Review articleAnxiety disorders in children and adolescents with intellectual disability: Prevalence and assessment
Introduction
The mental health of individuals with intellectual disability (ID) has received growing attention over recent years. Little more than forty years ago, it was widely presumed that individuals with ID could not experience mental health problems (Matson, Belva, Hattier, & Matson, 2012), however the elevated rates of mental health problems among individuals with ID is now well established (Dekker et al., 2002c, Einfeld and Tonge, 1996, Totsika et al., 2011). Although reported prevalence rates vary, population studies of children and adolescents with ID have repeatedly identified rates of comorbid mental health problems at 30–40% (Einfeld and Tonge, 1996, Linna et al., 1999, Rutter et al., 1970, Totsika et al., 2011). Relatively fewer studies have incorporated full psychiatric assessments (thus enabling diagnoses of mental health disorders), however, it is noteworthy that three studies that did, conducted in the UK, the Netherlands and Norway, report strikingly similar rates (36–39%) of DSM/ICD mental health disorders among children and adolescents with ID (Dekker and Koot, 2003, Emerson and Hatton, 2007, Stromme and Diseth, 2000). These figures are markedly higher than corresponding estimates of 8–17% in typically developing populations of young people (Costello et al., 2003, Emerson and Hatton, 2007, Merikangas et al., 2010, Roberts et al., 2007).
With a larger literature base surrounding the mental health of typically developing children and adolescents, prevalence rates of specific mental health disorders are now better established, and anxiety disorders consistently emerge near the top of the list (Costello et al., 2003, Emerson and Hatton, 2007, Roberts et al., 2007). In contrast, efforts to establish corresponding prevalence rates of specific disorders, including anxiety disorders, among young people with ID is still in its infancy. The first aim of this paper is to review this emerging literature, and detail current best estimates of the prevalence of anxiety disorders among children and adolescents with ID.
Recognition that mental health disorders not only exist, but also are highly prevalent among young people with ID has prompted interest in the development and evaluation of measures designed to identify these disorders in this population. Unique challenges associated with identifying a mental illness within the context of an intellectual disability have been identified, including, ‘diagnostic overshadowing’ – falsely attributing symptoms of mental illness to the intellectual disability (Reiss, Levitan, & Szyszko, 1982) – and the atypical and varying presentation of mental illness in this population (Bailey and Andrews, 2003, Cooper et al., 2003). Such barriers to accurate diagnosis of mental health disorders among individuals with ID have highlighted the need for a targeted approach to mental health assessment in this population. A number of comprehensive broad-based questionnaires designed to identify mental health problems in young people with ID exist (e.g. the Developmental Behaviour Checklist, Einfeld & Tonge, 2002; Nisonger Child Behaviour Rating Form, Aman, Tassé, Rojahn, & Hammer, 1996); and others designed for typically developing populations have been evaluated in young people with ID (e.g. the Child Behaviour Checklist, Achenbach, 1991a). However, the development and evaluation of measures to detect specific mental health disorders, including anxiety disorders, has received less attention. Recent reviews have provided comprehensive evaluations of existing measures for identifying anxiety (Hermans, van der Pas, & Evenhuis, 2011) and depression (Hermans & Evenhuis, 2010) in adults with ID; however studies evaluating measures in younger populations with ID are lacking. This paper aims to provide a corresponding review of existing anxiety measures evaluated in samples of children and adolescents with ID. Measures of anxiety that have been evaluated in children and/or adolescents with ID were identified and findings relating to the associated psychometric properties detailed.
Section snippets
Method
A systematic review of the literature was conducted in order to (i) identify studies that have reported prevalence rates of anxiety disorders among children and/or adolescents with ID; (ii) identify measures (questionnaires, checklists or interviews) designed to detect anxiety that have been evaluated in a sample of children and/or adolescents with ID; and (iii) document reported reliability (internal consistency, test–retest, inter-rater) and validity (convergent/divergent, criterion,
Overview of literature review
Seventy-three papers were identified from the literature search (31 from the electronic database search and 42 from the hand search) for closer review in order to determine if they met the criteria for inclusion as an anxiety prevalence study. Of these papers, 66 were excluded: 17 reported rates of mental health problems using a screening tool, 6 reported rates of mental health disorders other than anxiety disorders, 5 reported anxiety disorder diagnoses based on medical records, 36 did not
Discussion and conclusions
Relatively few studies have examined the prevalence of anxiety disorders among children and adolescents with intellectual disabilities. Among the seven studies identified in this review, the reported prevalence rate ranged from 3% to 22%. Variation in relation to rates of specific anxiety disorders was also identified. It is important to note however that the age range used across studies varied. Consistent with studies of typically developing populations, the highest rate of separation anxiety
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