What is the diagnostic approach for autism spectrum disorder (ASD) in adults?

Diagnosing Autism Spectrum Disorder in Adults

Diagnosis of ASD in adults requires a comprehensive psychiatric assessment by a trained professional using standardized diagnostic tools, focusing on childhood symptom onset, persistent social-communication deficits, and restricted/repetitive behaviors, supplemented by collateral history from family members when possible. 1

Core Diagnostic Approach

Initial Screening and History

• Screen for core ASD symptoms including impaired social relatedness and repetitive or unusual behaviors during the initial evaluation 1
• Obtain a thorough developmental history documenting symptom onset in childhood, as ASD is a neurodevelopmental disorder requiring early-life manifestation 1, 2
• Conduct structured interviews with both the individual and family members (when available) to gather collateral information about developmental trajectory and current functioning 1
• Review all available past records, including school reports, prior evaluations, and medical documentation 1

Standardized Diagnostic Measures

• Use objective criteria and standardized tools administered by professionals specifically trained in autism diagnosis 1
• The Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) has 91% sensitivity and 76% specificity for ASD diagnosis 3
• The Autism Diagnostic Interview has 80% sensitivity and 72% specificity 3
• The Autism Clinical Interview for Adults (ACIA) is a newer tool designed specifically for adult populations, taking 60-90 minutes to complete and covering both core autism characteristics and co-occurring conditions 4

Key Clinical Features to Assess

Social-Communication Domain:

• Evaluate patterns of eye contact, use of gestures, and facial expressions in social contexts 5
• Assess reciprocity in social interactions and ability to maintain social closeness 5
• Document difficulties with understanding social cues and maintaining relationships 2

Restricted/Repetitive Behaviors:

• Identify circumscribed, intense interests that may dominate the person's time and attention 3
• Look for repetitive motor behaviors or "stimming" (self-stimulatory behaviors), which significantly affect mental health 5
• Assess for rigid adherence to routines or rituals 2

Camouflaging Behaviors:

• Recognize that many adults, particularly women and older adults, may "camouflage" or mask their autism symptoms, making diagnosis more challenging 5, 2
• This disguising of typical autism behaviors can lead to missed or delayed diagnoses in underdiagnosed populations 2

Medical and Genetic Evaluation

Essential Medical Workup

• Perform a comprehensive physical examination, including Wood's lamp examination to screen for tuberous sclerosis 3
• Consider genetic consultation, as clinical genetics evaluation identifies an underlying etiology in 30-40% of individuals with ASD 3

Tiered Genetic Testing

• First tier: High-resolution chromosomal analysis, DNA testing for Fragile X syndrome (1-5% yield), and examination for dysmorphic features 6, 1
• Second tier: Chromosomal microarray (10% diagnostic yield), MECP2 gene testing (4% yield in females), and PTEN gene testing (5% yield in those with macrocephaly >2.5 SD above mean) 3, 1
• Genetic testing should be guided by clinical geneticist evaluation rather than ordering extensive panels without expert input 3

Assessment of Co-occurring Conditions

Adults with ASD have significantly elevated rates of psychiatric comorbidities compared to the general population:

• Depression: 20% vs 7% in general population 7
• Anxiety: 11% vs 5% 7
• Sleep difficulties: 13% vs 5% 7
• Epilepsy: 21% in those with co-occurring intellectual disability 7

Screen systematically for these conditions as part of the diagnostic evaluation, as they require separate treatment interventions 7

Differential Diagnosis Considerations

The heterogeneity of ASD and symptom overlap with other conditions makes differential diagnosis challenging 2:

• Personality disorders: Particularly schizoid, schizotypal, and avoidant personality disorders may present with social difficulties 2
• Anxiety and depression: Can mimic or co-occur with ASD social withdrawal 2
• Obsessive-compulsive disorder: Repetitive behaviors may overlap with restricted/repetitive behaviors in ASD 2
• ADHD: Frequently co-occurs with ASD and shares attentional difficulties 2
• Schizophrenia spectrum disorders: Social deficits and unusual behaviors require careful differentiation 2

The key distinguishing feature is the childhood onset and lifelong persistence of social-communication deficits and restricted/repetitive behaviors in ASD 2

Critical Pitfalls to Avoid

• Do not delay diagnosis due to misconceptions about adult presentation of ASD, particularly in individuals who have developed compensatory strategies or present atypically 1
• Do not rely solely on self-report, as many adults with ASD have limited insight into their social difficulties; collateral history is essential 1
• Do not miss subtle presentations in women and older adults, who are frequently underdiagnosed due to better camouflaging abilities 2
• Do not attribute all symptoms to ASD without screening for treatable co-occurring psychiatric conditions that significantly impact quality of life 7
• Do not order extensive genetic testing without clinical geneticist evaluation first, as a stepwise approach is more cost-effective 3

Prognosis and Long-term Considerations

Adults with ASD face significant challenges:

• 54% unemployment rate in study samples, indicating severely limited occupational perspectives 5
• 2.9 times higher mortality compared to the general population 5
• Many adults, including those with normal IQ, remain significantly disadvantaged regarding employment, social relationships, and quality of life 8

These outcomes underscore the importance of accurate diagnosis to facilitate appropriate accommodations, interventions, and support services 2