Intellectual Disability and Dementia

Research into Practice

Karen Watchman

• Publisher: Jessica Kingsley Publishers
• Year: 2014
• ISBN:
  9780857007964
• Topic: Medicine
• Subtopic: Gerontology Nursing

Presenting the most up-to-date information available about dementia and intellectual disabilities, this book brings together the latest international research and evidence-based practice, and describes clearly the relevance and implications for support and services

Internationally renowned experts from the UK, Ireland, the USA, Canada, Australia and the Netherlands discuss good practice and the way forward in relation to assessment, diagnosis, interventions, staff knowledge and training, care pathways, service design, measuring outcomes and the experiences of individuals, families and carers. The wealth of information offered will inform support and services throughout the whole course of dementia, from diagnosis to end of life. Particular emphasis is placed on how intellectual disability and dementia services can work collaboratively to offer more effective, joined up support.

Practitioners, managers and commissioners will find this to be an informative resource for developing person-centred provision for people with intellectual disabilities and dementia and their families. It will also be a key text for academics and students who wish to be up-to-date with the latest research and practice developments in this field.

PART 1

The Association between Intellectual Disabilities and Dementia

What Do We Know?

1

The Epidemiology of Dementia in
People with Intellectual Disabilities

Amanda Sinai, Trevor Chan, Andre Strydom

The ageing population of people with intellectual disabilities

Significant improvements in health and social care for people with an intellectual disability have led to a dramatic increase in the life expectancy of this population over the past 50 years. The improvements in life expectancy have been particularly striking within the population of people with Down syndrome. It has been estimated that the survival of babies with Down syndrome and congenital birth defects increased from 0 to around 18 years or more in the early 1990s in the USA (Yang et al., 2002) and the number of people with Down syndrome surviving to over 40 years old has been estimated to have doubled in Northern European countries since 1990 (de Graaf et al., 2011). It can therefore be deduced that, at least in the developed world, there is now a much larger proportion of people with intellectual disability living into older adulthood, with associated increased rates of age-related conditions, including dementia. Dementia is now a common factor contributing to death in people with Down syndrome in the UK, and has been found to be a factor in the death in 30 per cent of older people with Down syndrome in Sweden (Englund et al., 2013).

What is dementia?

Dementia is essentially a clinical syndrome which has been defined by various classification systems such as International Classification of Diseases, ICD-10 (World Health Organization, 1993) and the Diagnostic and Statistical Manual of Mental Disorders, DSM-IV (American Psychiatric Association, 2000). Both ICD-10 and DSM-IV require development of a decline in memory and other cognitive functions to make a diagnosis of dementia. ICD-10 requires that symptoms are present for at least six months (World Health Organization, 1993). An updated version of DSM has been published in 2013, called DSM-5 (American Psychiatric Association, 2013). It remains to be seen how the fifth edition of DSM, known as DSM-5, will affect epidemiological research in this field. Diagnostic Criteria for Psychiatric Disorders for Use with Adults with Learning Disabilities (DC-LD) is a diagnostic classification system based on ICD-10, designed for use in adults with moderate to profound intellectual disability (Cooper et al., 2003).

There are several different types of dementia, such as Alzheimer’s disease, vascular, Lewy body and frontotemporal dementias, with different aetiologies and different incidence and prevalence rates. In the general population, Alzheimer’s disease is the most common subtype of dementia, followed by vascular dementia.

Factors affecting population estimates of dementia rates in the population of people with intellectual disabilities

The commonest epidemiological parameters of disorders are prevalence and incidence rates. Prevalence refers to the proportion of a population found to have a condition at a given time. Incidence is the number of new cases of the condition found in a defined population in a given period. Accurate epidemiological estimates of dementia in the intellectual disability population can be influenced by many factors, including diagnostic issues, assessment methods, criteria used, population studied, and type of dementia included. Some of these issues will briefly be considered before a summary of what is known about the epidemiological profile of dementia in the population of people with an intellectual disability.

Diagnostic issues and assessment tools

There are inherent difficulties in assessing for, and diagnosing, dementia in the population of people with an intellectual disability that can affect the estimation of prevalence and incidence rates. First, most adults with an intellectual disability have pre-existing cognitive deficits, including loss of short-term memory, and it can be quite difficult to establish a decline in cognition or function, particularly in those with limited speech abilities and low functional abilities. Second, most of the neuropsychological screening and assessment tools used in the general population are not suitable for adults with an intellectual disability. Although there are some tools that have been specifically developed for use in the population of people with intellectual disabilities, there are no established assessment batteries with satisfactory psychometric properties that can be used across the ability spectrum. Clinicians may therefore need to rely on informants’ report of symptoms (Jamieson-Craig et al., 2010), which may not always be accurate.

The diagnostic stability of dementia diagnoses in those with an intellectual disability, who did not have Down syndrome, has been explored by Strydom et al. (2013a). They established that diagnostic instability may be more common in the intellectual disability population due to additional challenges in diagnosing dementia. These additional challenges may include variable quality of informant reports, difficulties in the assessment of those with moderate and severe intellectual disability or sensory impairments, difficulties in detecting protracted periods of plateau in vascular dementia and the ‘floor effect’ in advanced dementia in the absence of longitudinal information.

Definitions of dementia used

As a result of the differences between criteria, estimates of population rates may vary according to the definition of dementia used. For example, the ICD-10 criteria often result in a more restrictive diagnosis and subsequent lower estimates of population rates. Estimates may also vary according to which subtypes of dementia are included; many epidemiological surveys tend to focus on Alzheimer’s disease, and may miss cases of other dementias such as frontotemporal dementia, as these have a different presentation and age of onset. Study designs therefore require specific consideration to ensure inclusion of rarer types of dementia.

It is well established that there are much higher rates of Alzheimer’s disease in people with Down syndrome as compared to the general population, and compared to other people with an intellectual disability. It is therefore important to be clear about whether adults with Down syndrome are included or excluded from epidemiological studies of dementia in those with an intellectual disability, and it is easier to interpret rates if those with Down syndrome and those without Down syndrome are reported separately.

The age thresholds used in epidemiological studies of dementia may also affect prevalence and incidence estimates. Dementia often occurs at a younger age than expected, particularly in people with Down syndrome, and rates may be underestimated if relevant age groups are excluded. Finally, living arrangements may also be important, as those living in institutions, which remain prevalent in some parts of the world, may differ in many ways from community-dwelling older adults with an intellectual disability, which could affect their likelihood of survival and of subsequently developing dementia.

The impact of these issues upon dementia estimates in the intellectual disability population can be demonstrated by the available literature. In a postal survey of known dementia cases amongst adults using intellectual disability services in New York State, USA, Janicki and Dalton (2000) found an overall prevalence rate of 6.1 per cent in those aged 60 and older. This figure was comparable to that in the general population, although rates were much higher in the Down syndrome population than in those who did not have Down syndrome. However, the survey may have underestimated dementia rates as it relied upon identification of those with known diagnoses, rather than screening for unidentified cases. In contrast, Shooshtari et al. (2011) used data from administrative provincial databases in Canada and a matched case-control design, and found a prevalence for dementia of 13.8 per cent for adults with intellectual disabilities aged 55 and older when compared to the matched comparison group.

Prevalence of dementia in people with intellectual disabilities

Dementia prevalence in people with Down syndrome

A number of studies have confirmed that dementia is common in older adults with Down syndrome, and that the prevalence increases sharply between ages 40 and 60. In a large study of people with Down syndrome aged 45 years and older in the Netherlands, it was found that up to the age of 60 the prevalence of dementia doubled with each five-year interval up to the age of 49 – the prevalence was 8.9 per cent. Between the ages of 50 and 54, it was 17.7 per cent and between 55 and 59, it was estimated at 32.1 per cent (Coppus et al., 2006). A study in the UK found that prevalence rates using CAMDEX (Cambridge Mental Disorders of the Elderly Examination) criteria for Alzheimer’s disease increased from 3.4 per cent, to 10.3 per cent, to 40 per cent among 30–39, 40–49 and 50–59 age groups, respectively (Holland et al., 1998). An Irish study, using modified DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) criteria, found age-specific prevalence rates of 1.4 per cent for those under age 40, 5.7 per cent for those aged 40–49 and 30.4 per cent for those aged 50–59 (Tyrrell et al., 2001).

Studies have varied in their estimates of prevalence of dementia beyond the age of 60. Tyrrell et al. (2001) have described a rate of 41.7 per cent among those aged 60 and over, and 50 per cent among those aged 70 or older. One study from the Netherlands, based on an institut...

Table of contents

• Cover
• Of Related Interest
• Title Page
• Copyright
• Contents
• Figures
• Tables
• Foreword
• Introduction
• Part 1 The Association between Intellectual Disabilities and Dementia: What Do We Know?
• Part 2 Experiences of Dementia in People with Intellectual Disabilities: How Do We Know?
• Part 3 Service Planning: What Are We Going to Do?
• List Of Contributors
• Subject Index
• Author Index
• Also available