Hearing Impairment in Adults with an Intellectual Disability: epidemiology and rehabilitation

In this thesis, the results are presented of an epidemiological study of hearing impairment in adults with an intellectual disability (ID), as well as the results of a study on the implementation of an audiological rehabilitation protocol in centres for persons with an ID. It is preceded in chapter 1 by a review of literature on epidemiology and rehabilitation of hearing impairment in persons with an ID. Moreover in this chapter is explained why these studies were established. In addition, aims of the study are formulated, and definitions given for intellectual disability, hearing impairment, visual impairment, dual sensory impairment and implementation. The few studies on prevalence of hearing impairment in adults with an ID, that thus far have been published, were performed in small or selected populations. In addition, different definitions of hearing impairment were used. In order to be able to estimate prevalence and severity of hearing impairment on a nationwide level, a large scale study was established in 1998. This study, described in chapter 2, was performed in a random sample of 1598 adults from a base population of 9012 adult ID service users. This base population was representative for the total population of adult ID service users in the Netherlands. Internationally accepted diagnostic methods and criteria were used. After a re-weighting procedure for non-attenders and a stratification that was applied, a prevalence of hearing impairment of 30% could be estimated for the total population of adult ID-service users. This high prevalence was not only accounted for by the frequently occurring hearing impairment in persons with Down syndrome (prevalence 57%), but also by a prevalence of 24% in the subpopulation with an ID by a different cause, which appeared to be significantly higher than the prevalence of 16-17% in the general population. Apart from the raised prevalence, in the latter subpopulation it also appeared that the prevalence-versus-age curve was shifted one decade forwards to a younger age. Because of this, we want to advise to adjust existing guidelines for hearing screening in adults with an ID by a different cause than Down syndrome: hearing screening on presbyacusis should take place from the age of 40 years instead of 50 years.

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