1000 LB 95% CI REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...13

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17 SECTION I: PRE- AND PERINATALLY ACQUIRED CEREBRAL PALSY

18 GENDER OF INFANT Table 2 and Figure 2 show birth prevalence rates for males and females separately. As previously reported, males have been at a consistently higher risk of developing cerebral palsy with an overall ( ) male:female ratio of These rates have been calculated by live births rather than neonatal survivors to enable the inclusion of data back to 1960; however, when calculated by neonatal survivors the difference in rates is almost negligible. Table 2: Cerebral palsy 1 birth prevalence rates per 1000 live births (LB) by gender, Western Australia, in 5-year groups Grouped year of birth GENDER Males (M/F ratio) Females CP 130 (1.8) 72 Rate/1000 LB % CI CP 121 (1.3) 90 Rate/1000 LB % CI CP 105 (1.1) 95 Rate/1000 LB % CI CP 119 (1.4) 84 Rate/1000 LB % CI CP 141 (1.3) 109 Rate/1000 LB % CI CP 160 (1.3) 127 Rate/1000 LB % CI CP 195 (1.5) 131 Rate/1000 LB % CI CP 164 (1.2) 139 Rate/1000 LB % CI Excludes cerebral palsy due to postneonatal causes 2 95% confi dence interval REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...

19 Figure 2: Cerebral palsy* rates by gender in Western Australia, Rate per 1000 live births Males Females BIRTH WEIGHT AND GESTATIONAL AGE Stratifi cation of rates by birth weight in Table 3 and Figure 3a and gestational age in Table 4 and Figure 4a reveal that most of the changes in rates over time have occurred in the lower ranges of birth weight and gestational age. These dramatic rises coincide with the increased survival of very low birth weight and very preterm infants which accompanied the introduction of neonatal intensive care in Western Australia in the fi rst half of the 1970s. As mentioned previously, Tables 3 and 4 show the difference in rates calculated using live births or neonatal survivors as the denominator. This is particularly marked in the lower birth weight and gestational age groups where neonatal survival was lowest and demonstrates the danger of underestimating the magnitude of cerebral palsy risk that can occur when calculating rates by live births. It is also interesting to compare rates analysed by birth weight with those by gestational age. Most studies have reported cerebral palsy rates by birth weight which is more easily and reliably measured in population vital statistics and therefore more widely available, especially in earlier years. However, analysis of data by gestational age makes it possible to separate the effects of poor intrauterine growth from those of preterm birth, which are likely to have quite different causes. In Western Australia good gestational age data for the population are available only from Figure 3a presents rates in commonly reported birth weight groups and shows quite a different picture for birth cohorts after 1980 from Figure 4a which presents rates in commonly reported gestational age groups. It is also important to note the differences produced by presenting data in different ways (Figure 3a compared with 3b and Figure 4a compared with 4b). Birth weight specifi c rates in 3-year moving averages from are shown in Figure 3b (denominators for <1000g group not available before 1975), and gestational age specifi c rates in 3- year moving averages from in Figure 4b.... REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...17

20 Table 3 Birth weight specific cerebral palsy 1 rates per 1000 live births (LB) and per 1000 neonatal survivors (NNS) in Western Australia, in 5-year groups Grouped year of birth Birth weight group <1000g CP Rate/LB % CI Rate/NNS % CI g CP Rate/LB % CI Rate/NNS % CI All <1500g CP Rate/LB % CI Rate/NNS % CI g CP Rate/LB % CI Rate/NNS % CI g CP Rate/LB % CI Rate/NNS % CI All g CP Rate/LB % CI Rate/NNS % CI g CP Rate/LB % CI g CP Rate/LB % CI g CP Rate/LB % CI >=4000g CP Rate/LB % CI All >=2500g CP Rate/LB % CI Rate/NNS % CI Excludes cerebral palsy due to postneonatal causes 2 95 % confi dence interval REPORT OF THE WESTERN AUSTRALIAN CEREBRAL PALSY REGISTER...