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Acute interstitial pneumonitis

Acute interstitial pneumonitis (AIP) is a rapidly progressive non infectious interstitial lung disease of unknown aetiology. It is considered the only acute process of the idiopathic intersitial pneumonias.

Epidemiology

AIP tends to occur in those without pre-existing lung disease and typically affects middle age adults (mean ~ 50 years 5).

Clinical presentation

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

Pathology

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).

Radiographic features

The correct clinical context is vital for image interpretation.

Plain film

Non specific and often shows bilateral patchy airspace opacification.

HRCT

During intialy stages can have similar features to adult respiratory distress syndrome (ARDS)

Features include

Treatment and prognosis

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,

Etymology

  • 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

Differential diagnosis

Considerations in early stages include

For a more general differential, consider

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