Histopathological findings of the bone marrow (A, B) and lymph nodes (C–E). (A) Hematoxylin and Eosin stain × 200. Bone marrow biopsy showed hypercellular marrow with increased numbers of megakaryocytes, including micro- and multi-separated nuclear megakaryocytes and megaloblastic change. (B) Silver stain × 200. Silver stain showed mild reticulin fibrosis. (C) Hematoxylin and Eosin stain × 200. A high-power field in the lymph node showed scattered lymphoid follicles with atrophic germinal centers, enlarged follicular dendritic cells, surrounding concentric rings of small lymphocytes, and penetrating vessels. (D) Hematoxylin and Eosin stain × 200. The interfollicular area was characterized by the proliferation of highly dense endothelial vessels and moderate numbers of mature plasma cells. (E) CD21 immunostain × 200. Immunostaining for CD21 showed tight/concentric and expanded/disrupted pattern of follicular dendritic cells. These findings were compatible with mixed-type Castleman’s disease.