Prevalence of Co-Morbid Psychiatric Conditions In An Adult Population Assessed for Autism Spectrum Disorder

Background:  

Individuals with an autism spectrum disorder (ASD) are vulnerable to co-morbid mental health problems. However, research in this area typically involves children and there is limited research investigating co-morbid difficulties in adults with ASD.

Furthermore, to date, no studies have investigated the relationship between ASD subtypes (Asperger, Childhood Autism, atypical autism and PDD-NOS) and the risk of developing co-morbid conditions in adulthood.

Objectives:  

To determine prevalence and type of co-morbid mental health conditions in adults diagnosed with ASD.

Methods:  

A retrospective review was completed of 518 adult patients (78% male; mean age: 31 years, SD: 11 years) consecutively diagnosed with ASD at the Behavioural Genetics Clinic, a specialist clinic providing gold-standard assessment of ASD in adults at the Maudsley Hospital, London. Diagnostic assessment included a detailed neuropsychiatric interview, the Autism Diagnostic Interview-Revised (ADI-R) and / or Autism Diagnostic Observation Schedule (ADOS), pending consent to contact parents/parental availability, and a physical examination.  Co-morbid mental health diagnoses were made in accordance with ICD10 criteria (with the exception of adult Attention Deficit Hyperactivity Disorder (ADHD) which, in keeping with UK guidelines, was assessed using DSM IV).

Results:  

394 (76%) patients that were diagnosed with ASD also met diagnostic criteria for at least one other co-morbid mental health condition.  The most common of these were depression (19%), Obsessive Compulsive Disorder (OCD; 18%), Generalised Anxiety Disorder (GAD; 13%), social phobia (11%) and ADHD (9%).

Rates of different co-morbid conditions (depression, OCD, GAD, social phobia and ADHD) were contrasted between ASD subtypes using Pearson chi-square.  Those meeting diagnostic criteria for Asperger or Childhood Autism (N = 351) had a significantly lower prevalence of co-morbid ADHD (p = .05) and a significantly higher prevalence of co-morbid OCD (p = .02) than people diagnosed with PDD-NOS or atypical autism (N = 173). Furthermore, individuals with Asperger (N = 218) exhibited significantly higher rates of social phobia (p = .02) and depression (p = .05) than those with Childhood Autism (N = 133).  There were no significant differences in rates of any other co-morbid conditions between ASD subtypes. 

Conclusions:  

Results from this large retrospective naturalistic sample indicate that adults with ASD have a significantly increased risk for developing co-morbid mental health conditions, highlighting the need for improved recognition and treatment of co-morbid mental health difficulties in this population.   Our results also have implications for the diagnostic formulation of ASD and other psychiatric conditions.  For example, the notion that diagnoses of co-morbid psychiatric conditions such as ADHD should not be made if an individual is on the autistic spectrum is challenged.  Also, subtypes of ASD differed with respect to likelihood of developing specific psychiatric conditions.