What is Lung Abscess?
A lung abscess is when pus or dead tissue builds up inside the lung, causing a hollow space to form. When a path opens between the lungs and the bronchi (the tubes that carry air in and out of the lungs), this space often shows a level of fluid and air. Lung abscesses can be grouped with other lung infections like lung gangrene (tissue death due to lack of blood supply) and necrotizing pneumonia, which can lead to several abscesses.
Lung abscesses are usually classified based on how long they last: acute ones resolve within 6 weeks, while chronic ones last more than 6 weeks. They can also be categorized based on what causes them. Primary lung abscess mainly occurs after accidentally inhaling oral secretions, which can be due to various conditions like dental or gum infections, sinusitis, swallowing disorders and more. Secondary lung abscesses occur because of lung-related issues such as blockages due to growths, conditions like cystic fibrosis or lung contusions (bruising).
These types of abscesses can also be grouped based on how they spread from outside the lungs. This could be through the blood (from abdominal infection, heart infection etc.) or directly from other infected areas (bronchoesophageal fistulas or subphrenic abscesses).
Early signs of a lung abscess are similar to pneumonia including fever, chills, night sweats, and chest pain. As the condition develops, a producing cough also becomes a key symptom. Tests, such as CT scans and thoracic ultrasounds, help identify and characterize lung abscesses. Additional tests, including sputum examination and bronchoscopy (examining the airways using a flexible tube), are crucial in identifying the cause and differentiating lung abscesses from other conditions like cavitary tuberculosis and lung cancer.
Complications can include pyopneumothorax or pleural empyema, especially in people with a weak immune system. Treatment typically starts with antibiotics that cover a broad range of bacteria, with adjustments made based on specific bacteria found. Factors that can affect outcomes negatively include old age, serious health problems, and a compromised immune system. Surgery or percutaneous procedures might be necessary for larger abscesses or when medication doesn’t work. Treatment usually lasts about 3 weeks, switching to oral antibiotics once the patient’s condition stabilizes.
What Causes Lung Abscess?
Primary lung abscesses – pockets of pus in the lung – usually occurs as a single instance and develops in people who are typically healthy. On the other hand, secondary lung abscesses usually develop in people who have certain pre-existing medical conditions and often result in multiple areas of pus in the lung.
We categorize a lung abscess as nonspecific when doctors cannot identify a specific germ that has caused it from the spit the patient coughs up. If they believe a type of germ that doesn’t need oxygen (anaerobic bacteria) caused the abscess, they classify it as a putrid abscess. The exact type of germ causing the abscess determines the classification. In most cases, many types of germs, including bacteria that do not need oxygen to survive (such as Bacteroides, Prevotella, Peptostreptococcus, Fusobacterium, or streptococci), cause the abscess.
Sometimes only one type of germ causes a lung abscess. This could be streptococci, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pyogenes, Burkholderia pseudomallei, Hemophilus influenzae type b, Nocardia, or Actinomyces.
In people with alcohol use disorder, the germs commonly causing a lung abscess include Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pyogenes, and Actinomyces. Poor dental hygiene also increases the risk of developing lung abscesses.
People who have undergone lung transplants have a higher chance of developing an infection from the Mycobacterium abscessus complex compared to other organ transplant patients. This is due to the higher levels of immune system suppression needed after lung transplants compared to other organ transplants. Also, lung transplant recipients have large amounts of specialized immune cells (donor-derived dendritic cells) that can activate other immune cells (T-cells) and react to germs from the environment, which can lead to the body rejecting the new organ.
Risk Factors and Frequency for Lung Abscess
- People with weakened immune systems, such as those with HIV-AIDS, those who have had a transplant, or those under long-term immune suppressive therapy, are more likely to develop a lung abscess.
- People at high risk of inhaling foreign materials into their lungs, like those with seizures, dysfunction of the nerve control for the throat, those under the influence of alcohol, or people with cognitive impairments, are also commonly predisposed to lung abscesses.
Signs and Symptoms of Lung Abscess
A lung abscess can be quite similar to pneumonia in its early stages, presenting symptoms like fever, chills, cough, night sweats, shortness of breath, weight loss, tiredness, and chest pain. Sometimes it may also lead to anemia. In the beginning, the cough tends to be dry, but turns productive – characterized by the secretion of mucus or phlegm – when bronchial communication, a key feature of lung abscess, develops. Occasionally, this cough may involve coughing up blood.
It’s crucial to note that lung abscesses need to be differentiated from other conditions such as cavitary tuberculosis and mycoses, even though these rarely display the X-ray sign of a gas-liquid level. Cavitating bronchial carcinomas, such as squamous cell or small cell carcinomas, usually have thicker, more irregular walls than infectious lung abscesses. If fever, pus-like sputum, and an increase in the number of white blood cells are not present, it could be a sign towards a carcinoma rather than an infection.
Testing for Lung Abscess
Chest X-rays and CT scans are useful tools in diagnosing a lung abscess, which is a pus-filled cavity in the lung. It can be tricky to tell the difference between a lung abscess and other lung issues, such as bronchial cysts, sequestration, or infected emphysematous bullae. But the location and symptoms of the lesion, along with these scans, can help guide the diagnosis.
In some cases, doctors might use CT scans or an ultrasound to identify a localized pleural empyema – a condition where pus collects in the pleural space, the area between the lung and the chest wall. A particular sign of abscess, where you can see an air-fluid level, might also be observed in cases of hydatid cysts in the lung.
An examination of the sputum (mucus that is coughed up from the lungs) can help identify the germs causing the infection or confirm if lung cancer is present. Details about the patient’s history like exposure to certain environments or past diseases can guide doctors to request specific cultures during this test.
Sometimes, a procedure called a bronchoscopy may be needed. During this procedure, a doctor uses a thin tube with a camera on the end to look inside the lungs and collect samples. This is important for confirming the cause of the abscess. In rare cases, doctors might also analyze the fluid in the pleural space or use bronchoalveolar lavage, a procedure where a saltwater solution is used to collect cells and other materials from the lungs.
Lung abscesses are more likely to develop in certain parts of the lungs, especially following the inhalation of contents from the mouth and throat. Complications such as pyopneumothorax (air and pus in the chest cavity) or pleural empyema can occur, particularly in people with weakened immune systems. When these complications happen, analyzing the fluid in the pleural space can help in making a diagnosis.
However, people with normal immune systems who receive proper treatment are less likely to experience complications and usually recover within 3 weeks. If a lung abscess happens because of a blood infection, then testing of the blood (cultures) and ultrasound of the heart (echocardiography) are essential to guide treatment.
Treatment Options for Lung Abscess
Doctors often recommend antibiotic treatment when they suspect a patient has a lung abscess. The chosen antibiotics should combat bacteria commonly found in the mouth and throat, including a variety of cocci and bacilli. If the patient has been in a healthcare setting within 3 months before showing symptoms, antibiotics capable of treating MRSA (a type of bacteria that is resistant to many antibiotics) should be considered.
Sometimes, the usual “broad-spectrum” antibiotics (those that can treat a wide range of bacteria) may not work, and doctors will look for unusual organisms causing the infection. Patients who are older, have other severe health conditions, have reduced immune system function, or have blockages in the airways or tumors may respond less well to treatment. Initial antibiotic choices usually include certain types of drugs that inhibit beta-lactamase, an enzyme that some bacteria produce to resist antibiotics, followed by imipenem or meropenem.
Clindamycin is no longer commonly recommended as the first choice of treatment for lung abscess due to the risk of a serious gut infection caused by Clostridium difficile. However, it can be an alternative for patients who are allergic to penicillin. If MRSA is suspected, vancomycin or linezolid are the preferred choices. Daptomycin, another antibiotic, has no activity against infections in the lungs. For methicillin-sensitive Staphylococcus aureus, a type of bacteria, doctors often use cefazolin, nafcillin, or oxacillin.
Doctors might need to adjust the dosage for patients with kidney problems. Usual duration of antibiotic use is about 3 weeks, but it can vary depending on how a patient is responding to treatment. Once patients are fever-free, stable, and can tolerate food by mouth, doctors may switch them to oral antibiotics. Amoxicillin-clavulanate is generally the preferred oral antibiotic for treating lung abscesses. Metronidazole alone doesn’t seem to be very useful because lung abscesses often involve a mix of different bacteria.
Abscesses larger than 6 cm probably won’t go away with just antibiotic therapy and might require surgical or other procedures to drain the accumulation of pus. If medical treatment doesn’t work, surgery to remove part or all of the lung might be considered. For patients who are not fit for surgery, drainage of the abscess through the skin or using an endoscope (a flexible tube with a camera) can be considered. If the treatment is not working well, doctors might suspect other diseases, including certain kinds of fungal and bacterial infections or empyema (a condition where pus fills the space between the lungs and the chest wall). Sometimes a lung abscess might be caused by infection elsewhere in the body, like infective endocarditis (infection of the heart valves) or a blood clot resulting from an infection (septic thromboembolism). These underlying conditions should also be treated. Regular antibiotic administration can be beneficial for chronic lung abscesses.
What else can Lung Abscess be?
When diagnosing a lung abscess, doctors should also consider other conditions that may have similar symptoms. These include:
- Bronchial carcinoma (either squamocellular or microcellular)
- Tuberculosis that causes excavation
- Localized pleural empyema
- Infected emphysematous bullae
- Cavitary pneumoconiosis
- Hiatal hernia
- Pulmonary hematoma
- Hydatid cyst of the lung
- Cavitary infarcts of the lung
- Polyangiitis with granulomatosis (Wegener granulomatosis)
- Foreign body aspiration
- Septic pulmonary emboli
To ensure an accurate diagnosis, the doctor might conduct tests that rule out any of these possibilities.
What to expect with Lung Abscess
In most instances, primary lung abscesses, which are pockets of pus that form inside or on the lungs due to an infection, are treated effectively with antibiotics. The type of antibiotics are initially chosen based on best guesses (this is termed “empiric therapy”), then adjusted based on the specific type of bacteria detected in lab tests. This approach has approximately a 90% success rate.
However, secondary lung abscesses, which are caused by other underlying health issues, require these underlying issues to be treated to get better. Unfortunately, the outlook isn’t as positive for patients with secondary lung abscesses, especially those with weakened immune systems or individuals with bronchial neoplasm (a growth in the air passages leading into the lungs). For these patients, the mortality rate tends to be high, at approximately 75%.
Possible Complications When Diagnosed with Lung Abscess
Problems that arise from untreated or improperly treated lung abscesses can be serious. These complications can include the abscess breaking into the space around the lungs, scarring in these spaces, lungs becoming encased and failing, fistulas (or abnormal connections) forming between the lung and the skin or the lung and the bronchial tubes.
List of Complications:
- Abscess rupture into the pleural space
- Pleural fibrosis
- Trapped lung
- Respiratory failure
- Bronchopleural fistula
- Pleurocutaneous fistula
Preventing Lung Abscess
Educating patients and their caregivers about how to reduce the risk of inhaling substances into the lungs is crucial in preventing the development of a lung abscess, which is a pocket of pus in the lungs. Strategies include avoiding drinking too much alcohol, taking good care of teeth and gums, and elevating the head end of the bed.
Healthcare providers should also teach patients and their families to quickly recognize the signs of a lung abscess, which may include fever, difficulty breathing, and cough that may or may not produce mucus or phlegm.
Ensuring that patients take their antibiotics properly and watch out for any negative side effects is also key to avoiding further complications. In simple terms, consistent and correct use of prescribed antibiotics is necessary and any unusual changes or feelings after taking these medicines should be reported immediately.
