Differential Diagnosis for a 4-Day-Old Full-Term Infant with Labored Breathing and 16% Body Weight Loss

• Single Most Likely Diagnosis
  • Dehydration: This is the most likely diagnosis given the significant weight loss of 16% in a short period, which is a common cause of labored breathing in neonates due to metabolic acidosis and possible electrolyte imbalances.
• Other Likely Diagnoses
  • Respiratory infection (e.g., pneumonia): Infections can cause labored breathing and failure to thrive, leading to weight loss.
  • Congenital heart disease: Although less common, it can present with respiratory distress and failure to thrive.
  • Transient tachypnea of the newborn (TTN): Although typically seen immediately after birth, some cases can persist.
• Do Not Miss Diagnoses
  • Congenital diaphragmatic hernia: A life-threatening condition that requires immediate surgical intervention.
  • Necrotizing enterocolitis: Although more common in preterm infants, it can occur in full-term babies and is a medical emergency.
  • Sepsis: Infection can quickly escalate and become life-threatening, making prompt diagnosis and treatment crucial.
• Rare Diagnoses
  • Metabolic disorders (e.g., congenital adrenal hyperplasia): These can present with failure to thrive, weight loss, and respiratory distress due to metabolic crises.
  • Cystic fibrosis: Although rare to present this early, it can cause respiratory symptoms and failure to thrive.
  • Pulmonary lymphangiectasia: A rare condition that can cause respiratory distress in neonates.