Diagnosis: Incomplete Relaxation of Lower Esophageal Sphincter (Answer B)
The most likely underlying abnormality in this 6-month-old infant is incomplete relaxation of the lower esophageal sphincter (LES), which is the primary pathophysiologic mechanism causing gastroesophageal reflux disease (GERD) with its associated complications of recurrent aspiration and Sandifer syndrome.
Pathophysiology of the Clinical Presentation
The clinical triad presented—frequent vomiting after feeding, recurrent chest infections, and tonic neck muscle posturing—is pathognomonic for GERD with complications:
Transient relaxations of the lower esophageal sphincter are the predominant mechanism causing GERD in infants, permitting gastric contents to enter the esophagus independent of swallowing 1, 2.
Recurrent chest infections result from repeated pulmonary aspiration of gastric fluid, which is one of the most frequent complications of recurrent GER in childhood 3. The reflux of gastric contents can cause aspiration pneumonitis and recurrent bronchitis or pneumonia 3, 4.
Tonic neck muscle posturing represents Sandifer syndrome, which is an extraesophageal manifestation of GERD in infants characterized by abnormal posturing (back arching and neck extension) that represents the non-verbal equivalent of heartburn 2. This irritability coupled with back arching is thought to be the infant's response to esophageal pain 2.
Why Not the Other Options
Option A (Upper esophageal sphincter): Incomplete relaxation of the upper esophageal sphincter would cause dysphagia and choking with initiation of swallowing, not post-feeding vomiting with aspiration 3. This is not the typical presentation described.
Option C (Hypertrophy of esophageal muscles): This would suggest achalasia or esophageal motility disorders, which are extremely rare in 6-month-old infants and would present with progressive dysphagia to both solids and liquids, not the pattern of post-feeding vomiting with aspiration 3, 5.
Clinical Significance and Management Implications
This infant has GERD disease (not simple physiologic GER) because troublesome symptoms and complications are present 1:
Weight loss or failure to thrive should be assessed, as this distinguishes GERD disease from benign reflux and warrants aggressive intervention 6.
Recurrent respiratory symptoms from aspiration represent life-threatening complications that may require escalation beyond conservative management 2, 3.
The American Academy of Pediatrics emphasizes that infants with recurrent regurgitation and troublesome symptoms require different management than "happy spitters" with physiologic GER 1.
Diagnostic and Treatment Approach
Initial management includes lifestyle modifications, dietary changes (consider cow's milk protein elimination as 42-58% of infants with GERD have concurrent milk protein allergy), and parental education 2.
If conservative measures fail after 2-4 weeks, empirical PPI trial for 2 weeks is recommended, with continuation for 8-12 weeks if symptoms improve 1, 6.
Specialist referral to pediatric gastroenterology is warranted if treatment fails or if life-threatening complications persist 1, 2.
Surgical fundoplication is reserved for selective infants who do not respond to medical therapy and have life-threatening complications of GERD 2.
Critical Pitfall to Avoid
Do not confuse this presentation with pyloric stenosis, which presents with non-bilious projectile vomiting in infants 2 weeks to 3 months old, without respiratory symptoms or abnormal posturing 7. The presence of recurrent chest infections and Sandifer syndrome clearly points to GERD with aspiration, not pyloric stenosis.