Lung abscess

Lung abscess



BASIC INFORMATION ABOUT LUNG ABSCESS


A lung abscess is an infection of the lung parenchyma resulting in a necrotic cavity containing pus.

SYNONYMS
Pulmonary abscess

EPIDEMIOLOGY & DEMOGRAPHICS
• Incidence has decreased over the last 30 years as a result of antibiotic therapy.
• Lung abscess in patients age 50 and over is associated with primary lung neoplasia in 30% of the cases.
• Lung abscesses commonly coexist with empyemas.
• Risk factor population includes patients with:
1. Alcohol-related problems
2. Seizure disorders
3. Cerebrovascular disorders with dysphagia
4. Drug abuse
5. Esophageal disorders (e.g., scleroderma, esophageal carcinoma, etc.)
6. Poor oral hygiene
7. Obstructive malignant lung disease
8. Bronchiectasis

PHYSICAL FINDINGS & CLINICAL PRESENTATION
• Symptoms are generally insidious and prolonged, occurring for weeks to months
• Fever, chills, and sweats
• Cough
• Sputum production (purulent with foul odor)
• Pleuritic chest pain
• Hemoptysis
• Dyspnea
• Malaise, fatigue, and weakness
• Tachycardia and tachypnea
• Dullness to percussion, whispered pectoriloquy, and bronchophony
ETIOLOGY
• The most important factor predisposing to lung abscess is aspiration.
• Following aspiration as a major predisposing factor is periodontal disease.
• Lung abscess is rare in an edentulous person.
• Approximately 90% of lung abscesses are caused by anaerobic microorganisms (Bacteroides fragilis, Fusobacterium nucleatum, Peptostreptococcus,
microaerophilic Streptococcus).
• In most cases anaerobic infection is mixed with aerobic or facultative anaerobic organisms (S. aureus, E. coli, K. pneumoniae, P. aeruginosa).

DIAGNOSIS
Lung abscess may be primary or secondary.
• Primary lung abscess refers to infection from normal host organisms within the lung (e.g., aspiration, pneumonia).
• Secondary lung abscess results from other preexisting conditions (e.g., endocarditis, underlying lung cancer, pulmonary emboli).
Lung abscess may be acute or chronic.
• Acute lung abscess is present if symptoms are of less than 4 to 6 wk.
• Chronic lung abscess is present if symptoms are greater than 6 wk.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis is similar to cavitary lung lesions:
• Bacterial (anaerobic, aerobic, infected bulla, empyema, actinomycosis, tuberculosis)
• Fungal (histoplasmosis, coccidioidomycosis, blastomycosis, aspergillosis, cyptococcosis)
• Parasitic (amebiasis, echinococcosis)
• Malignancy (primary lung carcinoma, metastatic lung disease, lymphoma, Hodgkin’s disease)
• Wegener’s granulomatosis, sarcoidosis, endocarditis, and septic pulmonary emboli
WORKUP
• The workup of a patient with lung abscess attempts to elicit a primary or a secondary cause.
• Blood tests are not specific in diagnosing lung abscesses.
• Most diagnoses are made from imaging studies; however, to diagnose a specific cause bacteriologic studies are needed.
LABORATORY TESTS
• CBC with leukocytosis
• Bacteriologic studies
1. Sputum Gram stain and culture (commonly contaminated by oral flora)
2. Percutaneous transtracheal aspiration
3. Percutaneous transthoracic aspiration
4. Fiberoptic bronchoscopy using bronchial brushings or bronchoalveolar lavage are the most widely used intervention when trying to obtain diagnostic bacteriologic cultures
• Blood cultures on some occasions may be positive
• If an empyema is present, obtaining empyema fluid via thoracentesis may isolate the organism
TREATMENT
NONPHARMACOLOGIC THERAPY

• Oxygen therapy
• Postural drainage
• Respiratory therapy maneuvers
ACUTE GENERAL Rx
• Penicillin 1 to 2 million units IV q4h until improvement (e.g., afebrile, decrease in sputum production, etc.) followed by penicillin VK 500 mg PO qid for the next 2 to 3 wk but usually requiring longer 6- to 8-wk courses.
• Metronidazole is given with penicillin at doses of 7.5 mg/kg IV q6h followed by PO 500 mg bid to qid dosing.
• Clindamycin is an alternative choice if concerned about penicillinresistant organisms. The dose is 600 mg IV q8h until improvement, followed by 300 mg PO q6h.
CHRONIC Rx
• Brochoscopy to assist with drainage and/or diagnosis is indicated in patients who fail to respond to antibiotics or if there is suspected underlying malignancy.
• Surgery is indicated on rare occasions (<10%) in patients with complications of lung abscess mentioned below.
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