Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder marked by poor social skills, restricted interests/social interactions, and repetitive/stereotyped behaviors. The condition is termed a “spectrum” because of the wide variability in the severity of symptoms exhibited. Some patients suffer from severe impairment in language and intellectual levels, while others have normal or even advanced intellect. The etiology is not well understood and there is no known cure. Early diagnosis and intervention are important in improving the patient’s symptoms.

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Overview

Definition

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by a varying range of impairments in communication, restricted interest, and repetitive behaviors.

Epidemiology

  • Recently, worldwide incidence and prevalence have rapidly increased: 
    • Better qualification and classification of diagnostic criteria
    • Increased awareness of symptoms
    • Increased screening by primary care providers
  • Prevalence at 8 years old in the United States:
    • Overall: 1 in 54 
    • Boys: 1 in 34 
    • Girls: 1 in 145 
  • By 2 years of age, most patients show behavioral and social signs affecting home and school life.
  • Girls are more likely to exhibit intellectual disability than boys.
  • Risk factors:
    • Male gender
    • Family history (particularly siblings)
    • Chromosomal abnormalities
    • Advanced paternal and maternal age 
    • Exposure during pregnancy:
      • Toxins
      • Perinatal hypoxia
      • Prenatal infections
  • Associated conditions: 
    • Neurodevelopmental disorders:
      • Intellectual disability
      • Language disorders
      • ADHD
    • Mood disorders:
      • Major depressive disorder 
      • Self-injurious behavior
      • Aggressive behavior
      • Sleep difficulties 
    • Anxiety disorders:
      • Generalized anxiety disorder 
      • Obsessive-compulsive disorder 
    • Epilepsy 
    • Genetic disorders:
      • Tuberous sclerosis
      • Fragile X syndrome
      • Angelman syndrome
      • Rett syndrome
      • CHARGE syndrome

Pathophysiology

  • Pathogenesis is not completely understood: 
    • No evidence to support an association between immunizations and ASD
    • No evidence to support an association between parenting and ASD
  • Genetic factor:
    • Estimated median heritability: 81%
    • May be the result of interactions between multiple genes, which leads to variable expression
  • Brain abnormalities: 
    • An overall increase in brain size 
    • Functional MRI reveals abnormalities in brain regions associated with socialization (e.g., medial prefrontal cortex, amygdala).
    • Different gray- and white-matter volumes, brain chemical concentrations, and neural networks
  • Immunological factors: case reports of maternal antibodies damaging embryonic neural tissue

Clinical Presentation

Presentation of ASD varies based on the age of presentation.

  • 0–2 years:
    • A deficit or delay in social skills:
      • No social smile
      • No stranger or separation anxiety
      • Lack of pretend or symbolic play by 18 months of age
    • A deficit or delay in language:
      • No babbling by 9 months
      • No pointing or gestures
      • Lack of orientation to name by 12 months of age
      • No single words by 16 months of age 
      • Loss of language skills
  • Preschool age:
    • A deficit in social communication and interaction:
      • Lack of normal language development 
      • Slow or no response to name
      • Prefers to play alone (may be aggressive toward other children)
      • Lack of nonverbal communication 
      • Unable to sustain social interactions or share emotions/interests
      • No reaction to normal stimuli (noise, texture, smells)
    • A pattern of restricted, repetitive, and limited behaviors:
      • Repetitive motor movements (running in circles, shaking the head)
      • Resistant to changes in routine (reacts with crying/aggression)
      • Atypical play (lines up objects, opens/closes doors repeatedly, turns lights on/off repeatedly)
      • Overly attentive to parts of toys (e.g., stares at spinning wheel)
  • School-age and older:
    • A deficit in social communication and interaction:
      • Lack of normal language development
      • Lack of nonverbal communication (no eye-to-eye contact)
      • Prefers to be alone (lacks friends, does not attend social gatherings)
      • Does not understand norms of social communication
      • Anger toward the invasion of personal space
      • Unable to sustain social interactions or share emotions/interests
    • A pattern of restricted, repetitive, and limited behaviors (resists any changes in routine):
      • Atypical play (not cooperative or imaginative)
      • Abnormal response to sensory stimuli: hyper- or hyporeactivity (excessively touching other people/objects, unusually smelling other objects)

Diagnosis

Pediatricians should systematically screen children of appropriate age for ASD at well-child visits. 

  • History and physical exam, including thorough mental-status examination, are the key to diagnosis.
  • Standardized questionnaires are often utilized at 16–30 months of age:
    • Modified checklist for autism in toddlers (MCHAT)
    • Autism mental status exam (AMSE)
  • Initial assessment may also include laboratory screenings:
    • Genetic 
    • Complete metabolic panel 
    • Endocrine 
    • Infectious 
    • Toxic
  • EEG may be recommended.

Management and Prognosis

Management

  • No cure is available; rather, manage with individualized, multimodal, interdisciplinary plans.
  • Improve the core features of the disorder and target any comorbid behavioral or medical conditions. 
  • Behavioral therapy:
    • To improve social communication and help achieve independence
    • Combination of behavioral and educational modalities (e.g., family therapy)
  • Pharmacotherapy:
    • Medications to treat comorbid conditions
    • Irritability and aggression may be treated by 2nd-generation antipsychotics (e.g., risperidone).
    • Anxiety and depressive mood symptoms may be treated with selective serotonin reuptake inhibitors (e.g., fluoxetine).
    • Symptoms of hyperactivity, inattention, and impulsivity may be treated with psychostimulants (e.g., methylphenidate).

Prognosis

  • Early diagnosis and intervention improve outcomes.
  • The most prognostic factors for independent living: cognitive and verbal capacity before 6 years of age.
  • Approximately 15% of patients live independently.
  • 10%–15% of patients need community living support.

Differential Diagnosis

Table: Differential diagnoses of autism spectrum disorder
Disorder Features Differences from ASD
Intellectual disabilities
Global developmental delay Significant delay in 2 or more developmental domains (gross motor, fine motor, language, or social/cognition) Social development corresponds with the level of development of the patient
Communication disorders
Developmental language disorder
  • Persistent difficulties in language usage due to deficits in comprehension and/or production
  • Typical signs: limited vocabulary, sentence structure, and language abilities below expectations
  • Normal social interaction and communication
  • Normal play
Social communication disorder Persistent difficulty using verbal and nonverbal communications Normal behavior
Speech sound disorder Persistent difficulty with speech articulation preventing verbal communication of messages Normal social interaction and communication
Childhood-onset fluency disorder (stuttering) Disturbances in normal fluency of speech Normal social interaction and communication
Specific learning disorder
Specific learning disorder
  • Difficulty in obtaining and using academic skills (reading, writing, mathematics)
  • Appears at school age
Normal social skills and behavior
Neurodevelopmental syndromes
Rett syndrome
  • Female predominance (X linked)
  • Regression of head circumference
  • Loss of achieved milestones
  • Stereotypic hand movements
  • Gait abnormalities
  • Abnormal respiratory pattern
Normal social skills (able to maintain eye contact, laugh with others, interest in playing with others)
Tourette syndrome Sudden, repeated, nonrhythmic, stereotyped, muscle movements accompanied by sounds or vocalizations for more than 1 year Normal social skills and language
Other disorders
Disinhibited social engagement disorder
  • History of severe neglect by a caregiver
  • Marked by overfamiliarity and ease in approaching strangers
  • Normal behavior and language
  • Social deficits tend to improve in an appropriate caregiving environment.
Reactive attachment disorder
  • History of severe neglect from a caregiver
  • Decreased emotional response
  • Normal behavior and language
  • Social deficits tend to improve in an appropriate caregiving environment.
Schizoid personality disorder
  • Onset after 18 years of age
  • Marked by a lifelong pattern of social detachment
No stereotyped behavior
Hearing impairment No language development Normal social interaction and communication
ASD: autism spectrum disorder

References

  1. World Health Organization. The ICD-10 Classification of Mental and Behavioural Disorders. Clinical descriptions and diagnostic guidelines. www.who.int/classifications/icd/en/bluebook.pdf   
  2. Landa RJ, Gross AL, Stuart EA, Faherty A. Developmental trajectories in children with and without autism spectrum disorders: the first 3 years. Child Dev. 2013 Mar-Apr  https://pubmed.ncbi.nlm.nih.gov/23110514/ 
  3. Maglione MA, Gans D, Das L, Timbie J, Kasari C; Technical Expert Panel; HRSA Autism Intervention Research – Behavioral (AIR-B) Network. Nonmedical interventions for children with ASD: recommended guidelines and further research needs. Pediatrics. 2012 Nov https://pubmed.ncbi.nlm.nih.gov/23118248/ 
  4. Myers SM. Management of autism spectrum disorders in primary care. Pediatr Ann. 2009 Jan https://pubmed.ncbi.nlm.nih.gov/19213293/ 
  5. Sadock BJ, Sadock VA, & Ruiz P. (2014). Kaplan and Sadock’s synopsis of psychiatry: Behavioral sciences/clinical psychiatry (11th ed.). Chapter 31, Child psychiatry, pages 1152-1169. Philadelphia, PA: Lippincott Williams and Wilkins.
  6. Pedapati E. (2017). Autism spectrum disorders and their clinical management. DeckerMed Medicine. doi:10.2310/im.13008

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