Intellectual disability (ID) is defined as a full scale intellectual quotient (IQ) less than two standard deviations (< -2SD) below the mean, which corresponds to a raw score of < 70 or a percentile of < 2%. ID can be classified as mild (FSIQ 55-69), moderate (40-54), severe (25-39) or profound (< 25).
It is distinct from, and exclusive to, learning disorders. Note that learning difficulties and autism spectrum disorders are difficult to diagnose in the setting of ID. Note that different nomenclature exists in different parts of the world.
Intellectual disability may be isolated, with no known underlying cause, or may be associated with different syndromes, developmental delay and/or various generic abnormalities. Investigations for underlying causes may be undertaken after paediatric assessment.
The diagnosis of ID requires a cognitive assessment (e.g. WIPPSI, WISC) and cannot be made via clinical observation. A child must also undergo a thorough history and examination for underlying causes, associated syndromes and genetic abnormalities, developmental difficulties and other associated problems (e.g. ADHD, behavioural problems). A website exists for determining treatable causes of ID.
A formal diagnosis of ID will gain funding for a child through the Department of Education & Early Childhood Development (DEECD) or the Catholic Education Department, although also requires a Adaptive Behavioural Composite Score (Vanderbilt) < 70. A formal diagnosis if ID will also allow access to specialist schooling, if required.
- A diagnosis of ID requires a full scale IQ < 70 (< -2SD or < 2%) on formal cognitive assessment.
- A formal diagnosis of ID will gain funding for a child through school services, as well as allow access to specialist schooling.
- Cognitive assessment can be undertaken through school services (DEECD or Catholic Education Department) or via private psychology services
- The child should also undergo a thorough history and examination for underlying causes, associated syndromes and genetic abnormalities, developmental difficulties and other associated problems (e.g. ADHD, behavioural problems).
- It is also important to exclude hearing and visual difficulties.
- A screening panel for underlying organic pathology is recommended in the workup of a child with intellectual disability. Although there is no ‘standard’ panel of investigations, this should include genetic testing and should be undertaken after assessment with paediatric services.
- Management for ID centres around provision of support services, particularly educational and developmental, as well as screening for co-morbidities.
- Medications have no role in the management of intellectual disability alone, although may be of use in some co-morbidities.
- Referral to paediatric outpatient services is appropriate for further assessment in proven or suspected intellectual disability.
- Information to bring to any appointments:
- recent school reports and any written reports from teachers
- any testing (cognitive, learning, etc)
- behavioural questionnaires (if done)
- reports from any psychologists or other allied health services
- any previous blood tests performed
- Children with intellectual disability receive funding through the National Disability Insurance Scheme to support developmental and functional progression - please see the Early Intervention Services page for more detail.
- Allied health services
- Several allied health services will be appropriate to support children with ID including psychology, speech pathology, occupational therapy.
- Assessment services
- Further resources
- Behaviour Support Services through the Department of Health & Human Services (DHHS) provides behavioural support in the home environment for families of children with ID.
- Funding can be accessed through a Carers Allowance for those with a FSIQ < 55, as well as those with some underlying syndromes.
- Disability Services provides government funded specialist disability supports for people with disabilities and their families.