Prevalence of Comorbid Psychiatric Disorders in Children and Adolescents with Autism Spectrum Disorder

This review is based on an extensive literature search to determine the prevalence of comorbid psychiatric disorders in children and adolescents with autism spectrum disorder (ASD) and shows that case reports and clinic- and community-based studies are available with which to assess this prevalence. Attention-deficit/hyperactivity disorder, anxiety disorders, and mood disorders frequently present in children and adolescents with ASD. However, a valid and reliable prevalence of comorbid psychiatric disorders in children and adolescents with ASD has not been established as a result of the limited number and small sample sizes of the reported studies.

Introduction

In 1943, Kanner¹ described a group of 11 children with a previously unrecognized disorder. He noted that these children had a number of characteristic features, such as an inability to develop relationships with people, extreme aloofness, a delay in speech development, and noncommunicative use of speech. Other features included repeated simple patterns of play activities and islets of ability. He adopted the term early infantile autism to describe this disorder and drew attention to the fact that its symptoms were already evident in infancy.

The 1980 edition of the International Classification of Diseases, 9th edition (ICD-9-CM)² of the World Health Organization and the 1980 edition of the Diagnostic and Statistical Manual of Mental Disorders, 3rd edition (DSM-III)³ of the American Psychiatric Association both set definition and diagnostic criteria for infantile autism. ICD-9-CM and DSM-III have similar definitions and diagnostic criteria for infantile autism. However, the concepts of autism are different in these two publications. In ICD-9-CM, infantile autism is classified as a subtype of “psychoses with origin specific to childhood,” whereas in DSM-III, and later in DSM-III-R,⁴ infantile autism is viewed as a type of pervasive developmental disorder (PDD), which is defined as a group of severe, early developmental disorders characterized by delays and distortions in the development of social skills, cognition, and communication.

In 1994, the American Psychiatric Association published DSM-IV,⁵ which continued to adopt the diagnostic term PDD. In DSM-IV,⁵ these disorders include: autistic disorder (AD); Rett's disorder; childhood disintegrative disorder; Asperger's syndrome (AS); and PDD not otherwise specified (PDDNOS; including atypical autism). DSM-IV⁵ also offers operational diagnostic criteria for all of the subtypes of PDD, except PDDNOS. This approach supports the taxonomic validity of each subtype and aims to facilitate research in the subclassification of these disorders. Since 1992, such a diagnostic subclassification has also been adopted in ICD-10.⁶

Despite the publication of the definition and diagnostic subclassification of PDD in DSM-IV⁵ and ICD-10,⁶ many non-medical professionals in the field of autism research prefer to use the term of autism spectrum disorder (ASD) to describe the disorders that are classified by the DSM-IV⁵ and ICD-10⁶ as AD, AS, and PDDNOS. One difference between the two diagnostic concepts (i.e., PDD and ASD) is that the PDD concept considers that AD, AS, and PDDNOS are three distinct clinical disorders, whereas the ASD concept generally considers these three disorders as a disorder on a continuum (i.e., AD as a severe form on one end, AS as a mild form on the other end, and PDDNOS as a moderate form in the middle). The recently published DSM-5⁷ has adopted the ASD concept and has set up diagnostic guidelines.

Despite the changes in diagnostic terms and criteria, the field of ASD has consistently agreed that the core features are impairment in social interaction, impairment in communication, and restricted, repetitive, and stereotyped patterns of behavior, interests, and activities. Nevertheless, many patients with ASD also develop other behavioral and/or psychiatric symptoms in addition to the core features of ASD. The additional behavioral and/or psychiatric symptoms were described by many investigators prior to the early 1990s. Simons⁸ reported in 1974 that compulsive behavior is observed in every child with a clear-cut diagnosis of autism. Ando and Yoshimura⁹ reported in 1979 that among 47 autistic children (age range 6–14 years), 36% had hyperactivity, 68% had stereotyped behavior, 43% had self-injury, and 17% had fear. In a follow-up study of autistic adult men, Rumsey et al¹⁰ reported in 1985 that 86% of these men continued to demonstrate stereotyped, compulsive behaviors, including arranging objects, and phonic tics. Le Couteur et al¹¹ in 1989 described that in 16 patients with autism (mean ± SD age 13.26 ± 3.38 years), 73% had separation anxiety, 89% had stereotyped utterances, 88% had unusual preoccupations, 55% had verbal rituals, 81% had compulsions/rituals, 69% showed hand–finger mannerisms, and 63% had unusual sensory interests. Fombonne¹² in 1992 observed that in 20 French patients with autism (age range 11–26 years), 74% showed separation anxiety, 50% had stereotyped utterances, 53% had unusual preoccupations, 16% had compulsions or rituals, 74% showed hand–finger mannerisms, and 42% had unusual sensory interests. In a follow-up study of 66 patients with autism in Hong Kong, Chung et al¹³ in 1990 noted that 47% of these children were hyperactive, 64% had poor attention and concentration, 24% showed self-injurious behaviors, 23% showed fears or phobias, 9% had depressive moods, 44% showed irritability or agitation, 29% showed inappropriate affects, 11% had sleep problems, and 8% exhibited tics.

These investigators, however, did not consider that these additional symptoms might be those of comorbid disorders and they did not specifically investigate the incidence of diagnosable psychiatric disorders based on any commonly used diagnostic criteria in their samples. This approach might be influenced by the DSM-III, DSM-IIIR, and DSM-IV diagnostic classification systems, which consider these additional symptoms as “associated features” of ASD. However, since the late 1980s there have been a number of case reports describing specific types of psychiatric disorders occurring in patients with ASD (reviewed by Tsai¹⁴ in 1996). It is conceivable that some of the “associated features” may be the diagnostic features of other coexisting psychiatric disorders. The question addressed in this review is: How frequently do these comorbid psychiatric disorders exist?