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Centre for Disability Research, Division of Health Research, Lancaster University, LA1 4YT, United KingdomCentre for Disability Research and Policy, University of Sydney, Australia
Review of 48 studies on prevalence in people with intellectual disabilities.
•
Pooled estimate 22.2% (95% CI 19.6–25.1) for general samples.
•
Prevalence increased with increasing level of intellectual disability.
•
Pooled estimate 12.4% (95% CI 9.1–16.7) for people with Down syndrome.
•
Prevalence increased with age in people with Down syndrome.
Abstract
Purpose
Epilepsy is more common in people with intellectual disabilities than in the general population. However, reported prevalence rates vary widely between studies. This systematic review aimed to provide a summary of prevalence studies and estimates of prevalence based on meta-analyses.
Method
Studies were identified via electronic searches using Medline, Cinahl and PsycINFO and cross-citations. Information extracted from studies was tabulated. Prevalence rate estimates were pooled using random effects meta-analyses and subgroup analyses were conducted.
Results
A total of 48 studies were included in the tabulation and 46 studies were included in meta-analyses. In general samples of people with intellectual disabilities, the pooled estimate from 38 studies was 22.2% (95% CI 19.6–25.1). Prevalence increased with increasing level of intellectual disability. For samples of people with Down syndrome, the pooled estimate from data in 13 studies was 12.4% (95% CI 9.1–16.7), decreasing to 10.3% (95% CI 8.4–12.6) following removal of two studies focusing on older people. Prevalence increased with age in people with Down syndrome and was particularly prevalent in those with Alzheimer's/dementia.
Conclusion
Epilepsy is highly prevalent in people with intellectual disabilities. Services must be equipped with the skills and information needed to manage this condition.
Intellectual disability (often referred to as ‘learning disabilities’ in the United Kingdom) refers to a significant general impairment in intellectual functioning that is acquired during childhood, typically operationalised as scoring more than two standard deviations below the population mean on a test of general intelligence [
]. While estimates of the prevalence of intellectual disability vary widely, it has been estimated that approximately 2% of the adult population have intellectual disability [
]. In people with intellectual disabilities, estimates of the prevalence of epilepsy vary due to differences in the methods used and inherent population biases [
] to 30.7% in a random sample of 753 people with intellectual disabilities aged 40 or more from Ireland's National Intellectual Disability Database (NIDD) [
]. In a systematic review of the prevalence of chronic health conditions in children with intellectual disabilities, the most common condition was epilepsy [
] with prevalence rates in the 14 studies identified ranging from 5.5% to 35.0%, with an overall weighted mean prevalence rate of 22.0% (95% CI 20.8–23.2).
Despite variation in reported prevalence figures, it is clear that the prevalence of epilepsy in people with intellectual disabilities is much greater than in the general population. Further, for people with intellectual disabilities and epilepsy, co-morbidities may be common. Over half of a representative sample of children with intellectual disability and active epilepsy were reported to have a psychiatric diagnosis [
]. However, conflicting findings exist and there is no consensus as to whether people with both intellectual disability and epilepsy are at increased risk of psychiatric morbidity compared to their peers with either epilepsy or intellectual disability alone [
]. Such wide differences highlight the need to examine prevalence rates taking into account factors such as the degree of intellectual disability of the sample. Samples based on, for example, those in contact with intellectual disability services are likely to miss out some people with less severe intellectual disabilities. A further issue is that the ascertainment of epilepsy is not consistent across studies, both in terms of the definition of epilepsy used, and how the information is collected.
The aim of this review is to summarise existing research on the prevalence of epilepsy in people with intellectual disabilities, including studies relating specifically to people with Down syndrome which is the most common genetic cause of intellectual disabilities [
]. The review also aims to provide pooled prevalence estimates for studies taking into account factors such as age and level of intellectual disability. Whilst existing reviews have considered the prevalence of epilepsy in people with intellectual disabilities, these reviews do not cover more recent studies on prevalence that now provide more data, particularly in relation to adults with intellectual disabilities. As highlighted in one earlier review, adults have previously been underrepresented in research on the epidemiology of epilepsy in people with intellectual disabilities, with the vast majority of published data pertaining to children [
]. As this review aims to estimate epilepsy prevalence in the general population of people with intellectual disabilities or Down syndrome, it does not include studies relating to less common specific genetic conditions associated with intellectual disabilities, although it is evident that work on such conditions has been published [
Electronic literature database searches were conducted in Medline, Cinahl and PsycINFO on EBSCO. In addition, the reference lists of articles meeting the inclusion criteria were searched. The reference lists of key book chapters were also searched [
in: Taggart L. Cousins W. Health promotion for people with intellectual and developmental disabilities. McGraw Hill (Open University Press),
Maidenhead2014: 77-87
]. Searches were completed on 19 June 2014. Searches included terms relating to both prevalence and mortality to create a pool of articles on prevalence or mortality, with articles on mortality being retained for a separate review. Searches combined terms for epilepsy, intellectual disabilities, and prevalence/mortality with the Boolean operator ‘and’. Full details of the search terms are given in Appendix A.
2.1 Inclusion criteria
•
Peer reviewed
•
English Language full text
•
Published from 1990
•
Primary research
•
Present exact figures on the prevalence of epilepsy
•
Samples where 50% or more have intellectual disabilities or mixed samples where results are disaggregated for people with intellectual disabilities
•
Studies using representative samples of people with intellectual disabilities or samples representative of specific sub-groups of people with intellectual disabilities (e.g. specific level of intellectual disability, specific age band)
2.2 Exclusion criteria
•
Case studies
•
Case series
•
Reviews
•
Studies based on neonates (new born infants up to 28 days after birth)
•
Studies on conditions where intellectual disabilities cannot be assumed (e.g. cerebral palsy) where results not disaggregated for people with intellectual disabilities
•
Studies on specific syndromes associated with intellectual disabilities with the exception of Down syndrome
•
Studies where ascertainment of epilepsy could be confounded with febrile seizures
•
Studies employing samples unrepresentative of specific sub-groups of people with intellectual disability e.g. only those attending for inpatient specialist medical care
•
Studies not presenting exact figures
Initially, titles and abstracts were used to exclude those studies which were obviously not within the scope of reviews on prevalence or mortality. Those retained for further screening were those for which relevance could not be assessed without accessing full text, or those that were chosen as potentially within scope. These studies were screened by the first and second author and discussed until consensus was reached on whether or not they met the inclusion criteria. Those relevant to other future planned reviews (e.g. mortality) were filed for future reference.
Where multiple articles used the same sample or samples were likely to have considerable overlap, only the most recent study was included. One exception was a study based on adults with intellectual disabilities registered with the Leicestershire Intellectual Disability Register for the period 1993–2010 which reported a prevalence of 19.1% in a sample of 5391 [
]. As this study focuses on sudden and unexpected death in epilepsy (SUDEP), it does not outline the methodology for obtaining this estimate. As such, it was decided to include an earlier study based on the same register which focused on epilepsy prevalence [
]. A further study including only people with Down syndrome which was partly based on the Leicestershire Intellectual Disability Register was also included [
Information from the included studies was extracted by the first author and this information was tabulated (see Table 1).
Table 1Summary of included studies giving prevalence rates for epilepsy in people with intellectual disabilities. Figures under male, and levels of ID columns relate to characteristics of the study sample. Sorted by author name. Studies only looking at Down syndrome listed separately at end of table.
An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.
Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.
A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.
Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.
A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
Calculated from available figures not reported directly.
Abbreviations: ns, not stated; SZ, seizures; ILAE, International League Against Epilepsy; AED, anti-epileptic drug; DS, Down syndrome; ID, intellectual disabilities; LD, learning disabilities; CLDT, community learning disability team; MH, ‘mental handicap’; SPID, Severe or profound intellectual disabilities; LS, living situation; CP, cerebral palsy; BPSMR, Board for Provision of Services to the Mentally Retarded; MCA, multiple congenital anomalies; AE, acquired encephalopathy; FXS, Fragile X syndrome; CNS, central nervous system; TQQ, the ‘Ten Questions’ Questionnaire; OR, odds ratio; RS, Rett syndrome.
a Calculated from available figures not reported directly.
b Presented as Total score (epilepsy definition score/ascertainment of epilepsy score/subgroup analysis score).
c ←, included in previous figure; →, included in next figure.
d entry age includes those without ID in main study
]. A method for evaluating aspects of quality considered important in relation to obtaining valid estimates of the prevalence of epilepsy was developed. The selected quality indicators were:
1.
Definition of epilepsy:
•
Score 2: Definition given (e.g. ILAE)
•
Score 1: Partial definition given – some information (e.g. database codes used, epilepsy diagnosis) but incomplete
•
Score 0: Not stated (no criteria for epilepsy given)
2.
Ascertainment of epilepsy – this refers to the identification of those in the sample with epilepsy and not any subsequent follow up of those identified as having possible epilepsy. The following scores were allocated:
•
Score 1: Questionnaire self-completion by informant
•
Score 2: Interview with informant
•
Score 3: Extracted from records or databases
•
Score 4: Clinical examination
If multiple methods were used, the highest level was entered as the score.
3.
Prevalence figures presented for subgroup(s). A score of 1 was allocated for each of the following subgroups for which prevalence figures were reported.
•
Age
•
Gender
•
Level of intellectual disability
•
Other – prevalence for other subgroup(s) given (e.g. those with dementia)
A score was awarded if the information was presented in a bar chart, or in an alternative format such as relative risk. Scores could range from 0 to 4. Studies were not excluded based on quality scores and scores are presented in the first column of Table 1.
2.4 Meta-analysis
For each study, the sample size and number of cases of epilepsy in the sample were entered as effect size data in Comprehensive Meta-Analysis Version 2.2 software (www.Meta-Analysis.com). Prevalence estimates were pooled using random effects meta-analysis. For the main random effects pooled estimates, heterogeneity between studies was summarised using I2 and Q statistics. Subgroup analyses were conducted using between study moderator variables and within study subgroups. To compare across subgroups, the Q-test was used. Statistical significance was set at p value < .05.
3. Results
The process of identifying studies for inclusion is summarised in Appendix B. Electronic database searches identified a total of 1332 references, with 1099 remaining after removal of duplicates. Following the first examination of studies, 144 remained in a pool of articles relating to prevalence or mortality. After examination of full text articles from this pool and the addition of articles cited within these, 48 articles met the criteria for inclusion in relation to the prevalence of epilepsy and these are summarised in Table 1. Studies only including people with Down syndrome are presented separately at the end of Table 1.
3.1 Geographical spread
The majority of studies (42) were from high income countries, with just six studies from Low and Middle Income countries. The studies included a wide range of countries, with the greatest number for one country being seven studies from the United States [
Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.
A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.
Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
Studies were almost entirely cross-sectional and based on retrospective review of records, questions completed either by self-report or interview, or clinical examination. There were three prospective cohort studies [
] although in the latter authors only present prevalence rates for the last data collection round. In one retrospective study people could be included in more than one age-band estimate as there was an average of 12 years of follow-up for those with disabilities [
Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
]. For prospective or retrospective cohort studies where people could be included in prevalence estimates at more than one time point, only the most recent data collection point was included. Analyses looked at subgroups using between study moderator variables, and also within study subgroups.
3.3.1 General samples versus samples of people with Down syndrome
An a priori decision was taken to compare studies based solely on samples of people with Down syndrome to general samples of people with intellectual disabilities. This was done in view of evidence suggesting that the prevalence of epilepsy is lower in people with Down syndrome than in general samples of people with intellectual disabilities (although these general sample figures are likely to include a number of people with Down syndrome). Whether or not studies included only people with Down syndrome was used as a between study moderator variable (see Table 2). The pooled estimate for 38 studies of general samples of people with intellectual disabilities was 22.2% (95% CI 19.6–25.1). There was significant heterogeneity between the studies (I2 = 96.4%, Q = 1025.2, df = 37, p < .001). The pooled estimate for studies including only people with Down syndrome was 13.6% (95% CI 9.9–18.4). There was significant heterogeneity between studies (I2 = 91.7%, Q = 84.3, df = 7, p < .001). Fig. 1 presents a forest plot of the 38 studies based on general samples and the 8 studies based on samples of people with Down syndrome only.
Table 2Random effects meta-analysis pooled estimates of prevalence of epilepsy.
For studies using general samples of people with intellectual disabilities, level of intellectual disability was used as a between study moderator variable (see Table 2). This classified studies as: ‘All’ (study representative of all levels of intellectual disability); ‘Less’ (study representative of those with less severe intellectual disabilities e.g. excludes those with severe/profound intellectual disability); ‘More’ (study representative of those with more severe intellectual disabilities e.g. excludes those with mild intellectual disability). The pooled estimate for studies including all levels of intellectual disability was 22.2% (95% CI 19.6–25.0), whereas the estimate for studies classed as ‘less severe’ was 7.3% (95% CI 4.5–11.6) and the estimate for ‘more severe’ 41.6% (95% CI 32.1–51.8). In view of the effect of level of intellectual disability on pooled prevalence estimates, subsequent analyses only included those 29 studies which included all levels of intellectual disability.
3.3.3 Age group
Broad age group was used as a between study moderator variable for the 29 studies which included all levels of intellectual disability and which were not restricted to people with Down syndrome. Age group was classed as adult, child, or mixed (adult and child). This was based on the main age group of the study sample, so for example a study would be classed as ‘adult’ if it included mainly adults and a small number of 16 year olds, and a study would be classed as ‘child’ if it included mainly children and a small number of 20 year olds. Estimates for these broad age groups did not differ significantly (see Table 2).
3.3.4 Country economy
Country economy (High or Low and Middle Income (LAMI)) was also used as a between study moderator variable for the 29 studies which included all levels of intellectual disability and which were not restricted to people with Down syndrome. Countries in which studies were undertaken were classed as ‘high income’ or ‘low and middle income’ based on the World Bank list of economies [
]. This classifies countries according to 2013 gross national income (GNI) per capita: low income, $1045 or less; lower middle income, $1046–4125; upper middle income, $4126–12,745; and high income, $12,746 or more. Taiwan (not included in country classification) was classed as High Income. One study included 14 European countries of which one was upper middle income and this study overall was classed as ‘high income’ [
]. There was no significant difference in the pooled estimates (see Table 2).
3.4 Within study subgroup analyses
Further meta-analyses were then conducted which included information on prevalence from within study subgroups, for example where studies presented prevalence rates separately by level of intellectual disability, gender or age bands. Studies which only included a relevant subgroup (e.g. a sample including only people with mild intellectual disability) were also included in these analyses.
3.4.1 Level of intellectual disability
For level of intellectual disability, firstly prevalence rates were included for those with mild intellectual disability and the combined prevalence for those with moderate, severe or profound intellectual disability. Combining moderate, severe and profound intellectual disability was done to maximise the number of studies that could be included as few studies presented results for each of these three levels of intellectual disability separately. The pooled estimate for moderate/severe/profound intellectual disability from 14 studies was 30.4% (95% CI 25.5–35.7) compared to 9.8% (95% CI 7.6–12.4) from 13 studies for those with mild intellectual disability (see Fig. 2).
Fig. 2Forest plot for prevalence mild versus moderate/severe/profound intellectual disability.
Pooled estimates were also calculated for the studies which did provide separate estimates for any of the moderate, severe or profound categories. For moderate intellectual disability, the pooled estimate was 16.7% (95% CI 10.8–25.0), compared to 27.0% (95% CI 16.1–41.5) for severe intellectual disability and 50.9% (95% CI 36.1–65.5) for profound intellectual disability.
3.4.2 Gender
Where male and female prevalence figures were given separately, pooled estimates were male 24.8% (95% CI 19.6–30.8) and female 22.2% (17.3–28.1). One study in the male/female subgroup analysis only included those with mild or moderate intellectual disability but was nonetheless included in the analysis [
Studies presenting results separately for age bands were considered using age band as a subgroup within study. Studies presenting results for only one age band were also included in this analysis. The broad age bands used were 0–18, 19–49, and 50+. However, a 5 year leeway was given for these age bands at both the upper and lower limit so, for example, a figure for those aged 19–54 or 17–54 would be included in the 19–49 category. Age bands from McDermott et al. [
] were not included as due to participants having an average of 12 years of follow-up time a person could be in more than one age band and they were thus not independent subgroups. Figures for a specific age (e.g. age 22) were included in the appropriate age band. Overall, there was not a significant difference by age band although the prevalence for age band 19–49 (26.0% (95% CI 21.2–31.5)) was slightly higher than that for the 0–18 age band (21.6% (95% CI 17.9–25.9) and the 50+ age group (21.5% (95% CI 17.0–26.9).
3.5 Down syndrome
Eight studies focussed exclusively on people with Down syndrome [
]. A further eight studies included some results disaggregated for people with Down syndrome in the overall sample. Results from meta-analyses in relation to people with Down syndrome are given in Table 3. In these analyses, prevalence rates from studies looking only at people with Down syndrome were combined with prevalence rates given in other studies which presented results for people with Down syndrome as a within study subgroup (excluding studies which did not include all levels of intellectual disability). No rates disaggregated by gender were identified.
Table 3Meta-analysis estimates for people with Down syndrome.
Firstly, pooled prevalence for people with Down syndrome was estimated by combining the prevalence rates from studies looking only at people with Down syndrome with prevalence rates for people with Down syndrome presented as a within study subgroup (excluding studies which did not include all levels of intellectual disability). The pooled estimate was 12.4% (95% CI 9.1–16.7). There was significant heterogeneity between studies, I2 = 87.4%, Q = 95.3, df = 12, p < .001.
Pooled prevalence was also estimated for age bands. This showed a significant effect of age band, with the pooled estimate rising from 6.9% (95% CI 3.8–12.0) at age 0–18, to 9.0% (95% CI 5.9–13.5) at age 19–49, and 26.0% (95% CI 16.1–39.2) at age 50+.
In view of the increased rate of epilepsy in older people with Down syndrome, overall prevalence was then estimated excluding two studies which looked at samples of people with Down syndrome aged 35+ only [
]. Based on data from 11 studies, the pooled estimate was 10.3% (95% CI 8.4–12.6), I2 = 57.0%, Q = 23.2, df = 10, p < .01. However, it should be noted that these studies did not include all age bands, with some including only adults and other including only children.
Finally, a small number of studies presented prevalence rates separately for those with and without Alzheimer's disease/dementia. The pooled prevalence for those with Alzheimer's/dementia was 53.3% (95% CI 41.9–64.4) compared to 12.8% (95% CI 7.7–20.4) for those specifically noted not to have Alzheimer's/dementia. It is not possible to give the mean age for those with and without Alzheimer's disease/dementia overall. However, the mean age for both groups is available in two studies: 54.7 (SD 7.5) for those with Alzheimer's disease/dementia compared to 45.6 (SD 7.3) for those without [
] and one study (controlling for age, gender and level of understanding) found associations with epilepsy and some psychological and behaviour problems [
]. However, other studies found that people with intellectual disability and epilepsy were not more likely to have co-morbid psychiatric and/or behavioural problems than those with intellectual disabilities without epilepsy. Reported findings include: being significantly less likely to have behavioural disturbances (17.6% vs 27.9%) [
A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
]; no association between epilepsy and mental health concerns, with 46.7% of those with epilepsy reporting mental health problems compared with 48.1% of those without epilepsy [
People with intellectual disabilities and epilepsy were found to have more associated impairments (2.7) than those without epilepsy (1.2) and were more likely to have: speech handicap (73.6% versus 50.0%), motor handicap (54.4% versus 14.4%), and blindness (14.2% versus 1.4%) [
]. After adjusting for age, gender and level of understanding, those with epilepsy were more likely to have: a range of physical disabilities (adjusted OR 1.8, 95% CI 1.5–2.2); problems with wetting (OR 2.7, 95% CI 2.1–3.4), soiling (OR 2.2, 95% CI 1.6–3.1) and walking (OR 2.5, 95% CI 2.0–3.2) [
]. Those with intellectual disability were also found to be more likely to have joint disease (29.3% versus 16.8% for those with intellectual disability without epilepsy, adjusted OR 2.1, 95% CI 1.5–3.1), gastrointestinal disease (34.5% versus 23.4%, adjusted OR 1.8, 95% CI 1.3–2.5), and stroke (5.2% versus 1.9%, adjusted OR 3.3, 95% CI 1.4–9.0) [
Despite the variation in reported prevalence rates between studies, it is clear that the prevalence of epilepsy is high in people with intellectual disabilities worldwide. The results suggest that in general samples of people with intellectual disabilities, approximately one in five people will have epilepsy, with the pooled estimate from 38 studies being 22.2% (95% CI 19.6–25.1). For samples of people with Down syndrome excluding two studies focusing on older people, the rate is lower with approximately one in ten people having epilepsy, with the pooled estimate from data in 11 studies being 10.3% (95% CI 8.4–12.6). In studies where this information was available, those with intellectual disabilities and epilepsy had more physical impairments than those without epilepsy. However, whilst psychiatric or behavioural co-morbidity was common, rates were not necessarily higher than in those with intellectual disabilities without epilepsy. A review specifically addressing co-morbidity in people with intellectual disabilities and epilepsy extending beyond studies that present figures on prevalence (e.g. [
The prevalence of epilepsy is related to level of intellectual disability. In 29 studies which included all levels of intellectual disability, the pooled estimate was 22.2% (95% CI 19.6–25.0), whilst for four studies with samples skewed towards less severe intellectual disability the pooled estimate was 7.3% (95% CI 4.5–11.6) and for five studies skewed towards more severe intellectual disability the pooled estimate was 41.6% (95% CI 32.1–51.8). Similarly, data from 13 studies gives a pooled estimate for those with mild intellectual disability of 9.8% (95% CI 7.6–12.5) compared to 30.4% (95% CI 25.5–35.7) for those with moderate, severe or profound intellectual disability. Few studies give figures separately for those with moderate, severe or profound intellectual disability but it is clear that prevalence increases with level of intellectual disability. The pooled estimate for moderate intellectual disability from five studies was 16.7% (95% CI 10.8–25.0), for severe intellectual disability from three studies 27.0% (95% CI 16.1–41.5) and for profound intellectual disability from four studies 50.9% (95% CI 36.1–65.5).
Age was not found to be a significant factor for general samples of people with intellectual disabilities, although the rate for those aged 19–49 was slightly higher at 26.0% (95% CI 21.2–31.5) than for 0–18 year olds (21.6%, 95% CI 17.9–25.9) and 50+ year olds (21.5%, 95% CI 17.0–26.9). However, for people with Down syndrome there was a clear increase in prevalence with age. Data from two studies for those aged 0–18 gave a pooled estimate of 6.9% (95% CI 3.8–12.0), compared to 9.0% (95% CI 5.9–13.5) for three studies giving data for 19–49 year olds and 26.0% (95% CI 16.1–39.2) for three studies giving data for those aged 50 or more. An increase with age was also found for people with Down syndrome in a study by van Schrojenstein Lantman-de Valk et al. [
], with the rates being 4.9% at age 0–19, rising to 36.4% for those age 60 or more. However, it was not possible to include these figures in the meta-analysis as sample sizes for individual age bands were not identified. Similarly, an increasing prevalence of epilepsy with age was found for a small sample of people with Down syndrome [
] but these figures could not be included in the meta-analysis due to participants being included in more than one age band estimate depending on the number of years the person was followed up for.
Overall, it is clear that for people with Down syndrome, epilepsy prevalence increases with age. This increase is likely to be mainly accounted for by the increasing presence of Alzheimer's disease/dementia in people with Down syndrome as they age. The pooled estimate for those with Alzheimer's disease/dementia from four studies was 53.3% (95% CI 41.9–64.4) compared to 12.8% (95% CI 7.7–20.4) for two studies explicitly giving data for those without Alzheimer's/dementia. Further, in one study, epilepsy was found here to be significantly more common in persons at end-stage (84.0%) versus persons at mid-stage Alzheimer's disease (39.4%) [
There are a number of limitations to this review. Whilst studies were identified from a large range of countries, the review is restricted to English language publications. All data was extracted by one reviewer and extraction of data by two reviewers independently would have reduced the possibility of errors. In some instances it was necessary to calculate figures from reported data as they were not reported explicitly (e.g. obtaining the number of epilepsy cases from the overall sample number and reported prevalence rate or vice versa) and two minor discrepancies arose. Firstly, calculating figures from McVicker et al. [
] on prevalence by age band resulted in a total number of epilepsy cases of 19 compared to a reported number of 18. Secondly, calculating figures from Wong [
Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
]. However, many of the studies identified did not present a definition of epilepsy, generally referring to either a diagnosis of epilepsy or the presence of epilepsy. The lack of detail given regarding the definition of epilepsy in many studies means that it is not possible to determine whether reported prevalence rates related to active epilepsy or lifetime epilepsy. The issue of defining epilepsy is not straightforward [
]. Where definitions were provided, these included standard definitions based on International League Against Epilepsy (ILAE) criteria and other definitions specifying variable criteria in relation to number of seizures, anti-epileptic drug (AED) use and time spans. In addition, the source of information used to ascertain epilepsy is variable between studies which may lead to varying levels of accuracy in obtained rates.
In addition to the variation in prevalence rates that is likely to be due to differences in the definition of epilepsy used and the source of data in studies, there is also likely to be an unknown number of cases where epilepsy has been misdiagnosed due to the misinterpretation of behavioural, physiological, syndrome related, medication related or psychological events by parents, paid carers and health professionals [
Finally, the review has focussed on prevalence in the general population of people with intellectual disabilities or Down syndrome and has not included studies on less common syndromes such as Fragile X syndrome. Future review work could consider prevalence in a greater range of specific syndromes associated with intellectual disabilities.
5. Conclusion
This review aims to provide an up to date summary of research on the prevalence of epilepsy in people with intellectual disabilities. The pooling of estimates from studies, and the examination of factors which account for some of the heterogeneity of reported prevalence rates between studies, allows for the provision of more robust figures on prevalence. With around one in five people with intellectual disabilities having epilepsy, it is important that services are equipped with the information and skills needed to manage epilepsy in this population. A recent report provides information on reasonable adjustments that can be made to improve epilepsy care for people with intellectual disabilities [
] The ideas, information and examples of good practice in relation to reasonable adjustments provided within this report should help services improve provision for this highly prevalent condition.
Conflict of interest statement
There is no conflict of interest.
Acknowledgements
This work was supported by Public Health England. However, the findings and views reported in this paper are those of the authors and should not be attributed to Public Health England. We would like to thank Howard Ring for comments on the draft of this manuscript.
Appendix A. Electronic search strategy
Tabled
1
MEDLINE AND CINAHL
Limits: 1990; English; Human
(TI (learning N1 (disab* or difficult* or handicap*)) OR TI (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR TI (intellectual* N1 (disab* or impair* or handicap*)) OR TI development* N1 disab* OR TI (multipl* N1 (handicap* or disab*)) OR TI “Down* syndrome” OR (MH “Developmental Disabilities/EP/MO”) OR (MH “Intellectual Disability+/EP/MO”) OR (MH “mentally disabled persons”)) OR (AB (learning N1 (disab* or difficult* or handicap*)) OR AB (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR AB (intellectual* N1 (disab* or impair* or handicap*)) OR AB development* N1 disab* OR AB (multipl* N1 (handicap* or disab*)) OR AB“Down* syndrome”)
AND
(MH “Epilepsy+/MO/EP”) OR (TI epilep* OR TI seizure* OR TI convulsi* OR AB epilep* OR AB seizure* OR AB convulsi*)
AND
(TI incidence OR TI prevalence OR TI mortality OR TI death OR AB incidence OR AB prevalence OR AB mortality OR AB death) OR (MH “Incidence”) OR (MH “Prevalence”) OR (MH “Mortality+”)
DE “Epilepsy” OR DE “Epileptic Seizures” OR (DE “Seizures” OR DE “Audiogenic Seizures” OR DE “Epileptic Seizures” OR DE “Grand Mal Seizures” OR DE “Petit Mal Seizures” OR DE “Status Epilepticus”) OR (TI epilep* OR TI seizure* OR TI convulsi* OR AB epilep* OR AB seizure* OR AB convulsi*)
AND
(TI incidence OR TI prevalence OR TI mortality OR TI death OR AB incidence OR AB prevalence OR AB mortality OR AB death) OR DE “Epidemiology” OR DE “death and dying” OR DE “mortality rate”
AND
DE “Intellectual Development Disorder” OR DE “mental retardation” OR DE “developmental disabilities” OR (TI (learning N1 (disab* or difficult* or handicap*)) OR TI (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR TI (intellectual* N1 (disab* or impair* or handicap*)) OR TI development* N1 disab* OR TI (multipl* N1 (handicap* or disab*)) OR TI “Down* syndrome”) OR AB (mental* N1 (retard* or disab* or deficien* or handicap* or disorder*)) OR AB (intellectual* N1 (disab* or impair* or handicap*)) OR AB development* N1 disab* OR AB (multipl* N1 (handicap* or disab*)) OR AB “Down* syndrome”
in: Taggart L. Cousins W. Health promotion for people with intellectual and developmental disabilities. McGraw Hill (Open University Press),
Maidenhead2014: 77-87
Concurrent medical conditions and health care use and needs among children with learning and behavioral developmental disabilities. National Health Interview Survey, 2006–2010.
An audit of adults with profound and multiple learning disabilities within a West Midlands Community Health Trust – implications for service development.
A general practice-based prevalence study of epilepsy among adults with intellectual disabilities and of its association with psychiatric disorder, behaviour disturbance and carer stress.
Developmental level and other factors associated with symptoms of mental disorders and problem behaviour in adults with intellectual disabilities living in the community.
Adults with intellectual disabilities living in Hong Kong's residential care facilities: a descriptive analysis of health and disease patterns by sex, age, and presence of Down syndrome.
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