A 3-year-old boy is brought to the developmental paediatrics clinic by his mother with concerns about delayed speech and social withdrawal. She reports that he spoke a few words at 18 months but has regressed and now uses only single words inconsistently. He does not make eye contact, avoids physical contact, and spends hours lining up toy cars in repetitive patterns. He becomes distressed if his routine is altered. On examination, he shows poor joint attention and does not respond to his name. He has normal hearing on audiometry and normal developmental milestones for gross motor skills. What is the most likely diagnosis?

Explanation

## Diagnosis: Autism Spectrum Disorder ### Clinical Features Present in This Case **Key Point:** This child demonstrates the core diagnostic criteria for Autism Spectrum Disorder (ASD) per **DSM-5**: 1. **Social communication deficits** — poor eye contact, lack of joint attention, no response to name, social withdrawal, avoidance of physical contact 2. **Restricted/repetitive behaviours (RRBs)** — lining up toys in repetitive patterns, distress with routine changes 3. **Early onset** — symptoms evident before age 3 years ### DSM-5 Criteria for ASD (ICD-11: 6A02) The child meets criteria across both mandatory domains: | Domain | Criterion | Present in Case | | --- | --- | --- | | **Social Communication** | Deficits in social-emotional reciprocity | Avoids contact, no joint attention | | **Social Communication** | Deficits in nonverbal communication | Poor eye contact | | **Social Communication** | Deficits in developing/maintaining relationships | Social withdrawal | | **Restricted Behaviour** | Stereotyped/repetitive motor movements or use of objects | Lining up toys | | **Restricted Behaviour** | Insistence on sameness, rigid routines | Distress with routine changes | | **Onset** | Symptoms present in early developmental period | Age 3 years | **High-Yield:** The presence of **language regression** (loss of previously acquired words) is a recognised red flag for ASD and does NOT exclude the diagnosis — it may indicate a more severe phenotype. Regression in ASD typically occurs before 24 months, distinguishing it from Childhood Disintegrative Disorder (CDD). ### Why Not the Other Options? **Clinical Pearl:** - **Option A — Specific Language Impairment (SLI):** SLI involves isolated language delay without social deficits or RRBs. This child has prominent social withdrawal, poor joint attention, and repetitive behaviours — ruling out SLI. - **Option B — Childhood Disintegrative Disorder (CDD / Heller's syndrome):** CDD (now subsumed under ASD in DSM-5) classically requires **at least 2 years of entirely normal development** followed by marked regression in multiple domains (language, social skills, bowel/bladder control, motor skills). This child's regression began at ~18 months — before the 2-year threshold — making ASD the more appropriate diagnosis. CDD regression is also typically more catastrophic and involves multiple developmental domains simultaneously. - **Option D — Intellectual Disability with Speech Delay:** ID alone does not explain the specific social communication deficits (poor joint attention, no response to name, avoidance of eye contact) or the restricted/repetitive behaviours. Normal gross motor milestones also argue against global developmental delay as the primary diagnosis. **Normal hearing on audiometry** rules out hearing impairment as a cause of speech delay, further supporting ASD. ### Severity Classification Under DSM-5, this child's features (language regression, marked social withdrawal, significant RRBs) suggest **Level 2 or Level 3 ASD** (requiring substantial to very substantial support). **Mnemonic: SOCIAL-RRB** — **S**ocial deficits, **O**bsessive routines, **C**ommunication problems, **I**nsistence on sameness, **A**bnormal eye contact, **L**imited joint attention; **R**epetitive **R**igid **B**ehaviours. > *Reference: DSM-5 (APA, 2013), Section on Neurodevelopmental Disorders; Nelson's Textbook of Pediatrics, 21st ed., Chapter on Autism Spectrum Disorder.*