Spindle cell tumors associated with mycobacteria in lymph nodes of HIV-positive patients 'Kaposi sarcoma with mycobacteria' and 'mycobacterial pseudotumor'

Patients infected with HIV often have unusual manifestations of common infe ctions and neoplasms. One such example is "mycobacterial pseudotumor," an e xuberant spindle cell lesion induced in lymph nodes by mycobacteria. Kaposi sarcoma also produces a spindle cell proliferation in lymph nodes of HIV-p ositive patients. These two entities must be differentiated from one anothe r because of differences in treatment and prognosis. We report here, howeve r, three cases of intranodal Kaposi sarcoma with simultaneous mycobacterial infection, the occurrence of which has not been clearly documented. For co mparison, we also studied three cases of mycobacterial pseudotumor, of whic h 14 cases have been described to date. There was considerable histologic o verlap between these two lesions. Acid-fast bacilli were present in all cas es, predominantly in the more epithelioid histiocytes in the cases of Kapos i sarcoma, and in spindle and epithelioid cells in the cases of mycobacteri al pseudotumor. The morphologic features that favored Kaposi sarcoma over m ycobacterial pseudotumor were the prominent fascicular arrangement of spind le cells and slitlike spaces, the lack of granular, acidophilic cytoplasm, and the presence of mitoses. Immunohistochemistry was a reliable adjunct st udy in the differential diagnosis, as the spindle cells in mycobacterial ps eudotumor were positive for S-100 protein and CD68 whereas those of Kaposi sarcoma wen CD31- and CD34-positive but negative for S-100 protein and CD68 , Awareness that Kaposi sarcoma may coexist with mycobacterial infection in the same biopsy specimen is important because these lesions may be misdiag nosed as mycobacterial pseudotumor. The clinical impact of distinguishing b etween Kaposi sarcoma with mycobacteria and mycobacterial pseudotumor is si gnificant because the presence of Kaposi sarcoma alters treatment and progn osis.