Depression is more prevalent amongst people with intellectual disabilities than in the general population. People with all levels of Intellectual Disability have been described as suffering from mood disorders, systematic, prospective, well-controlled studies with reliable means of assessing the presence of these disorders have not been conducted with representative samples of persons with ID.
However, there is a general consensus that the diagnostic criteria for depressive disorders in DSM-IV-TR (Diagnostic and Statistical Manual of Mental Disorders, American Psychiatric Association, 1994) apply to people with ID, especially in the higher levels of cognitive functioning. One of the main problems in diagnosing these disorders in persons with severe and profound Intellectual Disability is that people with such disabilities have either limited or non-verbal communication, cannot express subjective feelings such as lack of pleasure, or material which is primarily ‘internal’. Another factor that imposes a challenge in the diagnosis of these disorders in this population is that persons with ID are a highly heterogeneous group. Thus, great variations exist in the levels of cognitive and social skills amongst individuals within the same level of functioning, as well as at the different cognitive levels (mild to profound). Therefore, there has been concern that depressive disorders are not properly recognized in this population and remain under-diagnosed.
A study concluded that existence of depression was high in people with Intellectual Disability. The current American classification system for mental diseases (DSM-IV-TR, (Diagnostic and Statistical Manual of Mental Disorders, American Psychiatric Association, 1994) 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). 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
_ Considerable weight loss or gain
_ Insomnia or hypersomnia
_ Psychomotor agitation or retardation
_ Fatigue or loss of energy
_ Feelings of worthlessness
_ diminished ability to think or concentrate
_ Recurrent thoughts of death