Page 143 - AIDSBK23C

Page 143

MYCOBACTERIOSIS.-- Mycobacterial pulmonary infections in AIDS are most
commonly caused by Mycobacterium tuberculosis, followed by Mycobacterium avium complex
(MAC). Other mycobacteria, including Mycobacterium kansasii and Mycobacterium fortuitum,
are seen infrequently. A presumptive diagnosis of pulmonary tuberculosis to satisfy definitional
criteria for AIDS can be made as follows:[392]

When bacteriologic confirmation is not available, other reports may verify cases of
pulmonary tuberculosis if the criteria of the Division of Tuberculosis Elimination,
National Center for Prevention Services, CDC, are used. A clinical case is defined when
the following criteria are met:

* A positive tuberculin skin test
* Other signs and symptoms compatible with tuberculosis, such as an abnormal,
unstable (worsening or improving) chest roentgenogram, or clinical evidence of
current disease
* Treatment with two or more antituberculous medications
* Completed diagnostic criteria

Laboratory criteria for diagnosis include:

* Isolation of M tuberculosis from a clinical specimen, or
* Demonstration of M tuberculosis from a clinical specimen by DNA probe or mycolic
acid pattern on high-pressure liquid chromatography, or
* Demonstration of acid-fast bacilli in a clinical specimen when a culture has not been
or cannot be obtained

Laboratory diagnosis of pulmonary tuberculosis in HIV-infected persons can be most
easily made with serum obtained for interferon-gamma release assay (IGRA). Sputum samples
can be obtained for detection of acid-fast bacilli under fluorescence microscopy with the
auramine stain. Specificity is high but sensitivity is not. Radiographic findings can aid in
diagnosis.[442] Other specimens may include bronchoalveolar lavage fluid, bronchial brushings,
and biopsies. The auramine stain can also be applied to tissue sections and viewed with
fluorescence microscopy and is more sensitive than the standard Ziehl-Neelsen acid-fast stain
viewed by light microscopy. Fine needle aspiration cytology can be employed and can detect
MTB in half of cases.[409]!
Radiographically, the findings of tuberculosis in AIDS patients with CD4 lymphocyte
counts above 200/µL are often similar to those of non-immunocompromised patients, with a
reactivation pattern that includes predominantly pulmonary involvement with nodular densities
and cavitation of larger nodules, but often in lower lobes, along with adenopathy and effusions.
In patients with CD4 lymphocyte counts below 200/µL there is likely to be a pattern of primary
tuberculosis with focal unilateral, often lower lobe, consolidation along with adenopathy, but
without cavitation. However, the chest radiograph may be normal in up to 15% of cases. The
lower the CD4 count, the more likely a miliary pattern may be present. An asymmetric
reticulonodular pattern on chest radiograph correlates with high resolution CT imaging that
shows adenopathy and a “tree-in-bud” pattern similar to bacterial bronchiolitis. When