Studies have consistently reported an association between ASD and internalizing symptoms, in particular, anxiety and depression. A bidirectional association has been identified between internalizing disorders and autistic symptoms. For example, both a higher prevalence of anxiety disorders has been found in ASD and a higher rate of autistic traits has been reported in youth with mood and anxiety disorders. Individuals with ASD also display more social anxiety symptoms compared to typical individuals, even if these symptoms were clinically overlapping with the characteristic social problems of ASD. In addition, there is some evidence to suggest that adolescents and young adults with ASD show a higher prevalence of bipolar disorders as compared to controls.
Depression is one of the most common comorbid conditions observed in individuals with ASD, particularly higher functioning youth. A study of psychiatric comorbidity in young adults with ASD revealed that 70% had experienced at least one episode of major depression and 50% reported recurrent major depression. Although another documented association is with obsessive-compulsive disorder (OCD), it is difficult to determine whether observed obsessive-repetitive behaviors are an expression of a separate, comorbid OCD, or an integral part of the core diagnostic features of ASD (i. e., restricted, repetitive patterns of behavior, interests, or activities).
An association between ASD and attention-deficit/hyperactivity disorder (ADHD) and other externalizing problems (i. e., oppositional defiant disorder) have been reported. Studies have found that children with ASD in clinical settings present with co-occurring symptoms of ADHD with rates ranging between 37% and 85%. Although there continues to a debate about ADHD comorbidity in ASD, research, practice and theoretical models suggest that co-occurrence between these conditions is relevant and occurs frequently. For example, case studies suggest that ADHD is a relatively common initial diagnosis in young children with ASD. It is also important to note that a significant change in the DSM-5 is removal of the DSM-IV-TR hierarchical rules prohibiting the concurrent diagnosis of ASD and ADHD. When the criteria are met for both disorders, both diagnoses are given.
Tourette Syndrome (TS) and other tic disorders have been found to be a comorbid condition in many children with ASD. A Swedish study showed that 20% of all school-age children with ASD met the full criteria for TS. There also appears to be a higher incidence of seizures in children with autism compared to the general population. The comorbidity of ASD and psychotic disorders has received some research attention. A study of children with ASD who were referred for psychotic behavior and given a diagnosis of schizophrenia showed that when psychotic behaviors were the presenting symptoms, depression and not schizophrenia, was the likely diagnosis. Thus, individuals with ASD may present with characteristics that could lead to a misdiagnosis of schizophrenia and other psychotic disorders.
Children and youth with ASD frequently have comorbid conditions, with rates significantly higher than would be expected from the general population. The most common co-occurring diagnoses are anxiety and depression, attention problems, and disruptive behavior disorders. The core symptoms of ASD can often mask the symptoms of a comorbid condition. The current challenge for practitioners is to determine if the symptoms observed in ASD are part of the same dimension (i. e, the autism spectrum) or whether they represent another condition. Although various psychometric instruments, such as clinical interviews, self-report questionnaires and checklists, are widely used to assist in diagnosis, these tools are designed and standardized to identify symptoms in the general population, and may not be appropriate and valid for use with ASD. Likewise, their administration may be problematic in that individuals with ASD may have difficulties in sustaining a reciprocal conversation, reporting events, and lack an understanding and empathy for the feeling of others. Nevertheless, comorbid problems should be assessed whenever significant behavioral issues (e.g., inattention, impulsivity, mood instability, anxiety, sleep disturbance, aggression) become evident or when major changes in behavior are reported. Co-occurring conditions should also be carefully investigated when severe or worsening symptoms are present that are not responding to intervention or treatment.
Mazzone et al.: Psychiatric comorbidities in asperger syndrome and high functioning autism: diagnostic challenges. Annals of General Psychiatry 2012 11:16. doi:10.1186/1744-859X-11-16
Lee A. Wilkinson, PhD, is a licensed and nationally certified school psychologist, chartered psychologist, registered psychologist, and certified cognitive-behavioral therapist. He is also a university educator and trainer, and has published widely on the topic of autism spectrum disorders both in the US and internationally. Dr. Wilkinson is author of the award-winning book, A Best Practice Guide to Assessment and Intervention for Autism and Asperger Syndrome in Schools, published by Jessica Kingsley Publishers. He is also editor of a recent volume in the American Psychological Association (APA) School Psychology Book Series, Autism Spectrum Disorder in Children and Adolescents: Evidence-Based Assessment and Intervention in Schools, and author of Overcoming Anxiety and Depression on the Autism Spectrum: A Self-Help Guide Using CBT. His most recent book is A Best Practice Guide to Assessment and Intervention for Autism Spectrum Disorder in Schools (2nd Ed.).