Lymph nodes involved by multicentric Castleman disease among HIV-positive individuals are often involved by Kaposi sarcoma.

Multicentric Castleman disease (MCD), a lymphoproliferative disorder and Kaposi sarcoma (KS), a vascular tumor, both occur at a higher frequency among patients with human immunodeficiency virus (HIV) infection. Human herpes virus 8 (HHV8), with an ability to infect and persist in B-lymphoid cells and endothelial cells, is causally associated with both MCD and KS. The coexistence of these HHV8-associated diseases in the same tissue samples has hitherto not been investigated. In this report, we compile the histologic and immunohistochemical findings in 24 lymph node (LN) and 5 spleen samples from 26 patients documented to have HIV-associated MCD. In addition to MCD, 15 of 24 LN samples (63%) showed evidence of coexisting KS. The involvement by KS was typically "microscopic" and involved the LN capsule, trabeculae, or hilum. Examination of 5 spleens involved by MCD did not show any evidence of KS. These were compared with LN biopsies from HIV patients with neither granulomatous diseases, metastatic carcinomas nor lymphoproliferative disorders. Among 20 LN biopsies from 19 individuals without MCD, 5 LNs showed involvement by KS (25%); an association significantly lower than LNs with MCD (Pearson chi 2: 6.2, 2-sided significance: 0.013). Coexistence of MCD and KS in the same tissue sample is a common phenomenon and we hypothesise that the association is due to lytic HHV8 infection of B-lymphoid cells exposing susceptible endothelial cells at vulnerable subsites within the LNs to extremely high levels of HHV8 resulting in formation of KS tumorlets in MCD-LNs.