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Dual diagnosis: Assessment and diagnosis

Diagnosing mental health problems in someone with a developmental disability requires information from various sources and settings.

People with developmental disabilities can develop the same mental health problems as the general population, but they may have more difficulty communicating their experiences and discomforts. This challenge may lead to misdiagnosis and inappropriate treatment. For example:

  • symptoms of mental health disorders may be misattributed to the developmental disability (diagnostic overshadowing)
  • medical/neurological problems may be seen as symptoms of a mental health disorder.


There are steps that clinicians can take to better understand how biological, psychological and social factors affect a person's mental health. These steps include asking the following four questions (Bradley & Burke, 2002):

  • Is there a medical problem?
  • Is there a problem with supports and appropriate expectations?
  • Is there an emotional problem?
  • Is there a psychriatric disorder?

Watch: Dr. Yona Lunsky talks to families and caregivers about the need for comprehensive assessment

Medical problems

Many people with developmental disabilities have physical health concerns that can go unnoticed or undertreated. For example, a person who is constipated but unable to communicate the pain to others may become aggressive while in pain and lash out at others. A full physical exam, and regular vision and hearing tests and dental checkups are essential to rule out medical causes of problem behaviours.

Supports and appropriate expectations

After physical problems have been checked for and treated, it is important to examine how the support the person is receiving – or not receiving – influences their behaviour. Does the person have needs that are not being met?

  • A person who is unable to do the things that are meaningful or expected of them may become anxious, angry or sad.
  • The person may be frustrated because they get too much help from others and are not given the independence they desire.  

Discuss with service providers how services can be optimized to meet the person's  needs.

Emotional problems

There is a difference between experiencing intense negative emotions and having a psychiatric disorder. Intense feelings such as anger, sadness or anxiety, and the behaviours that go with them, may be responses to stress, trauma or grief. If these emotional problems remain unresolved, they can develop intor psychiatric disorders.

Psychiatric disorders

There is no clear line that indicates when problems become severe enough to be described as a psychiatric disorder in people with developmental disabilities. If emotional problems are not recognized and addressed, they can become more intense and severely affect the person and those around them.

In addition to using the Diagnostic and Statistical Manual of Mental Disorders (DSM), clinicians who work with people with developmental disabilities use the Diagnostic Manual–Intellectual Disability (DM-ID-2), which suggests adaptations to the DSM-IV for people with intellectual disabilities. Clinicians may also use the Diagnostic Criteria in Learning Disability (DC-LD)  to help screen and assess people for psychiatric disorders.

A Guide to Understanding Behavioural Problems and Emotional Concerns In Adults with Developmental Disabilities (DD) for Primary Care Providers (developed by the Developmental Disabilities Primary Care Initiative) outlines steps to identifying the causes of behavioural problems and includes a template for recording observations and data.

Developmental disabilities toolkits for clinicians


Implementing health checks for adults with developmental disabilities

This toolkit provides primary care providers with tools and resources to support the provision of health checks for patients with developmental disabilities. 

Improving emergency care for adults with developmental disabilities: A toolkit for providers

Topics covered:

  • Identifying your patients and alerting the team
  • Adapting clinical approaches
  • Enhancing clinical approaches

Includes tools, tip sheets and videos for clinicians and patients.



Developmental disabilities and mental health

A self-directed online course explores the health needs of adults with developmental disabilities (DD), and the contributing factors that account for disparities in health and health care between adults living with DD and those in the general population.

The course addresses the role of primary care providers and the Canadian recommended guidelines and practice tools.