Page 144 - AIDSBK23C

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antitubercular therapy is begun along with antiretroviral therapy, there is often a worsening of
findings in the first month from increased inflammatory response with improved host immune
function. However, as immune status declines, the radiographic findings can also worsen.[607]
Mycobacterium tuberculosis will usually produce grossly recognizable tan to white firm
granulomas, often with caseation. Sometimes, the granulomas involve the pleura and are
associated with a hemorrhagic exudate or effusion. Microscopically, the classical features of
caseation with Langhans giant cells, fibrosis, and lymphocytic infiltration are present but not
pronounced. On acid fast stains, mycobacteria are scattered singly or in small clusters and can
be numerous and easy to demonstrate.[428,429]
In contrast, MAC is more likely to have significant extrapulmonary disease and produces
pronounced chest radiographic findings in about 5% of cases. If findings are present with
imaging, they are most likely to resemble those of MTB with areas of airspace consolidation and
diffuse patchy infiltrates with precominantly upper lobe involvement, along with mediastinal
lymphadenopathy. In immune restoration following antiretroviral therapy, mediastinal
lymphadenopathy may become prominent.[606,607]
Grossly visible granulomas are uncommon with MAC. The organisms are often found in
an interstitial distribution. Microscopically, granulomas are ill defined and consist primarily of a
single macrophage or small macrophage clusters. The macrophages have cytoplasm with a
striated pale blue appearance with hematoxylin-eosin staining. Acid-fast stains demonstrate
abundant mycobacteria within these macrophages.[423]
Mycobacterium fortuitum produces gross and microscopic patterns of pulmonary
involvement similar to M tuberculosis. Mycobacterium xenopi infections are not common but
may produce significant pulmonary disease late in the course of HIV infection.[445]
Infections with M kansasii tend to occur late in the course of AIDS, and radiographic
findings include interstitial and/or lobar infiltrates, with cavitation present in about 20% of cases.
Most patients present with fever, cough, chills, chest pain, weight loss, and dyspnea. Pulmonary
disease occurs in over 90% of cases, while disseminated disease is seen in a fifth of cases.
Thoracic lymph node involvement is common. Grossly there are variably sized granulomas
consisting of a large central area of noncaseating necrosis. Microscopically the granulomas have
extensive nuclear debris and neutrophils with a rim of epithelioid cells admixed with large
histiocytes with foamy cytoplasm or of fibrosis, but no multinucleated giant cells. Acid-fast
bacilli (AFB) are numerous, both within necrotic regions and within epithelioid cells. The long,
folded, beaded rod-shaped organisms are easily seen with Ziehl-Neelsen stain, but stain more
intensely and in greater numbers with the Fite stain. Most patients respond to therapy.[447,621]

COCCIDIOIDOMYCOSIS.-- Coccidioides immitis infection of the lungs is due to
inhalation of infective arthrospores with the subsequent development of proliferating
thick-walled spherules containing endospores. In AIDS, coccidioidomycosis is a rare cause of
pulmonary disease, even in endemic areas of the Southwestern United States. Pulmonary
infection in these patients probably results from reactivation of a previous, latent infection rather
than a de novo opportunistic infection. Clinical features are non-specific and include fever and
weight loss. An abnormal chest radiograph with diffuse infiltrates, single or multiple nodules,
cavitation, or hilar lymphadenopathy can be seen in about three-fourths of cases. Diagnosis
requires histologic examination with culture of bronchoalveolar lavage or lung biopsy.[620]
Grossly, small granulomas or patchy pneumonic consolidation may be seen.
Microscopically, the organisms are found in focal areas of interstitium. Large, thick-walled,