How is autism diagnosed in adults with Attention Deficit Hyperactivity Disorder (ADHD)?

Diagnosing Autism in Adults with ADHD

Adults with ADHD should be systematically screened for autism spectrum disorder using the Autism Diagnostic Observation Schedule-2 (ADOS-2) Module 4 when they present with social relationship difficulties, repetitive behaviors, or more severe functional impairment than expected from ADHD alone. 1, 2

Why This Matters Clinically

Approximately 50% of individuals with autism also meet full diagnostic criteria for ADHD, and the overlap creates significantly worse outcomes—including more severe deficits in social processing, adaptive functioning, and executive control—than either condition alone. 1, 3 Adults with ADHD frequently exhibit substantial autistic symptoms that fall between those with diagnosed autism and neurotypical individuals, making systematic screening essential rather than optional. 2

Structured Diagnostic Protocol

Initial Screening Approach

• Begin with the Adult ADHD Self-Report Scale (ASRS-V1.1) Part A to confirm ADHD symptoms (positive screen = 4 or more items marked "often" or "very often" out of 6 questions). 4
• Simultaneously screen for autism symptoms using the Autism Spectrum Quotient, specifically assessing social relationship deficits and repetitive or unusual behaviors. 1, 2
• Obtain collateral information from spouse, partner, parent, or close friend, as adults with ADHD often underestimate their symptom severity and functional impairment. 4

Comprehensive Diagnostic Evaluation

• Administer the ADOS-2 Module 4 (the adult module) when autism symptoms are suspected, as this provides standardized observation of social communication and restricted/repetitive behaviors. 2
• Confirm all DSM-5 criteria for both disorders: ADHD requires at least 5 symptoms of inattention and/or hyperactivity-impulsivity present for ≥6 months, symptom onset before age 12, and symptoms present in ≥2 settings with functional impairment. 4, 1
• Document childhood history through parent or sibling interviews, as retrospective recall of childhood symptoms before age 12 is required for ADHD diagnosis and helps distinguish primary ADHD from secondary attentional difficulties in autism. 1, 5

Critical Diagnostic Distinctions

• Avoid confusing secondary attentional difficulties in autism with primary ADHD—individuals with autism may appear inattentive due to social disengagement or perseverative interests rather than true attention deficit. 1
• Do not assume hyperactivity in autism always represents ADHD—motor stereotypies and stimming behaviors can mimic hyperactivity but serve different functions. 1
• Item-level analysis shows more similarities than differences between the disorders, with differences being of degree rather than quality, making careful clinical judgment essential. 2

Mandatory Comorbidity Assessment

Screen systematically for additional conditions that worsen outcomes when comorbid with ADHD and autism: 6, 7, 1

• Mood disorders: Depression and anxiety (present in approximately 14% and 9% of ADHD cases respectively)
• Substance use disorders: Particularly critical in adults, as untreated ADHD increases risk
• Learning disabilities and language disorders
• Sleep disorders: Common in both ADHD and autism
• Obsessive-compulsive disorder: Overlaps with autism's restricted/repetitive behaviors

Clinical Interview Focus Areas

The clinician-administered interview remains the cornerstone of adult diagnosis. 5 Document:

• Current functional impairment in at least two realms (home, work, social interactions) for ADHD diagnosis
• Social communication deficits across contexts for autism diagnosis
• Childhood symptom onset before age 12 through collateral sources
• Poor psychosocial outcomes (relationship failures, job instability, legal problems) that often indicate unrecognized, untreated disorder manifestations 5

Common Diagnostic Pitfalls

• Failing to assess full autism symptoms in adults presenting with ADHD—recent research demonstrates this is essential, not optional. 2
• Relying solely on self-report—adults with ADHD underestimate their impairment, making collateral information mandatory. 4
• Missing the comorbid diagnosis—individuals with both conditions are more severely impaired and require different treatment approaches than ADHD alone. 1, 3
• Treating in isolation—untreated comorbidities significantly worsen outcomes and increase risk for early death, suicide, psychiatric complications, and functional decline. 6, 7

Treatment Implications of Comorbid Diagnosis

When both ADHD and autism are confirmed: 1, 3

• Stimulant medications remain first-line but require lower doses and slower titration than ADHD alone
• Response rates are lower than primary ADHD (effects not as great as treating ADHD without autism)
• Side effects are more common and less well-tolerated in the autism population
• Alternative agents (alpha-agonists like guanfacine, atomoxetine) may be better tolerated
• Behavioral interventions must address both ADHD symptoms and autism-specific social communication deficits