20th February 2025

Acute interstitial pneumonia (AIP)

This form of IIP has an acute onset and is characterised by idiopathic, rapidly developing diffuse alveolar damage, possibly leading to fulminant respiratory failure.

It is often preceded by a viral-like illness. Examination reveals widespread crepitations. Profound hypoxia and respiratory failure are often present.

Investigations include:

• CXR: shows a non-specific pattern, often similar to ARDS with bilateral air-space diffuse opacities. This can progress to reticular shadowing and ground-glass appearance, often sparing the hila, heart borders and costophrenic angles
• HRCT: again, features are similar to ARDS in the initial stages with bilateral, diffuse ground glass and airspace consolidation. This can develop into traction bronchiectasis and cystic changes
• Lung biopsy is essential for diagnosis and histology typically shows diffuse alveolar damage

Management usually consists of high-dose steroids and antibiotics, as well as supportive measures such as high-flow O2 and often mechanical ventilation.