Durable remission of HIV-negative, Kaposi's sarcoma herpes virus-associated multicentric Castleman disease in patient with rheumatoid arthritis treated with methotrexate.

Multicentric Castleman disease (MCD) is a nonneoplastic lymphoproliferative disorder that has a poor prognosis. Optimal treatment is unknown. There are a few reported cases of MCD and rheumatoid arthritis. In this study, we report a patient with rheumatoid arthritis diagnosed with Kaposi's sarcoma herpesvirus-(KSHV, human herpesvirus-8) associated MCD that showed expression of viral IL-6. Treatment with methotrexate (MTX) resulted in a complete remission of her disease lasting for 54+ months. Multiple studies have suggested that MCD and rheumatoid arthritis are associated with overexpression of the growth-promoting cytokine interleukin-6 (IL-6), and that MTX downregulates the production of this cytokine in vivo. As such, we suggest that the dramatic improvement in this patient's disease is due to the immunomodulatory properties of MTX.