What is the diagnosis for a 10-month-old infant with irritability during feeding, multiple vomiting, and a weight below the 3rd percentile, with height and head circumference at the 25th percentile?

Diagnosis: Organic Failure to Thrive

This 10-month-old infant has organic failure to thrive, as evidenced by the combination of specific gastrointestinal symptoms (irritability during feeding and multiple vomiting episodes) with disproportionate growth failure affecting weight alone while height and head circumference remain normal. 1

Key Diagnostic Features Supporting Organic Etiology

Growth Pattern Analysis

• Weight below the 3rd percentile with height and head circumference at the 25th percentile indicates acute malnutrition affecting weight first, which is the critical distinguishing feature of organic failure to thrive 1
• This disproportionate growth failure pattern, where only weight is affected rather than global growth delay, strongly suggests an organic cause rather than nonorganic failure to thrive or chromosomal abnormalities 1

Clinical Symptoms Point to Specific Pathology

• The presence of irritability during feeding combined with multiple vomiting episodes indicates a specific organic gastrointestinal pathology such as gastroesophageal reflux disease (GERD), swallowing dysfunction, or other GI disorders 1
• These are not simple decreased intake symptoms seen in nonorganic failure to thrive, but rather suggest calories are being lost through vomiting or malabsorption 1

Family History Excludes Genetic Causes

• Normal birth history with two healthy older siblings makes chromosomal abnormalities (Option D) highly unlikely 1
• Chromosomal abnormalities typically present with proportionate growth failure affecting weight, height, and head circumference equally, not the isolated weight faltering seen here 1

Why Not Nonorganic Failure to Thrive?

Nonorganic failure to thrive is excluded by the presence of specific GI symptoms rather than simple psychosocial deprivation or inadequate intake. 1 The key distinguishing features include:

• Nonorganic failure to thrive typically presents with decreased intake due to psychosocial factors, economic deprivation, or feeding difficulties without organic pathology 2, 3
• This infant has active symptoms (vomiting, feeding irritability) suggesting an underlying disease process 1
• The absence of psychosocial deprivation indicators further argues against nonorganic etiology 1

Immediate Clinical Approach Required

Essential Investigations

• Gastroenterology referral for evaluation of GERD, swallowing dysfunction, or other GI pathology given the vomiting and feeding irritability 1
• Video swallow study to assess for swallowing dysfunction and aspiration risk 1
• Extended 24-hour esophageal pH monitoring, barium swallow, and gastric scintiscan to evaluate for GERD 1
• Basic laboratory screening: CBC, comprehensive metabolic panel, thyroid function tests (TSH, free T4), and celiac disease screening (tissue transglutaminase antibodies with total IgA) 1

Additional Screening for Specific Organic Causes

• Sweat chloride test for cystic fibrosis (sensitivity 90%, specificity 99%), as pancreatic insufficiency from CF commonly presents with normal birth weight followed by growth failure in early infancy with weight faltering before height faltering 1
• Fecal elastase to assess pancreatic function if pancreatic insufficiency is suspected 1

Monitoring Strategy

• Serial weight measurements every 2-4 weeks initially to track response to interventions 1
• Plot all measurements on WHO growth charts 1

Common Pitfall to Avoid

Do not dismiss this as normal development (Option A) or delay investigation assuming nonorganic causes. The specific symptom complex of vomiting with feeding irritability combined with isolated weight faltering demands immediate organic workup, as early intervention is essential to prevent long-term sequelae from nutritional deficiency and the underlying disease process. 1, 3