Lung abscess

[Jenny_94]

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can anyone tell me why bronchogenic carcinoma causes lung abscess? And why S.aureus is the most common bacteria in this case. I would like to know the mechanism on why the obstruction of the bronchus causes abscess.

 

[tasar1898]

Obstructing bronchoCa causes partial/total atelectasis of the distal segment + Necrotic infected debris from tumor = Post obstruction pneumonia with secondary abscess formation.. I don't have a clue why s.aureus is the most common but I know aspiration = anaerobes , diabetics/post pneumonia/alcoholics= s.aureus/klebsiella and hematogenous from endocarditis = s .aureus and streptococcus species . Alcoholics/seizure disorders/drug addicts/pts under anesthesia can also get aspiration with anaerobes

 

[worldbeater]

[QUOTE=". I don't have a clue why s.aureus is the most common [/QUOTE]

Staph aureus is always present on your skin, so it can be introduced into your lungs. This is also why IV drug users present with infection of the tricuspid valve; when your using an IV drug, your introducing the staph aureus bacteria into your blood stream, and the first valve it touches is the tricuspid valve.

 

[Jenny_94]

okay so i get that obstruction causes atelectasis. But why would that cause infection?
Also i dont understand about the debris of the tumor.

 

[Phloston]

Lung abscess is treated with clindamycin. That's really HY for the USMLE. Anaerobes above the diaphragm big time. And Bacteroides is the big one.

I definitely would caution against any type of mention that S. aureus is a common cause of lung abscess. S. aureus is often the answer for bacterial superinfection following influenza LRTI, or in nosocomial infections. But lung abscesses are often secondary to aspiration (dementia, stroke, epilepsy) of oropharyngeal anaerobes.

UpToDate on lung abscess:

http://www.uptodate.com/contents/lu...lectedTitle=1~72&sectionRank=1&anchor=H16#H16

 

[worldbeater]

Lung abscess is treated with clindamycin. That's really HY for the USMLE. Anaerobes above the diaphragm big time. And Bacteroides is the big one.

I definitely would caution against any type of mention that S. aureus is a common cause of lung abscess. S. aureus is often the answer for bacterial superinfection following influenza LRTI, or in nosocomial infections. But lung abscesses are often secondary to aspiration (dementia, stroke, epilepsy) of oropharyngeal anaerobes.

UpToDate on lung abscess:

http://www.uptodate.com/contents/lu...lectedTitle=1~72&sectionRank=1&anchor=H16#H16

Good call on trying not to associate staph aureus with lung abscess.

Also just to complete your thought about anaerobes, clindamycin is used for above the diaphragm and metronidazole is used for any anaerobes found below the diaphragm. The diaphragm is your landmark to figure out what drug to use.

To the original poster, one pattern I noticed about lung abscesses is they won't outright say it in the vignette. They will say something like "air/fluid levels are present in the lung", which is code for abscess. What is an abscess? - half air/half fluid.

 

[tasar1898]

@Phloston Bacteroides is abscess below diaphragm right?? I think I remember the General Surgeons cursing at this microbe all the time in the hospital

 

[Phloston]

@Phloston Bacteroides is abscess below diaphragm right?? I think I remember the General Surgeons cursing at this microbe all the time in the hospital

Bacteroides is found throughout the GI tract and yes can cause diverticulitis, abscesses and other infections below the diaphragm.