Synonyms: pyogenic lung infection/pneumonia, necrotising pneumonia
Severe, localised suppurative infection in the substance of the lung, associated with necrotic cavity formation. The process is usually surrounded by a fibrous reaction, forming the abscess wall. Multiple small abscess formation may occur and is sometimes referred to as necrotising pneumonia.
The most frequent cause is aspiration of anaerobic organisms from the mouth in those predisposed to pulmonary aspiration, with impaired immune defences and cough reflex. A pneumonitis develops which progresses to abscess formation over a period of days or weeks.
- Inhalation of foreign body.
- Bacteraemia seeding in the lungs.
- Tricuspid endocarditis leading to septic pulmonary embolus.
- Extension of hepatic abscess.
- Associated with lung cancer.
- Proximal to bronchial obstruction.
- Complication of severe or incompletely treated pneumonia (particularly staphylococci or klebsiellae).
- Penetrating pulmonary trauma - eg, a stab wound.
NB: lung abscesses may present acutely or more chronically.
Types of lung abscesses
- Primary abscess - occurs in previously normal lungs and may follow aspiration.
- Secondary abscess - occurs in patients with an underlying lung abnormality.
Common pathogens causing lung abscess include anaerobes, Staphylococcus aureus and enteric Gram-negative rods like Klebsiella pneumoniae.
- Peptostreptococcus spp.
- Bacteroides spp.
- Fusobacterium spp.
- Microaerophilic streptococci
- S. aureus
- Streptococcus pyogenes
- Haemophilus influenzae
- Pseudomonas aeruginosa
- K. pneumoniae - becoming more prevalent
- Burkholderia cepacia - particularly associated with cystic fibrosis
- Streptococcus pneumoniae
- Legionella pneumonia
- Actinomyces spp.
- Nocardia spp.
- Proteus mirabilis
- Pasteurella multocida - zoonotic infection from cats/dogs/cattle
- Burkholderia pseudomallei - soil-borne Asian/Australian infection; cases occurred following the tsunami disaster in 2004
- Mycobacterial infections - predominantly tuberculosis (TB)
- Fungal lung infections such as Aspergillus, Cryptococcus, Histoplasma, Blastomyces, Coccidioides species
- Parasites such as Entamoeba histolytica, Paragonimus spp.
Incidence and prevalence figures have not been established.
- Alcoholism or drug misuse.
- Following general anaesthesia.
- Diabetes mellitus.
- Severe periodontal disease.
- Stroke/cerebral palsy/cognitive impairment/impaired consciousness leading to increased risk of aspiration.
- Immunosuppression, particularly chronic granulomatous disease in children.
- Congenital heart disease.
- Chronic lung disease, particularly cystic fibrosis.
- Onset of symptoms is often insidious (more acute if following pneumonia)
- Spiking temperature with rigors and night sweats
- Cough ± phlegm production (frequently foul-tasting and foul-smelling and often blood-stained)
- Pleuritic chest pain
- Finger clubbing in chronic cases
- High temperature
- Localised dullness to percussion (if consolidation is also present or effusion)
- Bronchial breathing and/or crepitations (if consolidation is present)
- Also look for signs of severe periodontal disease and infective endocarditis
- Other causes of chest infection or pneumonia - eg, TB and opportunistic mycobacteria
- Neoplasia - eg, cavitating bronchial carcinoma
- Pulmonary infarction or pulmonary embolism
- Vasculitis - eg, Wegener's granulomatosis
- Sarcoidosis with cavities
- Infected bronchogenic cyst
- FBC - normocytic anaemia or neutrophilia.
- Renal function.
- Liver function tests.
- Blood cultures and sputum cultures (including AAFB).
- ESR/CRP usually elevated.
- CXR - shows walled cavity, usually with a fluid level; may also be presence of an empyema or effusion.
- Tapping or draining of fluid or empyema with microbiology and cytology of samples.
- CT scan of the thorax - may detect multiple small abscesses.
- Fibre-optic bronchoscopy can exclude obstruction and provide samples for culture.
- Trans-thoracic biopsy/aspiration (usually with ultrasound guidance) or trans-tracheal biopsy.
- Oxygen if required
- Rehydration if indicated
- Postural drainage with chest physiotherapy
Most lung abscesses (80-90%) are now successfully treated with antibiotics.
- Begin with intravenous treatment, usually for about 2-3 weeks, and follow with oral antibiotics for a further 4-8 weeks.
- Recommended first-line therapy includes beta-lactam/beta-lactamase inhibitor or cephalosporin (second- or third-generation) plus clindamycin.
Previously, therapy with a broad-spectrum penicillin and clindamycin was used. Clindamycin had also been used alone (covers S. aureus and anaerobes and both oral and intravenous preparations exist); however, in the 1990s it was discovered that some anaerobes were resistant to both penicillin and clindamycin.
- An alternative regimen is to begin with a broad-spectrum cephalosporin and flucloxacillin.
- Regimen should be altered once the organism is known.
- If the condition fails to resolve with conservative measures, bronchoscopy, CT-guided percutaneous drainage or cardiothoracic surgical intervention may be required.
- Surgery is associated with a number of complications, such as empyema and bronchoalveolar air leak - especially so in children.
Where slow resolution occurs, the possibility of malignancy or unusual organisms must be considered.
- Bronchopleural fistula
- There is an overall 90% cure rate with antibiotic therapy.
- Morbidity and mortality are more likely to be associated with underlying pathology such as bronchial carcinoma.
- Prognosis is adversely affected by older age and multiple comorbidities.
- Other poor prognostic factors include pneumonia, reduced level of consciousness, anaemia and infection with P. aeruginosa, S. aureus and K. pneumoniae.
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