"Catastrophic SLE" with Rosai-Dorfman sinus histiocytosis: successful treatment with anti-CD20/Rituximab

History and admission findings: A 59-year old woman was admitted with a fou r-month history of polyarthritis, myalgias and photosensitivity insufficien tly responsive to methotrexate, corticosteroids and azathioprin. On physica l examination she presented with symmetric ankle edema, polyserositis, pete chial bleeding and swelling of cervical, axillary and inguinal lymph nodes. Investigations: Laboratory analysis revealed a trilinear cytopenia without signs of hemolysis. Acute phase proteins were elevated. Furthermore antinuc lear antibodies, anti-phospholipid IgM antibodies, hypocomplementemia, a sp urious IgG kappa paraprotein were noted. CT scans confirmed lymphadenopathy and revealed a pleural and pericardial effusion. Bone marrow biopsy. showe d marked hypercellularity and polyclonal plasmocytosis. Based on these find ings systemic lupus erythematosus was initially suspected. However when abd ominal MRI showed a retroperitoneal mass, an extensive histological workup, which also included lymph nodes and spleen, revealed numerous plasma cells and histiocytes in dilated sinuses, diagnostic of Rosai-Dorfman sinus hist iocytosis. Treatment and course: High dose corticosteroids, intravenous gamma-globulin and repeated courses of cyclophosphamide failed to improve the pancytopeni a, as did splenectomy. The patient was given the anti-CD20 monoclonal antib ody Rituximab and all signs and symptoms improved dramatically. 18 months a fter the last treatment, the patient is in complete clinical and hematologi cal remission. Conclusions: Sinus histiocytosis of Rosai/Dorfman can be associated with or mimic severe SLE. Rituximab, an anti-CD20 monoclonal antibody, may improve the antibody-mediated pathogenetic mechanism underlying both entities.