A 7-year-old boy is brought to the child psychiatry clinic by his mother with complaints of inattention, impulsivity, and hyperactivity at school and home for the past 18 months. The teacher reports difficulty in sustained attention during classroom activities and frequent interruption of peers. Physical examination and basic metabolic investigations are unremarkable. Which of the following is the investigation of choice to confirm the diagnosis of ADHD?

Explanation

## Investigation of Choice for ADHD Diagnosis **Key Point:** The Continuous Performance Test (CPT) is the gold-standard objective neuropsychological investigation for ADHD. It measures sustained attention, impulse control, and reaction time variability — the core deficits in ADHD. ### Why CPT is the Investigation of Choice **High-Yield:** CPT is a computerized task that requires the child to respond to target stimuli while ignoring non-target stimuli over an extended period. It provides quantitative measures of: - **Omission errors** (missed targets) → reflects inattention - **Commission errors** (false alarms) → reflects impulsivity - **Reaction time variability** → reflects executive dysfunction **Clinical Pearl:** ADHD diagnosis remains primarily clinical (based on DSM-5 or ICD-11 criteria), but CPT serves as an objective, validated adjunct investigation to support the diagnosis, especially when clinical presentation is ambiguous or comorbidities are suspected. ### Role of Other Investigations | Investigation | Role in ADHD | Why Not First-Line | |---|---|---| | **EEG** | May show nonspecific abnormalities; not diagnostic | Lacks specificity; abnormal EEG does not confirm ADHD | | **Functional MRI** | Research tool; shows prefrontal/striatal hypoactivity | Expensive, not clinically available, not part of diagnostic algorithm | | **Serum lead levels** | Screen for lead toxicity (mimics ADHD) | Indicated only if environmental exposure suspected; not diagnostic for ADHD | **Tip:** Always rule out secondary causes (lead toxicity, thyroid disorder, sleep apnea, hearing loss) with basic screening before attributing symptoms to ADHD. ### Diagnostic Algorithm ```mermaid flowchart TD A[Child with suspected ADHD]:::outcome --> B[Detailed history from parents & teachers]:::action B --> C[Clinical examination & rule out mimics]:::action C --> D{Meets DSM-5 criteria?}:::decision D -->|Yes| E[CPT or IQ/neuropsych testing]:::action D -->|No| F[Reassess or investigate alternatives]:::action E --> G[Confirm ADHD diagnosis]:::outcome F --> H[Consider other diagnoses]:::outcome ``` [cite:DSM-5 ADHD Criteria; Barkley RA, Child ADHD Assessment]