When Autoimmunity Masquerades as Plasma-Cell Dyscrasia: Castleman's Disease with POEMS Features in RA-Sjogren's Syndrome

Chronic autoimmune disorders such as rheumatoid arthritis (RA) and Sjogren's syndrome (SS) are marked by persistent immune activation and polyclonal B-cell proliferation. In rare instances, they may evolve into lymphoproliferative syndromes such as Castleman's disease (CD) or paraneoplastic entities like POEMS (Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal gammopathy, and Skin changes). Differentiating reactive plasmacytosis secondary to autoimmunity from plasma-cell dyscrasias is diagnostically challenging yet critical for management. We report a 54-year-old woman with seropositive RA and secondary SS who developed anemia, splenomegaly, and lymphadenopathy with a monoclonal IgG-? spike. Lymph-node histology revealed plasma-cell variant Castleman's disease, while bone-marrow evaluation and flow cytometry demonstrated polyclonal plasmacytosis without clonal restriction. The constellation of findings favored autoimmune-associated Castleman's disease with POEMS overlap. Recognition of such cytokine-driven reactive lymphoproliferation in autoimmune backgrounds is vital to prevent misdiagnosis as multiple myeloma and to direct appropriate immunomodulatory rather than cytotoxic therapy.