A lung abscess happens often
in patients who are older, where the immune system is weak and where the normal
cough reflexes are modified or suppressed.
A common mechanism is aspiration of stomach contents
by vomiting and aspiration of part of the vomitus with all the bacteria from the
pharynx, or gastrointestinal tract.
Often the first step is that aspiration
pneumonia develops and out of this a lung abscess can develop. High risk persons
are alcoholics at the height of a drinking bout, patients with severe neurological
diseases such as MS, stroke, Alzheimers in stage 3, patients with a coma or patients
during major surgery when the patient is paralyzed from a general anesthetic.
The bacteria that cause a lung abscess are usually anaerobes that stem from the
gastrointestinal tract or from the oral cavity or the pharynx.
bacteria are Staphylococcus aureus, a pus bacterium that is devastating to lung
tissue due to a lytic enzyme it produces. Intravenous drug users who work with
contaminated needles may end up with this bacterium in the lung tissue causing
a lung abscess as well.
Occasionally there are endemic break-outs of Klebsiella
pneumoniae in hospitals, which is another bacterium type that also can lead to
lung abscesses with complications (more about
pneumonia see this link). Here is a link to a simplified picture
of a lung abscess.
The patient usually is sick for several weeks or months
with a lack of appetite and the resulting weight loss. A chronic cough is usually
present, but may not be so in a debilitated elderly person.
With a smaller
abscess that drains well there might be only a low grade fever of 101.5°F (38.5°C).
However, in a patient where the abscess is larger and some of the toxins get into
the bood stream there would be a much more acute clinical picture with high temperatures
of 103°F (39.5°C) or higher. Most of the time the phlegm production is copius
and has a foul smell. The physician would detect certain signs such as dullness
to percussion in one area of the lung with diminished breath sounds over this
area using the stethoscope. In a chronic case where a lung abscess is not diagnosed
for several months a thickening of the fingers, called clubbed
fingers, can develop as a result of the chronic shortage of oxygen
in the tissues.
Blood tests usually
show an increase in the white blood cell count with a "shift to the left"
on a smear meaning that there are a lot of pus cells circulating in the blood
stream. In the early stages chest X-rays usually show an area of pneumonia with
subsequent development on repeat X-rays
of a lung cavity, which is due to the lung abscess. In this image
the white arrows point to the abscess cavity, the black arrow points to the fluid
level. CT scanning
may be required to get more details about the abscess cavity. Blood cultures may
be detecting the offending bacteria. Occasionally Entameba histolytica, a pathogen
in the gastrointestinal tract may cause a lung abscess and this or another pathogen
might be isolated from one of the phlegm (sputum) samples.
The best sample
usually is obtained early in the morning and the patient should be encouraged
to cough the sample right into a sterile container without mixing it with saliva.
Otherwise there is a danger that other anaerobic bacteria that are also contained
in the saliva would confuse the clinical picture. After treatment the bacteria
would be difficult to culture, so it is important to obtain as good a bacterial
diagnosis as is possible before treatment is begun. The clinician may decide to
do a transtracheal (through the windpipe) or transthoracic(through the chest wall)
biopsy to obtain an uncontaminated, pure bacterial sample for isolation
of the pathogen. Occasionally the clinical picture is not clear-cut and the lung
specialist may want to do a bronchoscopy to rule out a tuberculous lung cavity,
that may be mistaken for a lung abscess. Biopsy material and culture samples obtained
through this procedure, which has its own risk, can clarify the diagnosis and
ensure proper treatment.
Treatment consists mainly in
giving the appropriate antibiotic therapy. Initially this is given by the intravenous
route. Later when the patient is afebrile this can be switched to oral antibiotics.
However, it is important that the lung abscess is followed along with repeat imaging
studies until it is resolved completely.
This requires often a prolonged
antibiotic therapy for 2 to 4 months! This should be done under proper supervision
by a physician, preferably by a lung specialist. The choice of the antibiotic
is dictated by the culture results. Often the clinician might start the patient
on intravenous clindamycin intitally or a combination of penicillin G (or erythromycin)
with Flagyl until the culture report is back. At that point a switch to an antibiotic
that fits the culture report would be done, if necessary. The death rate of an
anaerobic lung abscess is about 15%, if Staphylococcus aureus or Klebsiellae pneumoniae
are involved, can be 30 to 50%. Occasionally there might be a case where the antibiotic
therapy does not resolve the lung abscess because of underlying lung diseases
such as a bronchictasis or an area of atelectasis that gets repeatedly infected.
In this case a referral to a thoracic surgeon night be necessary to get an opinion
whether surgery would help solve this problem. These cases are rare, but when
done in the appropriate patient, can be helpful.