What conditions should be considered as differential diagnoses or mimics when evaluating a patient for attention‑deficit/hyperactivity disorder in children, adolescents, and adults?

ADHD Differential Diagnosis

Direct Answer

When evaluating for ADHD, systematically rule out trauma-related disorders (PTSD), mood and anxiety disorders, substance use, sleep disorders, learning disabilities, autism spectrum disorder, and medical conditions (thyroid disease, seizures, sleep apnea) before confirming the diagnosis, as these conditions frequently mimic or coexist with ADHD symptoms. 1, 2

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Mandatory Screening Categories

The American Academy of Pediatrics requires assessment across three domains when evaluating any patient for ADHD 1:

Emotional/Behavioral Conditions

• Depression and anxiety disorders present with hyperarousal and concentration difficulties but lack the pervasive pattern present since before age 12 2
• Post-traumatic stress disorder (PTSD) manifests with impulsivity, hyperarousal, and attention difficulties that closely mimic ADHD, but includes trauma-specific reexperiencing, avoidance, and emotion dysregulation that ADHD lacks 2
• Oppositional defiant disorder and conduct disorders commonly coexist with ADHD in approximately 14% of cases, with rates increasing with age 1, 2
• Reactive attachment disorder presents with inappropriate social responsivity and behavioral dysregulation that can appear impulsive 2

Developmental Conditions

• Learning disabilities and language disorders commonly present with inattention and behavioral dysregulation that appears impulsive 1, 2
• Autism spectrum disorder (ASD) requires differentiation based on core social-communication deficits: failure to respond to name at 12 months (86% specificity for ASD), deficits in joint attention initiation, qualitatively impaired eye contact, and repetitive behaviors serving self-regulatory functions rather than being driven by impulsivity 3
• Developmental coordination disorder may present with motor restlessness misinterpreted as hyperactivity 2

Physical/Medical Conditions

• Sleep disorders, including sleep apnea, produce daytime hyperactivity, inattention, and impulsive behavior that resolves with treatment of the underlying sleep problem 1, 2
• Tic disorders can present with motor restlessness and impulsive movements 1, 2
• Seizure disorders, particularly absence seizures, can mimic inattention 2
• Thyroid disease has symptoms similar to ADHD and must be excluded 4

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Age-Specific Considerations

Adolescents and Adults

• Substance use disorders (particularly marijuana) produce effects mimicking ADHD symptoms including impulsivity and inattention 2, 5
• Adolescents may feign ADHD symptoms to obtain stimulant medications for performance enhancement 2
• Mood disorders, personality disorders, and impulse control disorders have substantial symptom overlap with adult ADHD and must be systematically evaluated 5, 6
• Medications including steroids, antihistamines, anticonvulsants, caffeine, and nicotine can have adverse effects that mimic ADHD symptoms 4

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Critical Diagnostic Algorithm

Step 1: Verify DSM Criteria Before Considering Alternatives 1, 2

• Document at least 6 symptoms (5 for adolescents ≥17 years) present for at least 6 months
• Confirm symptom onset before age 12 with documented or reliably reported manifestations from childhood
• Obtain information from at least two teachers plus parents/guardians to document cross-setting impairment in multiple major settings

Step 2: Rule Out Alternative Causes 1, 2

• Screen for trauma history and PTSD symptoms (reexperiencing, avoidance, emotion dysregulation)
• Assess for mood and anxiety disorders with timeline establishing whether symptoms preceded ADHD presentation
• Evaluate for substance use in adolescents and adults
• Screen for sleep disorders with detailed sleep history
• Consider medical conditions (thyroid, seizures) with appropriate laboratory/diagnostic testing

Step 3: Screen for Coexisting Conditions 1, 2

• Even when ADHD criteria are met, systematically assess for anxiety (present in 14% of ADHD cases), depression, learning disabilities, language disorders, and tic disorders
• The majority of children presenting with ADHD-like symptoms meet criteria for another mental disorder, making comorbidity screening essential rather than optional 2

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Common Diagnostic Pitfalls to Avoid

• Failing to obtain information from multiple settings before concluding ADHD criteria are met leads to misdiagnosis 2
• Assigning an ADHD diagnosis when symptoms are better explained by trauma, substance use, or other psychiatric conditions results in inappropriate treatment 2
• Not establishing that symptoms were present before age 12 in adolescents leads to misdiagnosis of conditions that emerged later 2, 5
• Diagnostic overshadowing, where comorbid conditions are missed due to a more noticeable condition being present 3
• Relying solely on parent or teacher reports without corroborating information from multiple sources produces diagnostic errors 2
• Empiric diagnostic trials of stimulant medication that produce a behavioral response do not distinguish between children with and without ADHD 7

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When Subspecialist Referral Is Indicated

Refer to child psychiatrists, developmental-behavioral pediatricians, or child psychologists when 1, 5:

• Diagnostic uncertainty exists due to complex comorbidities
• Severe mood or anxiety disorders are present
• Active substance use disorder requires specialized addiction treatment before ADHD treatment
• Severe mood instability suggests bipolar disorder requiring mood stabilization first