CHAPTER 132

Autism Spectrum Disorder

Robin Steinberg-Epstein, MD

Autism spectrum disorder (ASD) is characterized by impairments in social communication as well as restrictive, repetitive, and stereotypic behaviors or interests. According to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5), a person with ASD must display persistent communication, interaction, and behavioral challenges across multiple contexts. These disturbances must be present early on but may not be apparent until social demand exceeds the limitation. These characteristics must cause significant impairment and cannot be caused by cognitive impairment (Box 132.1). Cognitive impairment is often a comorbidity, however.

This new term, ASD, includes the previous terminology of autistic disorder, Asperger syndrome, and pervasive developmental disorder–not otherwise specified; the term ASD no longer includes Rett syndrome. Although criteria differ somewhat, all these disorders had in common an impairment in social communication and repetitive or unusual interests of varying degrees. These disorders require similar management and treatment, and assessing the level of impairment is somewhat subjective. Therefore, a single term— ASD—best incorporates all those individuals who are significantly affected by its symptomatology.

Epidemiology

As recently as 1999, the prevalence of ASD was thought to be 1 in 2,500. More recent numbers from the Centers for Disease Control and Prevention published in 2014 cite a prevalence of 1 in 59 children in the United States. The prevalence in Europe, Asia, and North America averages between 1% and 2% of the overall population. Boys are affected approximately 4 times as often as girls, which equates to 1 in every 38 boys. Affected girls are often more impaired than boys, however. Autism is considered the fastest-growing developmental disability. This increase is, in part, the result of an understanding of a broader phenotype.

Derived from Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition.

Clinical Presentation

Autism spectrum disorder is truly a spectrum of social communication deficits. Although a certain set of behaviors defines the disorder, any child may have any combination of the symptoms that result in the same outcome—severe and incapacitating social deficits. Furthermore, the challenges experienced by this population are more than just developmental delays; the behaviors of these individuals are aberrant and odd.

Many children with an ASD have difficulty with eye contact and body posture. Even those who have some eye contact often do not use their eyes to convey a social message. They may look out of the corner of their eyes, focus only on the lips of the speaker, or look only infrequently. In other words, they may make eye contact but at the wrong time. They may talk to others with their bodies facing away from them. They may not gesture to help clarify intention.

Whereas some children have limited communication, some offer too much information. They may be quick to talk to others about things they are interested in but be unable to talk to their conversational partner about that person’s own interests. They seem socially insensitive. As younger children, they are often entertained by their own interests for long periods. Some have limited need for relationships, but others desire interaction but do not understand how to initiate or maintain interactions. Although some of these children are nonverbal, some repeat or echo what they hear from movies, television, or nearby conversation. Others seem able to converse but have trouble with social banter. It is important not to be deceived by a child who interacts with others or even gives hugs but only on the child’s own terms.

Children with ASD often have a fascination with patterns. The pattern may be in the form of household routines or within a particular subject area. This may manifest in an obsession for sameness and resistance to change or an obsessive need to know everything about a certain topic. Many know all there is to know about such favorite topics as Thomas the Tank Engine or dinosaurs from the Jurassic Period but cannot answer a question such as, “How are you?” or “What is your name?” They may be upset by a road detour or a furniture rearrangement. Some of these children, because of an incredible ability to recognize patterns, can read as early as 2 years of age, even though they can neither speak functionally nor comprehend what they read.

A significant portion of children have difficulty with sensory processing. This takes the form of problems with smells, tastes, sounds, sights, and touch. This symptom may be manifest in the need to taste everything, including nonfood items; covering ears in loud situations; or an inability to tolerate tags in clothing.

A huge variation exists in cognitive ability. The severity of ASD is independent of cognitive ability. Although approximately 25% of those with ASD have intellectual disabilities, many are of normal intelligence and some are gifted.

Parents or caregivers often raise behavioral concerns. It is important to recognize red flags and behaviors that demand further evaluation (Boxes 132.2 and 132.3). That is, certain classic symptoms exist, but the physician must be mindful of the child who is simply unable to connect with others. Physicians should rely on their own instincts. Inconsistent symptoms are the hallmark of this disorder. Some parents or guardians of children with an ASD describe a phenomenon whereby the children are developing normally until 12 to 15 months of age and then suddenly lose skills or stop progressing. This finding is particularly concerning.

Pathophysiology

Numerous proposed etiologic possibilities for the origins of ASD exist, from the inbreeding of computer “whizzes” to exposure to microwaves. However, no consistent explanation or pattern has emerged. It is known that the structure of the brain is different, but the reason why remains unknown.

Derived from Filipek PA, Accardo PJ, Baranek GT, et al. The screening and diagnosis of autism spectrum disorders. J Autism Dev Disord. 1999;29(6):439–484.

Up to 10% of those with ASD have another medical condition that might have led to this disorder (Box 132.4). This leaves 90% of patients without an etiology, however.

Genetics seem to play an important role in the development of ASD. A risk of the disorder among siblings of up to 20% has been reported, which is more than 10 times the risk in the normal population. Family members are more likely to exhibit social deficits, anxiety, or depression than are family members who do not have a relative with the disorder. Several candidate chromosomes have been suggested as being associated with this disorder, but no 1 locus is responsible for this disorder.

It is also important to realize that up to 30% of children with ASD have abnormalities on electroencephalography (EEG). This finding may point to the structural abnormalities in an autistic brain but does not seem to account for the disease itself. The epileptiform changes should be evaluated by a neurologist to determine if medication is indicated. Without an outward expression of seizures, however, many patients do not opt for treatment.

Several environmental markers have also been suggested as being linked to ASD, but most have not proved credible. Major epidemiologic studies within the United States and internationally have examined the roles of vaccinations, diet, and thimerosal preservative in the development of this disorder. None of these studies has found proof to support these theories. Known associations include older paternal age, preterm birth, and jaundice. Several studies have suggested that pollution may play an epigenetic role.

Much of the newer research suggests a fundamental neurobiologic difference in the prefrontal cortex, which likely occurs as the result of abnormal neuronal overgrowth in the first 20 weeks of gestation. This suggests a genetic or epigenetic etiology before birth in 90% of patients with autism.

Children with ASD should undergo routine health maintenance, including all recommended immunizations. No evidence exists linking ASD with immunizations.

Differential Diagnosis

Few entities present with impairment in the same 2 domains as those that are affected by ASD. A limited number of disorders mimic ASD (Box 132.5). However, several disorders exist that commonly occur with ASD that, if not identified, make treatment more difficult (Box 132.6).

Evaluation

No single diagnostic test, blood or otherwise, can confirm the diagnosis of ASD. Diagnosis is based on history, interaction with the child, and meeting DSM-5 criteria.

History

Regular developmental surveillance and screening should be part of every well-child evaluation, especially between ages 9 and 30 months. In 2019, the American Academy of Pediatrics recommended that pediatricians conduct developmental and behavioral surveillance during all well child visits, developmental screening at the 9-, 18-, and 30-month visits, and standardized screenings of patients for ASD at 18 and 24 month. Special attention should be given to a child who has a sibling with ASD or a child whose parent or caregiver has expressed concern. Several standardized screening tools can be used, including the Parents’ Evaluation of Developmental Status or the Ages and Stages Questionnaire, to identify developmental and social competency skills and concerns. The Modified Checklist for Autism in Toddlers, Revised, with Follow-Up (M-CHAT-R/F) is an excellent autism-specific screening tool with moderate sensitivity and high specificity for use at the 18- and 24-month visits to identify individuals at high risk for ASD. A positive M-CHAT-R/F screening is associated with ASD in 50% of patients and with developmental delay in 90% of patients. These screening tools are quick and easy and can be completed by the parent or caregiver in the waiting area or with minor assistance from office personnel.

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