Chapter 154 - Lung Abcess

Question 1

Lung abcesses can be single or multiple but usually are marked by a single dominant cavity >2cm in diameter.
True or False?

Answer 1

True.

Question 2

How can one classify lung abcesses regarding its etiology and its duration?

Answer 2

“Lung abscesses are usually characterized as either primary (~80% of cases or secondary. Primary lung abscesses usually arise from aspiration, are often caused principally by anaerobic bacteria, and occur in the absence of an underlying pulmonary or systemic condition. Secondary lung abscesses arise in the setting of an underlying condition, such as postobstructive process (e.g., a bronchial foreign body or tumor) or a systemic process (e.g., HIV infection or another immunocompromising condition). Lung abscesses can also be characterized as acute (less than 4-6 weeks in duration) or chronic (~40% of cases).

Question 3

Which patients are more commonly affected by lung abscesses?

Answer 3

Middle-aged men (primary abscesses).

Question 4

Name the risk factors for aspiration.

Answer 4

“Patients at particular risk for aspiration, such as those with altered mental status, alcoholism, drug overdose, seizures, bulbar dysfunction, prior cerebrovascular or cardiovascular events, or neuromuscular disease, are most commonly affected. In addition, patients with esophageal dysmotility or esophageal lesions (strictures or tumors) and those with gastric distention and/or gastroesophageal reflux, especially those who spend substantial time in the recumbent position, are at risk for aspiration.”

Question 5

What is the pathophysiology of lung abscesses regarding bacteria colonization and aspiration? Is there any evidence supporting this mechanisms?

Answer 5

“It is widely thought that colonization of the gingival crevices by anaerobic bacteria or microaerophilic streptococci (especially in patients with gingivitis and periodontal disease), combined with a risk of aspiration, is important in the development of lung abscesses. In fact, many physicians consider it extremely rare for lung abscesses to develop in the absence of teeth as a nidus for bacterial colonization.”

“The importance of these risk factors in the development of lung abscesses is highlighted by a significant reduction in abscess incidence in the late 1940s that coincided with a change in oral surgical technique: beginning at that time, these operations were no longer performed with the patient in the seated position without a cuffed endotracheal tube, and the frequency of perioperative aspiration events was thus decreased.”

Question 6

The introduction of penicillin has reduced the incidence and mortality rate from lung abscesses.
True or False?

Answer 6

True.

Question 7

Summarize the pathogenesis of primary lung abcesses.

Answer 7

“The development of primary lung abscesses is thought to originate when chiefly anaerobic bacteria (as well as microaerophilic streptococci) in the gingival crevices are aspirated into the lung parenchyma in a susceptible host. Thus, patients who develop primary lung abscesses usually carry an overwhelming burden of aspirated material or are unable to clear the bacterial load. Pneumonitis develops initially (exacerbated in part by tissue damage caused by gastric acid); then, over a period of 7-14 days, the anaerobic bacteria produce parenchumal necrosis and cavitation whose extent depends on the host-pathogen interaction. Anaerobes are thought to produce more extensive tissue necrosis in polymicrobial infections in which virulence factors of the various bacteria can act synergistically to cause more significant tissue destruction.”

Question 8

Name the pathogens that might be involved in a primary lung abscess.

Answer 8

Anaerobes (e.g., Peptostreptococcus spp., Prevotella spp., Bacteroides spp., Streptococcus milleri), microaerophilic streptococci.

Question 9

Summarize the pathogenesis of secondary lung abscesses, namely local and systemic factors.

Answer 9

“The pathogenesis of secondary abscesses depends on the predisposing factor. For example, in cases of bronchial obstruction from malignancy or a foreign body, the obstructing lesion prevents clearance of oropharyngeal secretions, leading to abscess development. With underlying systemic conditions (e.g., immunosuppresion after bone marrow or solid organ transplantation), impaired host defense mechanisms lead to increased susceptibility to development of lung abscesses caused by a broad range of pathogens, including opportunistic organisms.”

Question 10

Name the pathogens that might lead to secondary lung abcesses.

Answer 10

Staphylcoccus aureus, gram-negative rods (e.g., Pseudomonas aeruginosa, Enterobacteriaceae), Nocardia spp., Aspergillus spp., Mucorales, Cryptococcus spp., Legionella spp., Rhodococcus equi, Pneumocystis jirovecii.

Question 11

Describe Lemierre’s syndrome.

Answer 11

“Lemierre’s syndrome, in which an infection begins in the pharynx (classically involving Fusobacterium necrophorum) and then spreads to the neck and the carotid sheath (which containts the jugular vein) to cause septic thrombophlebitis.”

Question 12

Which pathogen is commonly involved in abcesses due to embolic lesions? How does one explain this finding?

Answer 12

Embolic lesions are mostly due to Staphylococcus aureus, since the emboli are derived from endocarditis, often the tricuspid valve. Right valve endocarditis is especially frequent among those who inject intravenous drugs, leading to the entrance of skin organisms in the systemic circulation.

Question 13

Which pulmonary lobes are more susceptible for primary lung abscesses? And secondary lung abscesses?

Answer 13

“In primary lung abscesses, the dependent segments (posterior upper lobes and superior lower lobes) are the most common locations, given the predisposition of aspirated materials to be deposited in these areas. Generally, the right lung is affected more commonly than the left because the right mainstem bronchus is less angulated. In secondary abscesses, the location of the abscess may very with the underlying cause.”

Question 14

Primary lung abscesses are mostly due to a single bacteria infection.
True or False?

Answer 14

False.

Usually these are polymicrobial.

Question 15

How can one increase the retrieval and culture growth of anaerobic bacteria? How high is the rate of retrieval?

Answer 15

“The retrieval and culture of anaerobes can be complicated by the complicated by the contamination of samples with microbes from the oral cavity, the need for expeditious transport of the cultures to the laboratory, the need for early platting with special culture techniques, and the need for collection of specimens prior to administration of antibioticsWhen attention is paid to these factors, rates of recovery of specific isolates have been reported to be as high as 78%.”

Question 16

The identification of the causative organism lung abscess is important for therapeutic decisions and should always be obtained when possible.
True or False?

Answer 16

True: Secondary lung abscess - “Because immunocompromised hosts and patients without the classic presentation of a primary lung abscess can bve infected with a wide array of unusual organisms, it is of special importance to obtain culture material in order to target therapy.”
False: Primary lung abscess - “it is not clear that knowing the identity of the causative anaerobic isolate alters the response to treatment.”

Question 17

Describe a nonspecific and a putrid lung abscess.

Answer 17

“When no pathogen is isolated from a primary lung abscess (which is the case as often as 40% of the time), the abscess is termed a nonspecific lung abscess, and the presence of anaerobes is often presumed. A putrid lung abscess refers to foul-smelling breath, sptum or empyema and is essentially diagnostic of an anerobic lung abscess.”

Question 18

What are the most common pathogens involved in secondary lung abscesses?

Answer 18

Pseudomonas aeruginosa and other gram-negative rods.

Question 19

Name the causes of digital clubbing.

Answer 19

• Cardiology: cyanotic congenital heart disease (Eisenmenger’s syndrome, Fallot’s tetralogy and transposition of the great vessels) and infective endocarditis.
• Pneumology: lung abscesses, primary and secondary lung neoplasia, mesothelioma, sarcoidosis, tuberculosis, asbestosis, bronchiectasias, cystic fibrosis, idiopathic pulmonary fibrosis.
• Gastroenterology: hepatic cirrhosis and intestinal inflammatory diseases.
• Acquired: pneumatic workers.
• Familial: normal variant.

Question 20

Summarize the clinical manifestations of lung abscess. Also, compare the presentation of those with S. aureus versus anerobic infection.

Answer 20

“Clinical manifestations may initially be similar to those of pneumonia with fevers, cough, sputum production, and chest pain; a more chronic and indolent presentation that includes night sweats, fatigue, and anemia is often observed with anaerobic lung abscesses. A subset ofpatients with putrid lung abscesses may report discolored phlegm and foul-tasting or foul-smelling sputum. Patients with lung abscesses due to non-anaerobic organisms, such as S. aureus, may presents with a more fulminant course characterized by high fevers and rapid progression.”

“Findings on physical examination may include fevers, poor dentition, and/or gingival disease as well as amphoric andor cavernous breath sounds on lung auscultation. Additional findings may include digital clubbing and the absence of a gag reflex.”

Question 21

CT helps distinguish between a lung abscess from a pleural infection, which is important due to the fact that the latter may require urgent drainge (as in empyema).
True or False?

Answer 21

True.

Question 22

Regarding primary lung abscesses, why is it that Gram’s stain and culture of sputum or other materials is not often performed?

Answer 22

“While sputum can be collected noninvasively for Gram’s stain and culture, which may yield a pathogen, it is likely that the infection will be polymicrobial, and culture results may not reflect the presence of anaerobic organisms.” Therefore, one treats empirically with anaerobic coverage.

Question 23

Many physicians consider putrid-smelling sputum to be virtually diagnostic of an anerobic infection.
True or False?

Answer 23

True.

Question 24

When should one use collect sputum and blood cultures, as well as invasive testing for the identification of the pathogen(s) involved in lung abscess?

Answer 24

“When a secondary lung abscess is present or empirical therapy fails to elicit a response, sputum and blood cultures are advised in addition to serologic studies for opportunistic pathogens (e.g., viruses and fungi causing infections in immunocompromised hosts). Additional diagnostics, such as bronchoscopy with bronchoalveolar lavage or protected brush specimen collection and CT-guided percutaneous needle aspiration, can be undertaken.”

Question 25

What are the risks of invasive diagnostic testing for lung abscess?

Answer 25

“Risks posed by these more invasive diagnostics include spilalge of abscess contents into the other lung (with bronchoscopy) and pneumothorax and bronchopleural fistula development (with CT-guided needle aspiration).”

Question 26

Summarize the treatment of primary lung abscesses.

Answer 26

“because oral anaerobes can produce β-lactamases, clindamycin has proved superior to penicillin in clinical trials. For primary lung abscesses, the recommended regimens are (1) clindamycin (600 mg IV three times daily; then, with the disappearance of fever and clinical improvement, 300 mg PO four times daily) or (2) an IV-administered β-lactam/β-lactamase combination, followed - once the patient’s condition is stable - by orally administered amoxicillin-clavulanate. This therapy should be continued until imaging demonstrates that the lung abscess has cleared or regressed to a small scar. Treatment duration may range from 3-4 weeks to as long as 14 weeks. One small study suggested that moxifloxacin (400mg/d PO) is a effective and well tolerated as ampicillin-sulbactam. Notably, metronidazole is not effective as a single agent: it covers anaerobic organisms but no the microaerophilic strptocci that are often components of the mixed flora of primary lung abscesses.”

Question 27

How many patients do not respond to antibiotic therapy?

Answer 27

10-20%.

Question 28

In those that do not respond to antibiotic therapy, which steps should be considered in the management and theraputics of the patient with a lung abscess?

Answer 28

“if the condition of patients with presumed primary lung abscess fails to improve, additional studies to rule out an underlying predisposing cause for a secondary lung abscess are indicated.”

“10-20% of patients may not respond at all, with continued fevers and progression of the abscess cavity on imaging. An abscess >6-8 cm in diameter is less likely to respond to antibiotic therapy without additional interventions. Options for patients who do not respond to antibiotics and whose additional diagnostic studies fail to identify an additional pathogen that can be treated include surgical resection and percutaneous drainage of the abscess, especially in poor surgical candidates.”

Question 29

Summarize the complications associated with lung abscesses.

Answer 29

“Larger cavity size on presentation may correlate with the development of persistent cystic changes (pneumatoceles) or bronchiectasis. Additional possible complications include recurrence of abscesses despite appropriate therapy, extension to the pleural space with development of empyema, life-threatening hemoptysis, and massive aspiration of lung abscess contents.”

Question 30

What is the prognosis for primary and secondary lung abscesses?

Answer 30

“Reported mortality rates for primary abscesses have been as low as 2%, while rates for secondary abscesses are generally higher - as high as 75% in some case series.”

Question 31

Name poor prognosis factors related to lung abscesses.

Answer 31

“age >60, the presence of aerobic bacteria, sepsis at presentation, symptom duration of >8 weeks, and abscess size >6cm.”

Question 32

Give examples of simple non-pharmacological methods to prevent lung abscess recurrence.

Answer 32

Airway protection, oral hygene and minimize sedation with elevation of the head of the bed for patients at risk for aspiration.

Question 33

Bronchoscopy should be performed early in patients whose history, symptoms, or imaging findings are consistent with possible bronchial obstruction.
True or False?

Answer 33

True

Question 34

Induced sputum samples should be examined early in the workup to rule out tuberculosis.
True or False?

Answer 34

True

for those who come from endemic areas or have risk factors, such as HIV infection