A 29-year-old man with treated HIV infection developed pancytopenia (white blood cell count, 3.9 × 10⁹/L; hemoglobin, 5.0 g/dL; and platelets, 11 × 10⁹/L). He had no skin lesions. His CD4 count was 239 cells/μL, serum interleukin-6 was 10 pg/mL (normal, <5 pg/mL), and HIV viral load was 251 000 copies/mL. A computed tomography scan showed extensive lytic bony lesions and diffuse lymphadenopathy. A bone marrow biopsy showed hypercellular marrow with sheets of spindle cell infiltrates and clusters of plasma cells (panels A-B; original magnification ×100 [A], ×500 [B], hematoxylin and eosin staining). There was no morphologic dysplasia. Immunostains revealed that the spindle cells were positive for human herpesvirus 8 (HHV8) (panel C, original magnification ×400, LANA-1) and D2-40 (panel D, original magnification ×400). CD138 (panel E, original magnification ×200) highlighted many clusters of plasma cells which were HHV8 negative and polytypic (panels F [kappa] and G [lambda]; original magnification ×500, immunohistochemistry stain). Flow cytometry confirmed no immunophenotypical evidence of myelodysplastic syndromes or lymphoma. A lymph node biopsy revealed Kaposi sarcoma, but not Castleman disease. Therefore, the pancytopenia is related to Kaposi sarcoma infiltration.

This interesting case demonstrates Kaposi sarcoma extensively involved in bone marrow. Although Kaposi sarcoma is not rare in patients with HIV infection, extensive bone marrow involvement, as seen in this case, is extremely rare. Clinical correlation and lymph node biopsy are needed for such patients to exclude HHV8-associated multicentric Castleman disease or lymphoma.