Diagnosing Autism Spectrum Disorder in Adults
The diagnosis of autism spectrum disorder (ASD) in adults requires a comprehensive evaluation by professionals trained in ASD diagnosis, using standardized assessment tools and objective criteria based on DSM-5 guidelines.
Diagnostic Process
Initial Assessment
- Screening should include inquiries about core ASD symptoms, including social relatedness and repetitive or unusual behaviors 1
- A thorough psychiatric assessment should be conducted, including interviews with the individual and family members when possible, and review of past records and developmental history 1, 2
- Assessment should focus on the two core domains of ASD according to DSM-5:
- Persistent deficits in social communication and social interaction
- Restricted, repetitive patterns of behavior, interests, or activities 3
Comprehensive Evaluation
- Confirmation of ASD diagnosis should be made by a professional trained in diagnosing autism using objective criteria and standardized tools 1, 2
- A multidisciplinary team approach is recommended, which may include psychologists, psychiatrists, speech-language pathologists, and occupational therapists 2, 4
- Sensory screening, including a complete audiogram, should be performed to rule out hearing loss that could mimic ASD symptoms 1
- Cognitive testing should be included to assess intellectual functioning 1
Diagnostic Tools and Measures
Standardized Assessment Instruments
- The Autism Diagnostic Observation Schedule-Second Edition (ADOS-2) is considered a gold standard observational measure with sensitivity of 91% and specificity of 76% 4
- The Autism Diagnostic Interview-Revised (ADI-R) is a comprehensive caregiver interview with sensitivity of 80% and specificity of 72% 4
- Self-report measures like the Autism Spectrum Quotient (AQ) and the Ritvo Autism Asperger's Diagnostic Scale-Revised (RAADS-R) may be used but should not be relied upon alone due to limited diagnostic validity in adults 5
Important Considerations
- Standard diagnostic measures may miss subtle or atypical presentations, particularly in underdiagnosed groups like women and older adults 3
- Clinicians should not rely solely on self-report measures or the ADOS when diagnosing adults on the spectrum 5
- Multiple measures (interviews and questionnaires) should be used together when diagnosing ASD in adulthood 5
Differential Diagnosis
- Assessment must carefully differentiate ASD from conditions with overlapping symptoms 3:
- Personality disorders (particularly schizoid, schizotypal, and avoidant)
- Anxiety disorders
- Depression
- Obsessive-compulsive disorder
- Attention-deficit/hyperactivity disorder
- Schizophrenia
Medical Evaluation
Genetic Testing
- Consider genetic testing as part of the evaluation 1, 2:
- High-resolution chromosomal analysis
- DNA testing for Fragile X syndrome
- Chromosomal microarray (comparative genomic hybridization)
- MECP2 gene testing (females only)
- PTEN gene testing (if head circumference is 2.5 SD greater than mean)
Additional Medical Assessment
- Evaluate for common co-occurring conditions, as individuals with ASD have higher rates of 4:
- Depression (20% vs 7% in general population)
- Anxiety (11% vs 5%)
- Sleep difficulties (13% vs 5%)
- Epilepsy (21% with co-occurring intellectual disability vs 0.8%)
Common Pitfalls to Avoid
- Delaying diagnosis due to misconceptions about adult presentation of ASD 2
- Relying solely on self-report measures which have poor to fair sensitivity and specificity in adults 5
- Failing to consider gender differences in presentation, which may lead to underdiagnosis in women 3
- Not differentiating ASD from psychiatric conditions with overlapping symptoms 3
- Focusing only on current symptoms without establishing developmental history and childhood onset 3