Page 93 - AIDSBK23C

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large numbers of closely packed mycobacteria produce the striated appearance with
hematoxylin-eosin staining.[423]
The large macrophages are usually not accompanied by a typical granulomatous cellular
reaction. There may be occasional lymphocytes and epithelioid cells, but Langhans giant cells,
fibrosis, calcification, and caseous necrosis are quite uncommon. Rarely, the macrophages may
take on a spindle shape and form a mass lesion, typically in lymph nodes, known as a
mycobacterial "pseudotumor".[426] In many organs, the poorly formed MAC "granulomas"
consist only of single or small groups of macrophages that cannot be seen grossly and may not
be noticed until special stains are performed. Significant necrosis of surrounding tissues is
uncommon.[422]
Acid-fast bacilli (AFB) staining along with culture remains the standard procedure for
detection of MAC. The AFB stains commonly employed include the Ziehl-Neelsen and
Kinyoun carbolfuchsin methods. On acid fast staining, MAC organisms are not completely
distinctive from other mycobacteria, though they tend to be shorter than M tuberculosis and they
tend to be numerous. Culture is necessary for definitive identification. Diagnosis at autopsy is
aided by sampling several lymph node sites and by culture of enlarged nodes.[423]
Though MAC is often widespread throughout the body, few MAC-infected AIDS
patients die from this disease.[417] Organ failure from MAC leading to the immediate cause of
death most likely results from pulmonary involvement. Prophylaxis for MAC in both adults and
children with either azithromycin or clarithromycin may be considered when the CD4
lymphocyte count is <50/µL, though persons with active tuberculosis should be excluded
because of development of resistance to rifampin from treatment with rifabutin.[208]
In persons receiving antiretroviral therapy (ART) immune restoration disease (IRD) with
atypical features of MAC infection can occur. IRD with vigorous delayed-type hypersensitivity,
rather than anergy, results in more localized, rather than disseminated, disease. Lesions can
include lymphadenitis, pulmonary infiltrates or masses, pyomyositis, and subcutaneous
abscessing inflammation. Granulomatous to suppurative inflammatory responses are present.
Lesions may produce pain.[285]
Drug therapy for MAC infection may include clarithromycin, azithromycin, or rifabutin
and is most effective when combined with a second agent such as ethambutol, but a clinical
response may take two to eight weeks (Table 7). Combination drug therapy with additional
agents such as ciprofloxacin, clofazimine, amikacin, and rifampin show some effectiveness in
cases with more severe symptoms. AIDS patients infected with MAC require life-long
treatment. Resolution of mycobacteremia occurs more frequently and more rapidly with a three-
drug regimen of rifabutin, ethambutol, and clarithromycin. Rifabutin is also useful for
prophylaxis in patients with CD4 lymphocyte counts <100/µL. Many patients can still survive
for months with disseminated disease.[208,423,424,427]

MYCOBACTERIUM TUBERCULOSIS.-- Mycobacterium tuberculosis (MTB) occurs
commonly in many persons without AIDS, but the risk for MTB is substantially higher in
persons infected with HIV. The incidence of tuberculosis in persons with HIV infection is more
than 500 times that of the general population, and patients dually infected with HIV and latent
MTB progress to active tuberculosis at a rate of 8 to 10% per year.[428,429] Definitional criteria
for AIDS require laboratory evidence for HIV infection for inclusion of MTB as a disease
diagnostic of AIDS.[392] MTB is one of the most common causes of death in patients with
AIDS in Africa.[398]