INTRODUCTION

Autism spectrum disorders (ASD) are a group of biologically based neurodevelopmental disorders characterized by impairments in three major domains: socialization, communication, and behavior. The Diagnostic and Statistical Manual of Mental Disorders, 4th ed, Text Revision (DSM-IV-TR) categorizes these disorders under "pervasive developmental disorders" (PDD) [1]. These disorders include autistic disorder (classic autism, sometimes called early infantile autism, childhood autism, or Kanner's autism); Asperger disorder (also known as Asperger syndrome); and pervasive developmental disorder-not otherwise specified (PDD-NOS), including atypical autism.

The rationale for autism surveillance and screening in primary care will be reviewed here. General developmental screening, autism-specific screening tests, and clinical features, diagnosis, and management of autism spectrum disorders are discussed separately. (See "Developmental-behavioral surveillance and screening in primary care" and "Screening tools for autism spectrum disorders" and "Clinical features of autism spectrum disorders" and "Diagnosis of autism spectrum disorders" and "Autism spectrum disorders in children and adolescents: Overview of management".)

TERMINOLOGY

Autism spectrum disorders — The terms "pervasive developmental disorders" (PDD) and "autism spectrum disorders" (ASD) describe a heterogeneous group of neurodevelopmental disorders that have diverse etiologies but are characterized by constellations of symptoms involving impairments in reciprocal social interaction, communication, and behavior (specifically, stereotyped interests and activities) [1,2]. This group of disorders includes autistic disorder, Asperger disorder, and pervasive developmental disorder-not otherwise specified (PDD-NOS) [2,3]. In the Diagnostic and Statistical Manual of Mental Disorders, 4th ed, Text Revision (DSM-IV-TR), pervasive developmental disorder includes these three autism spectrum disorders, as well as Rett disorder and childhood disintegrative disorder. Rett disorder is discussed separately. (See "Rett syndrome".)

• Autistic disorder – The DSM-IV-TR provides specific criteria to diagnose autistic disorder (table 1) [1]. High-functioning autism is the term used to describe individuals with autism and an intelligence quotient (IQ) >70 (ie, borderline and above intelligence).
• Asperger disorder – The DSM-IV-TR provides specific criteria to diagnose Asperger disorder (table 2) [1]. The diagnostic criteria for autistic disorder and Asperger disorder differ only in the absence of language impairment for Asperger disorder and the requirement of presence of symptoms before age three years for autistic disorder. In contrast to autistic disorder, individuals with Asperger disorder have better facility with the mechanics of verbal expression, higher levels of cognitive function, and greater interest in interpersonal social activity [2,4]. There is some controversy regarding whether Asperger disorder is a form of high-functioning autism or a separate disorder. (See "Asperger disorder: Clinical features and diagnosis in children and adolescents".)
• PDD-not otherwise specified (PDD-NOS) – The term PDD-NOS is used to describe individuals who meet some, but not all, of the DSM-IV-TR criteria for autistic disorder (ie, atypical autism) [1,2]. Individuals may fall into this category because of late age of presentation, atypical symptoms, or subthreshold symptoms. In addition, some clinicians make an initial diagnosis of PDD-NOS in children younger than 36 months regardless of the number or severity of symptoms because diagnostic accuracy is lower in younger children.
• Rett disorder – Rett disorder is a neurodevelopmental disorder that occurs almost exclusively in females. Affected patients initially develop normally, then gradually lose speech and purposeful hand use sometime after 18 months of age. Most cases of Rett disorder result from mutations in the MECP2 gene. Characteristic features of Rett disorder include deceleration of head growth (in contrast to acceleration of head growth, which occurs in other ASD), stereotypic hand movements, and dementia. (See "Rett syndrome", section on 'Clinical features'.)
• Childhood disintegrative disorder – The essential feature of childhood disintegrative disorder (CDD), which is extremely rare, is a marked regression in multiple areas of functioning following a period of at least two years of apparently normal development. Apparently normal development is reflected in age-appropriate verbal and nonverbal communication, social relationships, play, and adaptive behavior. After the first two years of life (but before age 10 years), the child has a clinically significant loss of previously acquired skills in at least two of the following areas: expressive or receptive language, social skills or adaptive behavior, bowel or bladder control, play, or motor skills. Once symptoms develop, children with CDD have developmental profiles that are essentially identical to children with autistic disorder. CDD is often associated with an identified organic condition (eg, seizures, metabolic disorder, etc).

Surveillance — Surveillance is a process through which potential risk factors for developmental and behavioral disorders can be identified. It is defined as a flexible, continuous process in which knowledgeable professionals perform skilled observations of children during child health-care visits [5,6]. It is described in greater detail separately. (See "Developmental-behavioral surveillance and screening in primary care", section on 'Definitions'.)