Acute interstitial pneumonia

Acute interstitial pneumonitis (AIP),  isalso know as Hamman-Rich syndrome is a rapidly progressive non infectiousinterstitial 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 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 histologically by diffuse alveolar damage (DAD) ². The alveolar damage comprises of three three phases:

• acute exudative phase
• subsequent organising phase
• final fibrotic 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 the initial stages stages AIP can can have similar features to adult respiratory distress syndrome (ARDS).

Features include:

• areas with ground-glass attenuation: generally tends to be bilateral and symmetrical ¹⁰
• traction bronchiectasis: can be seen in ~80% of cases during the course of the disease ⁴ and correlates with disease duration ²
• lung parechymal architectural distortion
• air space consolidation: may have a slight predilection towards the dependent portions ⁵

Treatment and prognosis

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

History and etymology

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

Differential diagnosis

Considerations in early stages include

• adult respiratory distress syndrome (ARDS): can have other organ involvement ⁹
• infectious multifocal pneumonia
  • atypical: e.g mycoplasma pneumonia
  • bacterial pneumonia
  • severe acute respiratory syndrome (SARS)

For a more general differential, consider

• differential diagnosis of diffuse air space consolidation
• differential diagnosis of ground glass opacification