Diagnosis: Castleman Lymphadenopathy, Plasma Cell Variant
• The plasma cell variant of Castleman lymphadenopathy is characterized by paracortical plasmacytosis. The plasma cell variant can also share some features with the hyaline vascular variant in the form of follicles that show regressive changes with germinal center atrophy and hyalinization, increased hyalinized thick-walled vessels, which often penetrate a germinal center (lollipop lesion), and concentric layering of mantle zone cells (onion skin pattern).
• The plasma cell variant can be Kaposi sarcoma herpes virus/human herpes virus 8 (KSHV/HHV-8) negative or positive. The KSHV negative cases typically have plasmacytosis of mature morphology. In contrast, the KSHV positive cases typically have plasmacytosis that ranges from mature to immature or with plasmablastic morphology. In addition, the KSHV positive cases are more commonly seen in the setting of HIV infection.
• Rheumatoid lymphadenopathy is also associated with paracortical plasmacytosis and increased vascularity; however, rheumatoid lymphadenopathy is also associated with follicular hyperplasia where the follicles are large, irregularly shaped, and even coalescing. The follicles have an activated appearance with prominent germinal centers showing a “starry sky” appearance.
• Syphilis lymphadenitis is associated with paracortical plasmacytosis; however, syphilis lymphadenitis is also associated with follicular hyperplasia with follicles having a reactive appearance. The capsule is typically thickened and fibrotic and also cuffs the follicles in a scalloped type appearance. The capsule and capsular vessels show a lymphoplasmacytic infiltrate. Granulomas may be present.
• Marginal zone lymphoma with plasmacytic differentiation can show paracortical plasmacytosis. Typically, the paracortex would be expanded by lymphoma cells that may range from small round lymphocytes, monocytoid and plasmcytoid lymphocytes, to plasma cells; however, the follicles in marginal zone lymphoma would be enlarged and disrupted due to follicular colonization by the lymphoma cells.