Pneumonia, Anaerobic, & Lung Abscess

Essentials of Diagnosis

• History of or predisposition to aspiration

• Indolent symptoms, including fever, weight loss, malaise

• Poor dentition

• Foul-smelling purulent sputum (in many patients)

• Opacity in dependent lung zone, with single or multiple areas of cavitation or pleural effusion

General Considerations

• Nocturnal aspiration of small amounts of oropharyngeal secretions is typically not pathologic

• Larger aspirations may cause

  • Nocturnal asthma

  • Chemical pneumonitis

  • Bronchiectasis

  • Mechanical obstruction

  • Pleuropulmonary infection

• Predisposing factors include

  • Drug or alcohol use

  • Seizures

  • Anesthesia

  • CNS disease

  • Trachea or nasogastric tubes

• Periodontal disease and poor oral hygiene are associated with a greater likelihood of pleuropulmonary infection

• Disease usually occurs in dependent lung zones

• Most infections include multiple anaerobic bacteria

  • Prevotella melaninogenica

  • Peptostreptococcus

  • Fusobacterium nucleatum

  • Bacteroides

Symptoms and Signs

• Onset is insidious; necrotizing pneumonia, abscess, or empyema may be apparent at presentation

• Constitutional symptoms of fever, malaise, and weight loss are common

• Cough with foul-smelling expectorant suggests anaerobic infection

• Poor dentition is typical; patients are rarely edentulous

• Occurrence in an edentulous patient suggests an obstructing bronchial lesion

Differential Diagnosis

• Other causes of cavitary lung disease

  • Tuberculosis

  • Fungal infection

  • Bronchogenic cancer

  • Pulmonary infarction

  • Granulomatosis with polyangiitis

  • Cavitary bacterial pneumonia

• Fungal infection, eg, histoplasmosis

• Bronchiectasis

Laboratory Tests

• Culture of expectorated sputum is not useful due to contamination with oral flora

Imaging Studies

• Chest radiograph in a lung abscess shows a thick-walled cavity surrounded by consolidation, occasionally with an air-fluid level

• Chest radiograph in necrotizing pneumonia demonstrates multiple areas of cavitation within an area of consolidation

• Empyema is characterized by purulent pleural fluid and may accompany the findings of abscess or necrotizing pneumonia

• Ultrasonography may identify loculations or help localize fluid for safe thoracentesis

Diagnostic Procedures

• Representative material for culture can be obtained only by

  • Transthoracic aspiration

  • Thoracentesis

  • Bronchoscopy with a protected brush

Medications

• Clindamycin (600 mg every 8 hours intravenously, then 300 mg every 6 hours orally after initial improvement)

• Amoxicillin-clavulanate (875 mg/125 mg every 12 hours orally)

• Penicillin (amoxicillin 500 mg every 8 hours orally or penicillin G 1–2 million units every 4–6 hours intravenously) plus metronidazole 500 mg every 8–12 hours orally or intravenously

• Penicillin alone is inadequate treatment

• Therapy should be continued until the chest radiograph improves, usually for a month or more

Surgery

• Open pleural drainage is sometimes needed because of loculations associated with a parapneumonic effusion

Therapeutic Procedures

• Thoracentesis

• Thoracostomy tube drainage for empyema in anaerobic pleuropulmonary infection

Follow-Up

• Monitor with chest radiography; if radiograph does not improve, consider other causes

Prevention

• Good dental hygiene

Prognosis

• Excellent with appropriate antimicrobial therapy

When to Refer

• Refer to infectious disease expert, pulmonary specialist, or thoracic surgeon if no response to antibiotic therapy or concern about the presence of another process (eg, cancer)

When to Admit

• Hypoxemia

• Severe malnutrition

• Marked systemic symptoms