Depression, anxiety and adjustment disorders are particularly more prevalent amongst people with intellectual disabilities (ID) than in the general population (Richards et al., 2001; Tu & Zellweger, 1965). This is the case for most psychiatric disorders (Einfeld, 1992; Gitta & Goldberg, 1995; King et al., 1994; Singh, et al., 1991; Sovner and Horley, 1989; Stavrakaki and Mintsioulis, 1997; Vitello and Behar, 1992). King et al. (1994) found that the most common diagnoses in individuals with ID at the Landerman Developmental Center in California were impulse control disorders, stereotypical/habit disorders, anxiety disorders and mood disorders. In a similar study in Canada, Gitta (1995) concluded that co-existence of anxiety disorders, adjustment disorders and depression was high in people with ID.
This chapter describes the main clinical aspects of depression, anxiety and adjustment disorders and considers the similarities and differences of the three conditions in people with ID.
The current American classification system for mental diseases (DSM-IV-TR, (Diagnostic and Statistical Manual of Mental Disorders, Amercian Psychiatric Association, 1994; Diagnostic and Statistical Manual of Mental Disorders, American Psychiatric Association 2000)), includes two types of depressive disorders:
(a) major depressive disorders, and
(b) dysthymic disorders.
Major depressive disorder is characterized by one or more major depressive episodes (i.e. at least two weeks of depressed mood or loss of interest). According to this classification, five or more of the following symptoms of depression must be present during the same two-week period for a diagnosis of major depressive disorder to be made:
depressed mood most of the day
markedly diminished interest or pleasure in all activities