Clinical Scenario:
A 3-year-old boy with Down syndrome is brought to the pediatric clinic with a history of severe constipation since birth. His parents report that he passed meconium more than 48 hours after delivery. He has required repeated enemas and laxatives since infancy. Over the past 2 days, he has developed progressive abdominal distension and bilious vomiting.
On examination:
- Weight is below the 5th percentile.
- Abdomen is markedly distended.
- The rectum is empty on digital rectal examination, followed by explosive passage of stool and flatus after withdrawal of the examining finger.
What is the most likely diagnosis?
A. Celiac disease
B. Chronic intestinal pseudo-obstruction
C. Functional constipation
D. Hirschsprung disease
E. Hypothyroidism
Correct answer & Explanation:
Correct Answer: D. Hirschsprung disease
Explanation:
This 3-year-old boy with Down syndrome has classic features suggestive of Hirschsprung disease (congenital aganglionic megacolon)
Hirschsprung disease should be suspected in a child with constipation beginning in infancy, delayed passage of meconium, abdominal distension, and obstructive symptoms. Digital rectal examination may reveal an empty rectal vault followed by explosive evacuation of stool and flatus. However, the diagnosis is confirmed by rectal biopsy demonstrating absence of ganglion cells.
Association with Down syndrome:
Children with Down syndrome have a significantly increased risk of Hirschsprung disease due to abnormal migration of neural crest cells leading to absence of ganglion cells in the distal colon.
Why other options are incorrect:
A. Celiac disease
- Can cause abdominal distension, poor growth, and constipation in some children, but does not cause delayed meconium passage or explosive stool after rectal examination.
B. Chronic intestinal pseudo-obstruction
- Causes symptoms of bowel obstruction without a mechanical blockage, but typically presents with vomiting, distension, and feeding intolerance rather than delayed meconium with classic rectal findings.
C. Functional constipation
- Usually begins after infancy, often associated with stool withholding behavior, and children typically have a normal rectal examination with fecal impaction. Delayed meconium passage suggests an organic cause.
E. Hypothyroidism
- Can cause constipation and poor growth but does not explain delayed meconium passage and the characteristic explosive stool after rectal examination.
Exam Pearl:
Down syndrome + delayed meconium passage + constipation from infancy + empty rectum with explosive stool/flatus → strongly suspect Hirschsprung disease; confirm with rectal biopsy.
References
- Kyrklund K, Pakarinen MP, Rintala RJ, Koivusalo A, editors. ERNICA guidelines for the management of rectosigmoid Hirschsprung’s disease. Orphanet J Rare Dis. 2020;15:164.
- Updated European Reference Network for rare Inherited and Congenital Digestive and Gastrointestinal Anomalies guidelines for the management of rectosigmoid Hirschsprung’s disease. 2025.
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