A 3-year-old boy is brought to the developmental pediatrics clinic by his mother with concerns about delayed speech and social withdrawal. He was born full-term without complications. The mother reports that he spoke a few words by 18 months but has since lost most of his vocabulary. He does not make eye contact, avoids physical contact, and spends hours lining up toy cars in repetitive patterns. He becomes extremely distressed if his routine is altered. On examination, he shows poor joint attention and does not respond to his name. His developmental screening suggests significant delays across communication and social domains. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Autism Spectrum Disorder with Language Regression ### Key Clinical Features Presented **Key Point:** This case demonstrates the classic presentation of autism spectrum disorder (ASD) with regression, characterized by loss of previously acquired skills (regression in speech and social engagement) combined with persistent deficits in social communication and restricted, repetitive behaviors. ### Diagnostic Criteria Met (DSM-5) | Feature | Present in Case | Diagnostic Significance | |---------|-----------------|------------------------| | Loss of language skills | Yes (words by 18 mo, then lost) | Regression variant of ASD | | Impaired social interaction | Yes (avoids contact, no eye contact) | Core deficit in ASD | | Restricted interests | Yes (lining up cars repetitively) | Restricted/repetitive behavior | | Distress with routine changes | Yes (extreme distress) | Insistence on sameness | | Onset before age 3 | Yes (symptoms evident by 18 mo) | Early childhood onset | | Functional impairment | Yes (across communication & social) | Clinically significant | ### Why This Is Autism Spectrum Disorder (Not Other Diagnoses) **High-Yield:** ASD encompasses a spectrum including cases with early regression (previously called "regressive autism"). The combination of: - Loss of language and social skills - Persistent deficits in social-emotional reciprocity - Restricted, repetitive patterns of behavior - Early onset (before age 3) All meet DSM-5 criteria for ASD Level 2 or 3 (requiring substantial support). **Clinical Pearl:** Approximately 25–30% of children with ASD show regression in language or social skills between 12–24 months. This does NOT change the diagnosis—it is a recognized variant of ASD onset, not a separate entity. ### Regression in ASD: Mechanism ```mermaid flowchart TD A[Typical early development] --> B[12-24 months: Loss of language/social skills]:::urgent B --> C[Concurrent emergence of repetitive behaviors] C --> D[Persistent deficits across domains] D --> E[Diagnosis: ASD with regression variant]:::outcome style A fill:#e8f5e9 style E fill:#bbdefb ``` **Key Point:** Regression in ASD is thought to reflect a plateau in development followed by loss of emerging skills, possibly due to neurobiological factors (abnormal synaptic pruning, immune factors). It is NOT a sign of a degenerative disease or a different disorder. ### Differential Considerations **Warning:** Do NOT confuse ASD with regression with childhood disintegrative disorder (CDD). CDD requires normal development for at least 2 years followed by regression—this child showed early delays and regression by 18 months, fitting ASD better. [cite:DSM-5 Autism Spectrum Disorder Criteria]