Overview
An empyema is a collection of pus within a pre-existing anatomical cavity. Pleural empyema is the collection of pus within the pleural cavity. An empyema is different to a lung abscess, as lung abscesses are collections of pus in newly-formed cavities.
A pleural empyema can develop following an infection of the lung.
Risk Factors
- Pneumonia
- Iatrogenic: thoracentesis or chest drain insertion
- Thorax trauma
- Immunodeficiency
- Pre-existing lung diseases (e.g. COPD, bronchiectasis, and lung cancer)
Presentation
Patients tend to have a subacute onset of symptoms, usually around 2 weeks. Patients who fail to respond to antibiotics or deteriorate on a background of pneumonia should raise suspicion of an empyema. Features are:
- Recent pneumonia
- Fevers and rigours
- Pleuritic chest pain
- Productive cough
- Dyspnoea
- Constitutional symptoms – fatigue, weight loss, night sweats, anorexia, malaise
- Examination may show:
- Dullness to percussion
- Reduced breath sounds
- Patients may have signs of sepsis:
- Tachypnoea
- Tachycardia
- Hypotension
Differential Diagnoses
Pneumonia
- There may be no way to differentiate them clinically
- Chest x-ray shows consolidation but no effusion
Lung abscess
- There may be no way to differentiate them clinically
- Chest x-ray shows a cavitating lung lesion with an air-fluid level
Pleural effusion
- There may be no way to differentiate them clinically
- Chest x-rays show effusions with a clear fluid level
Investigations
All patients
- Blood cultures:
- Ideally should be performed before giving antibiotics, but do not delay treatment
- Identifies causative pathogen
- White cell count:
- Usually raised due to infection
- C-reactive protein (CRP):
- Usually raised due to infection
- Chest x-ray:
- May show blunting or blurring or the costophrenic angle on the affected side
- May show an effusion on the affected side
- Thoracic ultrasound:
- Useful for guiding thoracentesis and more specific than x-rays for detecting an empyema
- The empyema may be echogenic, loculated, or septated
- Thoracentesis and fluid analysis:
- If there is pus present, an empyema can be diagnosed
- Pleural fluid findings may be:
- pH: <7.2
- Protein: >30 g/dL
- Glucose: reduced (<3.3 mmol/L)
- Lactate dehydrogenase (LDH): raised
- Cytology and white cell differential: polymorphonuclear cells present
Diagnosis
Diagnosis is based on clinical features and investigations. The presence of pus in the pleural cavity fluid is diagnostic of an empyema.
Management
All patients
- 1st-line: broad-spectrum IV antibiotics and sepsis six + chest drain insertion
- Surgery may be needed in some cases
Complications
- Septic shock
- Respiratory failure
- Complications from chest drain insertion such as pneumothorax or atelectasis
Prognosis
- Prognosis depends on the presence of comorbidities and whether the patient is immunocompromised or not