What are the differential diagnoses to consider when evaluating a patient for attention‑deficit/hyperactivity disorder?

ADHD Differential Diagnosis

When evaluating a patient for ADHD, you must systematically rule out trauma/PTSD, substance use disorders, mood and anxiety disorders, sleep disorders, learning disabilities, and medical conditions—particularly because the majority of patients presenting with ADHD-like symptoms actually meet criteria for another mental disorder. 1

Mandatory Screening Framework

The American Academy of Pediatrics requires evaluation across three domains before confirming ADHD: emotional/behavioral conditions, developmental conditions, and physical/medical conditions. 2, 1

Emotional and Behavioral Conditions

Trauma and Stress-Related Disorders

• Post-traumatic stress disorder (PTSD) and complex PTSD manifest with impulsivity, hyperarousal, and attention difficulties that closely mimic ADHD symptoms. 1
• PTSD includes trauma-specific reexperiencing, avoidance, and emotion dysregulation that ADHD lacks—verify trauma history and temporal relationship between trauma exposure and symptom onset. 1
• Reactive attachment disorder presents with inappropriate social responsivity and behavioral dysregulation appearing impulsive. 1

Mood Disorders

• Depression occurs in approximately 9% of ADHD patients and can mimic inattention through psychomotor slowing and concentration difficulties. 3, 4
• Bipolar disorder presents with episodic mood changes, racing thoughts during manic phases, and distractibility that follows a distinct temporal pattern tied to mood episodes—not the pervasive pattern present since before age 12 required for ADHD. 3, 4
• Optimize treatment of mood disorders before confirming ADHD diagnosis, as residual attentional symptoms may resolve with adequate mood stabilization. 3, 4

Anxiety Disorders

• Anxiety disorders are present in approximately 14% of children with ADHD, with rates increasing with age. 1
• Anxiety-related hyperarousal and worry-driven distractibility can appear identical to ADHD but lack the pervasive developmental pattern. 1

Substance Use Disorders

• Marijuana use in adolescents and adults produces impulsivity and inattention indistinguishable from ADHD symptoms. 1, 3
• Stimulant use, alcohol abuse, and other substances can mimic or exacerbate ADHD presentations. 3, 5
• Some adolescents intentionally feign ADHD symptoms to obtain stimulant medications for performance enhancement. 1
• Critical step: Reassess after sustained abstinence from substance use before finalizing ADHD diagnosis. 3

Personality Disorders

• Borderline and antisocial personality disorders present with impulsivity and emotional dysregulation that overlap with ADHD but include distinct interpersonal patterns and identity disturbance. 3, 4

Developmental and Learning Conditions

Learning Disabilities

• Learning disabilities and language disorders commonly present with inattention and behavioral dysregulation appearing impulsive. 1, 3
• These conditions are domain-specific (reading, writing, mathematics) rather than pervasive across all settings. 4
• Screen adults for previously undiagnosed learning disabilities, as these persist into adulthood and affect functional outcomes. 3

Autism Spectrum Disorders

• Autism spectrum disorders manifest with impulsive behaviors, difficulty with behavioral regulation, and atypical social responsiveness that can mimic ADHD. 1

Physical and Medical Conditions

Sleep Disorders

• Sleep apnea produces daytime hyperactivity, inattention, and impulsive behavior that resolves with CPAP treatment. 1, 4
• Sleep deprivation from any cause can mimic ADHD symptoms. 6
• Obtain detailed sleep history including snoring, witnessed apneas, daytime somnolence, and sleep quality. 1

Neurological Conditions

• Seizure disorders, particularly absence seizures, mimic inattention through brief lapses in consciousness. 1, 6
• Tic disorders present with motor restlessness and impulsive movements misinterpreted as hyperactivity. 1
• Post-concussion states produce attention deficits and behavioral changes. 6

Endocrine and Metabolic Disorders

• Thyroid dysfunction (both hyper- and hypothyroidism) produces concentration difficulties, restlessness or lethargy, and mood changes. 4, 7
• Diabetes with poor glycemic control causes cognitive slowing and inattention. 6
• Iron deficiency and anemia result in fatigue and impaired concentration. 6

Other Medical Conditions

• Inflammatory bowel disease can present with attention difficulties. 6
• Disordered breathing conditions beyond sleep apnea affect cognitive function. 6

Critical Diagnostic Algorithm

Step 1: Verify DSM-5 ADHD Criteria

• Document at least 6 symptoms (5 for adolescents ≥17 years and adults) persisting for ≥6 months. 1, 3
• Confirm symptom onset before age 12 through patient recall, collateral informants (parents, siblings), old report cards, or school records. 1, 3, 4
• Obtain information from at least two teachers (or equivalent school/work personnel) plus parents/guardians or partners to demonstrate cross-setting impairment. 1, 3
• Verify functional impairment in at least 2 independent settings (work, home, social relationships, academic). 3, 4

Step 2: Rule Out Alternative Causes

• Conduct trauma screening: Assess for PTSD symptoms including reexperiencing, avoidance, and emotional dysregulation. 1, 4
• Evaluate substance use: Obtain detailed substance use history and consider urine drug screening before confirming diagnosis. 3, 4
• Assess mood and anxiety: Determine whether these symptoms predate, co-occur with, or better explain attentional difficulties. 1, 3
• Perform sleep evaluation: Screen for sleep apnea, insomnia, and other sleep disorders. 1, 4
• Order appropriate testing: Consider thyroid function tests, complete blood count, and other laboratory studies based on clinical presentation. 4, 6, 7

Step 3: Screen for Comorbidities

Even after meeting ADHD criteria, systematically assess for:

• Oppositional defiant disorder and conduct disorder (present in approximately 14% of cases). 1
• Anxiety disorders (14% comorbidity rate). 1
• Depression (9% comorbidity rate). 3
• Learning disabilities and language disorders. 1, 3
• Tic disorders. 1

Common Diagnostic Pitfalls

Failing to Establish Childhood Onset

• Not verifying that symptoms were present before age 12 leads to misdiagnosing conditions such as adult-onset depression, substance-induced attentional problems, or personality disorders. 1, 4

Inadequate Cross-Setting Documentation

• Relying solely on self-report or single-informant data without corroborating information from multiple sources produces diagnostic errors. 1, 3
• Adults often minimize symptoms, making collateral information essential. 3, 8

Misattributing Symptoms

• Assigning ADHD diagnosis when symptoms are better explained by trauma, substance use, mood disorders, or anxiety results in inappropriate treatment and missed opportunities to address the true underlying cause. 1, 4

Using Rating Scales Alone

• Rating scales (Adult ADHD Self-Report Scale, Conners scales) facilitate screening but do not diagnose ADHD by themselves—comprehensive clinical interview is mandatory. 3, 5, 9

Missing Active Substance Use

• Failing to obtain urine drug screens or detailed substance use history before confirming ADHD diagnosis leads to misdiagnosis. 4

When to Refer

Refer to child psychiatrist, developmental-behavioral pediatrician, or child psychologist when:

• Diagnostic uncertainty exists due to complex comorbidities or atypical presentations. 2, 3
• Severe mood or anxiety disorders require specialized management. 2
• Active substance use disorder complicates assessment. 3
• Treatment-resistant ADHD or suspected personality disorder is present. 3

Special Considerations for Children Under 4 Years

There is insufficient evidence to recommend ADHD diagnosis or treatment for children younger than 4 years. 2

• When ADHD-like symptoms in children younger than 4 years cause substantial impairment, consider referral for parent training in behavior management, which does not require a formal diagnosis. 2