Interstitial lung disease in children — short-answer question

Part A — Definition, framing and mechanism (10 marks)

a) Define the chILD syndrome and explain why it applies here (4 marks)

Children's interstitial lung disease, or chILD, is a heterogeneous group of rare diffuse lung disorders that thicken and disrupt the alveolar-interstitial region and impair gas exchange. The chILD syndrome is the practical entry point: diffuse lung disease with at least three of four features — respiratory symptoms, respiratory signs, hypoxaemia, and diffuse abnormalities on imaging — once the common causes are excluded. This infant has persistent respiratory symptoms, tachypnoea and diffuse crackles, hypoxaemia at rest and during feeds, and diffuse radiographic change, so he meets the chILD syndrome and needs a structured diffuse-lung-disease evaluation rather than further empirical treatment for infection. ^{[1] [4]}

b) Outline how you would classify chILD and where this infant fits (4 marks)

The most useful classification splits chILD by age. An infancy-predominant group contains diffuse developmental disorders, growth abnormalities with alveolar simplification, the genetic surfactant dysfunction disorders (surfactant protein B, surfactant protein C, ABCA3, NKX2-1), and specific conditions of unknown cause such as neuroendocrine cell hyperplasia of infancy and pulmonary interstitial glycogenosis. A separate older-child group is organised by host and exposure and resembles adult interstitial lung disease. This infant sits firmly in the infancy-predominant group, and the leading possibilities are a surfactant dysfunction disorder and neuroendocrine cell hyperplasia of infancy. ^{[2] [1]}

c) Explain the two paradigm mechanisms in infancy (2 marks)

The surfactant dysfunction disorders arise when the type II pneumocyte cannot make or process surfactant because of a gene defect, causing alveolar collapse and interstitial thickening; surfactant protein B and ABCA3 defects tend to be lethal in the newborn, while surfactant protein C disease is chronic and variable. Neuroendocrine cell hyperplasia of infancy works differently, with increased bombesin-positive airway neuroendocrine cells but near-normal lung architecture, which is why it behaves far more benignly. ^{[2] [3]}