Purulent fluid collection in the pleural space, most commonly caused by pneumonia

Aetiology

• Majority of cases are as a complication of pneumonia
• Remainder are primary empyema (iatrogenic or idiopathic)

Risk factors

• Immunodeficiency
• Immunosuppression
• Abnormal innate immunological defence
• Repeated insult e.g. aspiration

Pathophysiology

1. Simple pleural effusion (pH >7.2, high glucose, negative gram stain)
2. Complicated pleural effusion (pH <7.2, low glucose, positive gram stain)
3. Empyema (mostly aerobic organisms, sometimes anaerobes e.g. from severe pneumonia)

Clinical features

• Slow to resolve pneumonia - typically patient will partially recover, then will develop a spike in temperature
• May be signs of pleural effusion on examination

Investigations

• Imaging:
  • CXR: fluid level
  • USS: to confirm a collection of pleural fluid, may be used for thoracentesis (will be pus)
  • CT: not routinely used, can differentiate between an empyema and an abscess

Management

• Broad spectrum IV antibiotics initially (amoxicillin and metronidazole)