Acute interstitial pneumonitis

Acute interstitial pneumonitis (AIP), also know as Hamman-Rich syndrome is a rapidly progressive non-infectious interstitial lung disease of unknown aetiology. It is considered the only acute process of the idiopathic interstitial pneumonias.

AIP (without an underlying cause) tends to occur in those without pre-existing lung disease and typically affects middle-age adults (mean ~ 50 years 5). However in situations certain conditions such as leflunomide-induced acute interstitial pneumonia, patients can have pre-existing lung disease.

Clinical features are varied. Patients often have a history of an antecedent prior illness such as a viral upper respiratory infection. Common initial symptoms include myalgias, arthralgias, pyrexia, chills, and malaise. Severe exertional dyspnoea develops over a matter of days to weeks 13.

AIP is characterised histologically by diffuse alveolar damage (DAD) 2. The alveolar damage comprises of three phases:

  • acute exudative phase
  • subsequent organising phase
  • final fibrotic phase

Histological features are very similar with that of the adult respiratory distress syndrome (ARDS).

The correct clinical context is vital for image interpretation.

Plain radiograph

Nonspecific and often shows bilateral patchy airspace opacification.


During the initial stages, AIP can have similar features to adult respiratory distress syndrome (ARDS). Features include:

The condition usually progresses to respiratory failure that requires mechanical ventilation and corticosteroid therapy. Even despite mechanical ventilation, it often tends to carry a grave prognosis with > 70% mortality at ~ 3 months 1.

  • clinical features first described by L Hamman and A Rich in 1935 8
  • pathological processes first described by A L Katzenstein et al. in 1986 3

Considerations in early stages include:

Other considerations include:

For a more general differential, consider:

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Article Information

rID: 10993
System: Chest
Section: Pathology
Synonyms or Alternate Spellings:
  • Acute interstitial pneumonia
  • AIP
  • Acute interstitial pneumonitis (AIP)
  • Hamman-Rich syndrome

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