|
 |
|
|
|
| |
|
Pulmonary Mycobacterium Avium-Intracellulare Infections in Women
|
- Mycobacterium avium-intracellulare complex (MAC) pulmonary
infection may be seen in elderly
women without underlying lung disease,
but diagnosis is often delayed due to lack of clinical
suspicion
- Chest x-ray findings include multiple nodules and bronchiectasis in the right middle lobe and
lingula
- Chest CT has greater sensitivity for detecting bronchiectasis and cavities and is superior to chest
x-ray for diagnosis
- Patients with the appropriate radiological findings should
undergo further evaluation with
microbiological studies, which may
include bronchoscopy and lung biopsy
|
Pulmonary
infections due to non-tuberculous mycobacteria (atypical mycobacteria)
are rare in the general population and are usually more indolent and
harder to treat compared to tuberculosis. These infections are most
commonly due to Mycobacterium avium or M. intracellulare, which are
indistinguishable by standard microbiological techniques and are
generally grouped together as Mycobacterium avium-intracellulare
complex (MAC). Pulmonary infections with MAC have been primarily
described in patients with underlying structural lung disease including
bronchiectasis and prior granulomatous disease, and also occur in
patients with underlying co-morbidities such as cystic fibrosis and
alpha-1 antitrypsin deficiency. Upper lobe cavitary disease with MAC
occurs primarily in older men with significant tobacco and alcohol
histories – most often in the setting of underlying chronic obstructive
lung disease. Though MAC can be detected in the respiratory tract of
patients with AIDS, isolated pulmonary infection with MAC in this
condition is actually rare.
MAC infections have also
been observed in a third group of patients without significant apparent
risk factors. About 90% are women over the age of 50 (most commonly
over 60), of lower body weight and non-smokers. Certain descriptive
studies have noted associations with mitral valve prolapse, pectus
excavatum, bronchiectasis and underlying reflux disease (GERD).
Clinically, these patients may present with a chronic cough and sputum
production and also may report recurrent sinopulmonary infections. They
are often treated initially with sequential antibiotics, without
long-term success.
Because MAC infection is not suspected in these patients, the diagnosis
is often delayed. However, this entity is not rare and about 30-50
cases requiring treatment are seen at MGH per year. Mycobacterial
studies must be specifically requested since routine bacteriological
cultures do not identify these organisms and they may require repeated
sampling to be identified.
MAC is ubiquitous in the environment and can be found in many water and
soil sources. Interpretation of microbiological data must be done in
the appropriate clinical, pathological and radiographic context, as it
is important to distinguish between contamination, colonization, and
infection. Therefore, imaging plays an important role in the diagnosis
of these patients and the criteria for diagnosis of MAC infection
includes certain radiographic findings on chest CT examination as well
as at least 3 repeated positive cultures or smears of sputum or
bronchial washes. In some cases, lung biopsy may be necessary to
confirm diagnosis.
|
|
Figure 2.
83 year old lady with a chronic cough. CT scan at the level of the
pulmonary artery demonstrates bronchiectasis (solid arrow)and
tree-in-bud nodules (dashed arrows) involving the middle lobe, lingula
and lower lobes, secondary to MAC
|
|
|
|
|
 |
Figure 1.
PA (1A) and Lateral chest (1B) radiographs in a 64 year old lady with a
chronic cough secondary to MAC. There is air space opacity in the
middle lobe (solid arrows) and lingula (dashed arrows)
|
Imaging of MAC Infection
Patients presenting with a chronic cough often receive chest
radiographs as an initial screening procedure. The chest x-ray may be
normal or demonstrate nodules, mild to moderate bronchiectasis,
air-space opacities, and atelectasis (Figure 1). The middle lobe and
lingula are most likely to be affected, with generalized disease in
severe cases.
If chest x-ray images show abnormalities suggestive of MAC infection or
if the symptoms persist with no apparent radiographic findings, it is
recommended that the patient be referred for further evaluation with
chest CT. Chest
CT findings of MAC are quite characteristic, comprised of
bronchiectasis, branching centrilobular nodules (“tree-in-bud”
abnormalities), cavities, air space disease, and atelectasis
predominantly in the middle lobe and lingula (Figures 2,3). In one
small series of symptomatic patients, CT findings of bronchiectasis and
multiple small nodules were reported to have a sensitivity of 80%,
specificity of 87%, and accuracy of 80% for the detection of MAC
infection.
Similar chest CT findings have also been
incidentally detected in asymptomatic patients, of whom 50% have no
detectable MAC bacilli by routine methods. Additional follow-up of
these patients via serial clinical, micro-biological and radiographic
monitoring is important, as it is often difficult to establish the
diagnosis of true pulmonary disease with MAC and to determine if and
when treatment is warranted.
|
|
|
|
|
Figure 3.
83 year old lady with a chronic cough. Coronal reformat CT scan through
the airways demonstrates extensive bronchiectasis, tree-in-bud nodules
(dashed arrow) and right upper lobe segmental atelectasis (solid arrow)
secondary to MAC
|
Patient Management and Follow-up
MAC infections are generally much more indolent than those due to M.
tuberculosis. Treatment requires combination drug therapy over a
prolonged period of time (12-18 months or longer) with cure rates of
only approximately 50-70% depending on the host and extent of the
disease. Drug tolerability is an important issue, and in some
series it is estimated that up to 20% of patients will have significant
difficulties tolerating anti-MAC therapy. If the disease is confined to
a small lung volume or if the patient has other life-threatening
conditions, the treating physician may opt to follow the patient with
serial CT and microbiological examinations and reassess periodically
the need for treatment. For those under treatment, close clinical
and radiographic monitoring are essential to assess for response and to
monitor for intolerance or toxicity of the combination
antimycobacterial therapy.
|
|
Scheduling
Chest radiography is performed on the main campus and at all off-campus
imaging facilities (Mass General West Imaging Waltham, Mass General
Imaging Chelsea, and MGH Revere Health Center). Chest CT imaging is
performed on the main campus, Mass General West Imaging Waltham, and
Mass General Imaging Chelsea. Both radiography and Chest CT may be
scheduled through Radiology Order Entry and Decision Support, http://mghroe
or by telephone (617-724-XRAY).
Further Information
For further questions, please contact Amita Sharma, M.D.
, Thoracic Radiology at 617-724-4254.
We would like to thank Dr. Sharma and Rocío Hurtado, M.D., Infectious
Disease Unit, for their assistance and advice for this issue.
This article provided useful information about the appropriate use of imaging studies:
Note: clicking one of these options will close this window. |
References
|
|
American Thoracic Society. (1997) Diagnosis and Treatment of Disease Caused by Nontuberculous Mycobacteria. Am J Respir Care Med 156: S1-25
Ellis, SM and Hansell, DM. (2002) Imaging of Non-tuberculous (Atypical) Mycobacterial Pulmonary Infection. Clin Radiol. 57: 661-9
Han, XY, Tarrand, JJ, Infante, R, Jacobson, KL and Truong, M. (2005) Clinical
significance and epidemiologic analyses of Mycobacterium avium and
Mycobacterium intracellulare among patients without AIDS. J Clin Microbiol. 43: 4407-12
Jeong, YJ, Lee, KS, Koh, WJ, Han, J, et al. (2004) Nontuberculous
mycobacterial pulmonary infection in immunocompetent patients:
comparison of thin-section CT and histopathologic findings. Radiology. 231: 880-6
Swensen, SJ, Hartman, TE and Williams, DE. (1994) Computed tomographic diagnosis of Mycobacterium avium-intracellulare complex in patients with bronchiectasis. Chest. 105: 49-52
Wittram, C and Weisbrod, GL. (2002) Mycobacterium avium complex lung disease in immunocompetent patients: radiography-CT correlation. Br J Radiol. 75: 340-4
|
|
|
|
|
|
|
|
|
