Lung abscess

Background

Microbiology

• Usually polymicrobial, including oral anaerobes
• Can also be monomicrobial, caused by Klebsiella, Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia pseudomallei (melioidosis), Pasteurella multocida, Streptococcus pyogenes, Haemophilus influenzae types b and c, Legionella species, Rhodococcus equi, Actinomyces species, and Nocardia species

Pathophysiology

• Mostly from chronic aspiration

Risk Factors

• Chronic aspiration from any etiology
  • Alcohol use disorder
  • Seizure disorder, stroke, drug overdose, general anesthesia
• Dysphagia or respiratory dysfunction from ALS, Parkinson disease, or stroke
• Tooth extraction

Clinical Presentation

• Cough, fever, night sweats
• Anaerobes more likely to be involved when symptoms are subacute or indolent (lasting longer than 2 weeks)

Differential Diagnosis

• See cavitary lung lesion

Investigations

• Routine investigations: CT chest, sputum for Gram stain (though may not grow anaerobes), blood cultures
• If easy to obstain, can consider transtracheal aspirates, transthoracic needle aspirates, and pleural fluid culture
• If diagnosis is uncertain, bronchoscopy

Diagnosis

• Usually made based on CT chest plus compatible symptoms

Management

• Unless clearly monomicrobial, should treat broadly and include good anaerobic coverage
  • Either a β-lactam plus metronidazole, or clindamycin
  • Possibly amoxicillin-clavulanic acid or moxifloxacin, though anaerobic coverage may not be adequate
• Duration depends on clinical and radiographic response
  • As short as 3 weeks, but usually up to 6 to 8 weeks
  • Can follow progress radiographically, continuing until chest x-ray shows small, stable residual lesion or is clear
• Rarely requires surgical intervention for lobectomy or pneumonectomy
  • Indicated in failure of medical management, suspected neoplasm, or hemorrhage
  • May also be indicated if slow response with obstructed bronchus, large abscess (>6 cm diameter), or resistant organisms (such as Pseudomonas aeruginosa)
  • If poor surgical candidate, can consider endoscopic or percutaneous drainage