Step 1: Understanding the Concept:
This case is testing whether you can pick out the classic triad of autism spectrum disorder from a short clinical picture.
Step 2: Key Approach:
List the three domains that must all be present for autism: social interaction problems, communication problems, and repetitive or restricted behavior with resistance to change. Then check the case against each domain.
Step 3: Detailed Explanation:
Social domain: the child does not mix with people, a clear withdrawal from social contact.
Communication domain: he does not communicate well, showing a language or expressive deficit.
Behavior domain: he has limited interests and becomes wildly agitated if disturbed, both textbook signs of rigid, repetitive behavior and an intolerance to change.
All three domains are present, plus a background of birth asphyxia, a recognized risk factor for the condition.
Histrionic personality does not explain a communication deficit. ADHD does not explain social withdrawal or rigid interests as its core feature. Schizophrenia would need hallucinations or delusions, which are absent, and is very uncommon at age 6.
Step 4: Final Answer:
Since all three core domains of autism are satisfied, the diagnosis is autistic disorder.