8.4.2 Presentation and Diagnosis
The Presentation and Diagnosis of Psychiatric Illness and Behavioural Disorder in People with Intellectual Disability, Including the Concept of Diagnostic Overshadowing
The presentation and diagnosis of psychiatric illness and behavioural disorders in people with intellectual disabilities can be challenging due to their cognitive and communication impairments. The diagnosis may be complicated by the presence of co-morbid medical conditions, sensory impairments, and the use of psychotropic medications. Moreover, the concept of diagnostic overshadowing can occur, which refers to the tendency to attribute behavioural changes to an individual’s intellectual disability rather than considering an underlying psychiatric condition (Reiss & Valenti-Hein, 1994).
During the evaluation of individuals with intellectual disabilities (ID), it is crucial to consistently account for coexisting psychiatric conditions, as they are frequently observed and manageable. Psychiatric disorders are often overlooked in the ID population due to diagnostic overshadowing, where symptoms of mental illness are erroneously ascribed to the ID. In 2001, the Royal College of Psychiatrists introduced the diagnostic criteria for individuals with ID (DC-LD) to assist in identifying mental illnesses within the ID population.
| Psychiatric Condition | Information |
| Schizophrenia | ~3x more common; earlier onset (mean 23 years); associated with epilepsy, negative symptoms, episodic memory impairment; aggression in severe ID |
| Bipolar Affective Disorder | Prevalence 2-12%; diagnostic challenges in severe ID; symptom equivalents: hyperactivity, wandering, mutism, temper tantrums |
| Depressive Disorder | Often overlooked; marked biological features; suicidal thoughts/acts in borderline/moderate ID; consider other causes of mood disturbance |
| Anxiety Disorders | Difficult to distinguish from depression except for situational features |
| Obsessive-Compulsive Disorder (OCD) | Higher prevalence; differential diagnosis: ritualistic behaviours, tic disorders, autism/Asperger’s disorder manifestations |
| Attention Deficit Hyperactivity Disorder (ADHD) | Prominent in children with ID (up to 20%); stimulants may help in mild ID; limited efficacy in severe/profound ID |
| Personality Disorder | Difficult to define; ~20% prevalence in mild/moderate ID inpatient population |
Psychiatric illness and behavioural disorders in individuals with intellectual disabilities can present in various ways, including aggression, self-injury, anxiety, depression, and psychosis (Emerson & Baines, 2010). The presentation may be atypical or subtle, making the diagnosis challenging. It is essential to consider the individual’s level of intellectual functioning, communication abilities, and social environment when making a diagnosis.
Diagnostic overshadowing:
Diagnostic overshadowing is a common problem that can lead to under-diagnosis or misdiagnosis of psychiatric conditions in individuals with intellectual disabilities. This can result in inappropriate or inadequate treatment and a lower quality of life for the individual (Reiss & Valenti-Hein, 1994). Healthcare professionals should be aware of this phenomenon and take steps to avoid it. This includes considering the possibility of underlying psychiatric conditions and conducting a thorough assessment using specialized assessment tools and techniques.
In summary, the diagnosis of psychiatric illness and behavioural disorders in individuals with intellectual disabilities can be challenging due to their cognitive and communication impairments. Healthcare professionals should be aware of the concept of diagnostic overshadowing and take steps to avoid it by considering the possibility of underlying psychiatric conditions and conducting a thorough assessment using specialized assessment tools and techniques.
References:
- Emerson, E., & Baines, S. (2010). Health inequalities and people with learning disabilities in the UK. Tizard Learning Disability Review, 15(3), 14-21.
- Reiss, S., & Valenti-Hein, D. (1994). Attributions of mental retardation: Effects on psychotherapeutic outcome. American Journal of Mental Retardation, 99(1), 53-64.