The patient was a 37-year-old white man receiving antiretroviral therapy for advanced human immunode- ficiency virus (HIV) infection. His latest CD4 lymphocyte count taken 3 months prior to presentation was 11 cells/ mm^sup 3^ (normal range, 495-1076 cells/mm^sup 3^). His past medical history revealed hepatitis C virus infection, genital gonorrhea, and chlamydial infection. At admission, he complained of a 2-week history of myalgias, abdominal pain at the left upper quadrant, and recent onset of diarrhea. He denied fever, chills, melena, or hematemesis. His laboratory studies showed a white blood cell count of 3.9 x 10^sup 9^/L (normal range, 4.5-10.5 x 10^sup ^9/L), hemoglobin level of 46 g/L (normal range, 140-175 g/L), and a hematocrit of 0.16 (normal range, 0.42-0.50).
An abdominal computed tomographic scan revealed prominent hepatosplenomegaly with hypodense areas in the spleen suggestive of contained splenic rupture. The patient underwent exploratory laparotomy. A diffuse enlargement of the intra-abdominal lymph nodes and marked splenomegaly were found. Total splenectomy with biopsy of a lymph node as well as prophylactic appendectomy were performed.
The spleen measured 17 X 12.5 x 9 cm and weighed 1295 g. The capsule was intact, but on cross-sectioning numerous irregularly shaped, randomly distributed, white nodules ranging in diameter from 0.2 to 0.4 cm were found throughout the congested parenchyma. Large, irregular, soft, pale areas ranging in diameter from 2.6 cm to 5.5 cm (Figure 1) were also observed. Sectioning of a single lymph node measuring 1 x 0.6 x 0.5 cm revealed a diffuse, homogeneous, yellow parenchyma. The vermiform appendix measured 7 cm in length and 0.5 cm on average diameter and was grossly unremarkable with a lumen patent up to the tip. A sample from the spleen was submitted for microbial culture.
Histologic evaluation of the spleen revealed multiple collections of histiocytes with abundant foamy and granular cytoplasm. Some of these collections resembled poorly formed granulomas with central necrosis (Figure 2). Special stains revealed numerous acid-fast (Figure 3) and periodic acid-Schiff-positive bacilli within macrophages. Ultrastructural evaluation showed that these bacilli resided inside large cytoplasmic vacuoles (Figure 4).
Evaluation of the lymph node showed complete replacement of the nodal architecture by a diffuse infiltrate of foamy and granular histiocytes. A diffuse infiltration of the appendiceal mucosa by histiocytes with similar histologic features was also found.
What is your diagnosis?
Pathologic Diagnosis: Disseminated Mycobacterium avium Complex Disease
The mycobacteria are small, weakly gram-positive bacilli with 2 distinctive features. The first is related to the presence of mycolic acid in the cell wall, which renders mycobacteria resistant to numerous antiseptic solutions and antibiotics.1 It also causes the retention of lipophilic stains even after acid-alcohol washes, hence the name acid-fast bacilli.1 The second feature is an unusually slow growth rate; it takes 3 to 4 weeks to obtain a visible colony on a plate,1 rendering classic microbiology inefficient in the management of disease.
Two species comprise the Mycobacterium avium complex (MAC), Mycobacterium avium and Mycobacterium intracellulare. There are about 30 serotypes of MAC organisms.1 Serotypes 1, 4, and 8 are the most commonly identified serotypes in patients with acquired immunodeficiency syndrome in the United States. Both M avium and M intracellulare are environmental saprophytes that survive well in soil, water, and food; the organisms are carried by animals as well.1,2
Mycobacterium avium complex causes 3 major clinical syndromes: disseminated disease, usually seen in persons with advanced HIV infection, and pulmonary disease and cervical lymphadenitis, which are usually seen in immunocompetent patients.2,3
The importance of MAC disease has increased in recent years with the increase in the number of patients with HIV infection.4 Disseminated MAC disease is the most common systemic bacterial infection in HIV-infected patients and the second most common opportunistic infection in this population.4 The risk of disseminated MAC disease increases with the severity of cell-mediated immunodeficiency. The incidence of MAC bacteremia ranges from 3% among subjects with CD4 cell counts between 100 and 199 cells/mm^sup 3^ to 39% among subjects with CD4 cell counts less than 10 cells/mm^sup 3^.4,5
The more common presenting manifestations of disseminated MAC disease include fever, night sweats, and weight loss of weeks to months duration. Generalized wasting, hepatosplenomegaly, and lymphadenopathy are the more common physical findings, albeit nonspecific. Anemia is the most common laboratory abnormality.2,3,5
Although it is widely believed that disseminated MAC disease results from reactivation of a latent infection, recent data suggest that the disease may develop from recent infection via the respiratory or gastrointestinal tract.6
In patients with advanced HIV infection, the intracellular growth of MAC appears to be uncontrolled.2 This could be explained in part by the in vitro observation that HIV envelope protein (gp120) reduces phagocytosis and enhances intracellular growth of MAC.5,6 It has been shown also that the intact HIV and the gp120 activate monocytes to express cytokines. Some of these cytokines, such as transforming growth factor-beta and interleukin (IL)-- 10, can inhibit the effects of tumor necrosis factor-alpha or granulocyte-macrophage colony-stimulating factor in augmenting intracellular MAC destruction by macrophages. Furthermore, other cytokines, such as IL-3, macrophage colony-stimulating factor, and IL-6, can directly promote intracellular growth of MAC organisms. In addition, HIV products may inhibit phagosome-lysosome fusion after phagocytosis of virulent MAC strains.2.6
Early in the course of infection or when there is relative preservation of the immune response, MAC may cause transient bacteremia and may not involve other tissues. As the suppression of the immune system becomes more severe, bacteremia becomes persistent and involvement of various organs and tissues becomes apparent. If left unchecked, MAC is capable of involving virtually any organ or tissue.2,5
Blood culture establishes the diagnosis in about 86% to 98% of cases. The preferred culture media involves lysis of peripheral blood leukocytes and inoculation onto solid media (eg, Lowenstein-Jensen, Middlebrook 7H11 agar) or into radiometric broth. The radiometric detection system allows identification of mycobacteria within 6 to 12 days, which is much more rapid than the 15 to 40 days required for solid media.1,3
The diagnosis of disseminated MAC disease also can be determined using biopsies of bone marrow, lymph node, or liver. The advantage of using biopsy specimens over blood cultures is that the biopsy may show acid-fast organisms or granulomas weeks before blood cultures are found to be positive. However, this histologic finding does not enable precise identification of the species of mycobacteria.2,3
A double-drug treatment including clarithromycin or azithromycin plus ethambutol is recommended. Once initiated, the therapy should be continued for the lifetime of the patient.
Chemoprophylaxis for patients with advanced HIV infection is recommended when the CD4 cell count is less than 50 cells/mm^sup 3^. Rifabutin, clarithromycin, or azithromycin plus rifabutin are all proven effective regimens.2,7
1. Inderlied CB, Nash KA. Microbiology and in vitro susceptibility testing. In: Korvick JA, Benson CA, eds. Mycobacterium avium-complex infection. New York, NY: Marcel Decker Inc; 1996:109-140. Lung Biology in Health and Disease; vol 87.
2. Chin DP, Hopewell PC. Mycobacterial complications of HIV infection. Clin Chest Med. 1996;17:697-711.
3. Wallace RJ, Glassroth J, Griffith DE, Olivier KN, Cook JL, Gordin F. Diagnosis and treatment of disease caused by nontuberculous mycobacteria. Am J Respir Crit Care Med. 1997;156:51 -525.
4. Horsburgh CR. Epidemiology of Mycobacterium avium complex disease: clinical challenges of Mycobacterium avium. Am J Med. 1997;102(5C, May suppl):1 1-15.
5. Burman WJ, Cohn DL. Clinical disease in human immunodeficiency virus-- infected persons. In: Korvick JA, Benson CA, eds. Mycobacterium avium-complex infection. New York, NY: Marcel Decker Inc; 1996:79-108. Lung Biology in Health and Disease; vol 87.
6. Shiratsuchi H, Ellner JJ, Johnson JL. Pathogenesis of mycobacterium avium-- complex infection in humans: interactions of monocytes and mycobacterium av- ium. In: Korvick JA, Benson CA, eds. Mycobacterium avium-complex infection. New York, NY: Marcel Decker Inc; 1996:163-195. Lung Biology in Health and Disease; vol 87.
7. Korvick JA, Benson CA. Advances in the treatment and prophylaxis of mycobacterium avium-complex in individuals infected with human immunodeficiency virus. In: Korvick JA, Benson CA, eds. Mycobacterium avium-complex infection. New York, NY: Marcel Decker Inc; 1996:241-262. Lung Biology in Health and Disease; vol 87.
Accepted for publication September 20, 2000.
From the Department of Pathology, The University of Texas Medical Branch, Galveston, Tex.
Reprints not available from the author.
Copyright College of American Pathologists May 2001
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