A 3-year-old boy is brought to the child psychiatry clinic by his parents with concerns about delayed speech, poor eye contact, and repetitive hand movements. The child shows minimal interest in peer interaction and has restricted interests in spinning objects. Which investigation is most appropriate for confirming the diagnosis of Autism Spectrum Disorder?

Explanation

## Diagnostic Confirmation in Autism Spectrum Disorder **Key Point:** The Autism Diagnostic Observation Schedule (ADOS-2) is the gold-standard, semi-structured observational assessment tool for confirming ASD across all age groups and developmental levels. ### Why ADOS-2 is the Investigation of Choice The ADOS-2 is a standardized, play-based assessment that: - Directly observes social communication, reciprocal interaction, and restricted/repetitive behaviors - Provides domain-specific scores with established cutoffs for ASD diagnosis - Is validated across ages 12 months to adulthood - Yields high sensitivity (95%) and specificity (89%) for ASD diagnosis - Complements the Autism Diagnostic Interview-Revised (ADI-R), which captures developmental history ### Diagnostic Algorithm for ASD ```mermaid flowchart TD A[Suspected ASD based on developmental screening]:::outcome --> B[Detailed developmental history + parental interview]:::action B --> C[ADOS-2: Standardized observation]:::action C --> D[ADI-R: Structured parental interview]:::action D --> E{Criteria met for ASD?}:::decision E -->|Yes| F[Confirm ASD diagnosis]:::outcome E -->|No| G[Consider alternative diagnoses]:::outcome B --> H[Rule out medical/genetic causes]:::action H --> I[Hearing assessment, metabolic screening if indicated]:::action ``` **High-Yield:** ADOS-2 is the only investigation among the options that directly assesses the core diagnostic features of ASD (social-communication deficits and restricted/repetitive behaviors) in a standardized, validated manner. ### Differential Role of Other Investigations | Investigation | Role in ASD Evaluation | When Indicated | |---|---|---| | **EEG** | Not diagnostic for ASD; used only if seizures suspected | Comorbid seizure disorder (25–30% of ASD) | | **MRI brain** | No specific diagnostic finding for ASD; used to rule out structural abnormalities | Focal neurological signs, regression, atypical presentation | | **Metabolic screening** | Detects rare genetic/metabolic causes (e.g., fragile X, metabolic disorders) | Family history, dysmorphic features, developmental regression | **Clinical Pearl:** While structural neuroimaging and metabolic screening may be part of the *workup* to exclude secondary causes, they are not diagnostic for ASD itself. The diagnosis of ASD is behavioral and requires standardized observational assessment.