Text adapted from "Intellectual and developmental disabilties" in Psychiatry in primary care by Yona Lunsky and Johanna Lake, (CAMH, 2019).
It is common for health care practitioners to misattribute symptoms of psychiatric disorder to IDD, which means that psychiatric symptoms are often ignored and therefore untreated. Adults with IDD are at greater risk of developing psychiatric disorders, which, if left untreated, can lead to very serious complications.
Know your normal
The concept of knowing one’s baseline or “normal” is very important when working with people with ASD or IDD more generally. Comparing how your patient is currently doing (e.g., emotionally, physically) to how the patient has been before can help to determine whether a psychiatric disorder is present. Comparing reported symptoms to a set of diagnostic criteria may be less useful when the patient is unable to report reliably on symptom history or when symptoms are atypical. For example, it is widely recognized that sleep patterns are impaired in many people with ASD, but more important than knowing how much sleep the person is getting is finding out whether there has been a substantial change in sleep patterns.
ASD is also associated with high levels of anticipatory anxiety and predictability is very important. This means that differentiating between ASD symptoms and an anxiety disorder can be complicated.
The “Know Your Normal” toolkit was developed as part of the Ambitious about Autism campaign for young adults with ASD in the United Kingdom. It guides youth to know what their normal is, so they can explain it to others, including health care practitioners, and so they can recognize when they are feeling and behaving in ways that are not typical for them.
Common co-occurring psychiatric disorders
Mood and anxiety disorders tend to be under-diagnosed in people with IDD. Some of the typical screening questions for these disorders rely on a sense of time, as well as on the ability to report thoughts and subjective experiences, which can be difficult for some people with IDD. If the patient’s communication is more limited, use questionnaires with simplified language or visuals, and focus on observable behaviours, as well as on gathering collateral information.
The Glasgow Depression Scale is a brief self-report depression tool for people with IDD, which also has a 16-item carer supplement form (Cuthill et al., 2003). The Glasgow Anxiety Scale is similar in structure, but does not have an informant version (Mindham & Espie, 2003).
Many clinicians do not screen for addictions because they assume that people with IDD would not be interested in or exposed to alcohol and other drugs. However, population data suggest that addictions are as common among people with IDD as they are among people without IDD, particularly in adults with more mild disabilities who live independently. This means that you should screen for addictive behaviours and not assume that they are absent because of the disability.
Psychotic disorders are more common in adults with IDD than in other adults, but they can be over-diagnosed in people with IDD. A person may behave in a psychotic manner in response to stress, and odd behaviour may also be part of the baseline or “normal” in terms of the person’s cognitive or social functioning. This means that you need to know how your patient typically behaves, and is especially relevant for patients with ASD who may exhibit negative symptoms (e.g., affective flattening, social withdrawal), but which can also present in patients with an intellectual disability. Using self- talk as a way of coping or having an imaginary friend may be mistaken for auditory hallucinations and delusions.