Co-existence of non-Hodgkin's lymphoma in the leukemic phase and polyarthritis simulating rheumatoid arthritis

The patient, a 64-year-old male, complained of morning stiffness, polyarthralgia and bilateral knee joint swelling with leukocytosis (24,200/microliter) in peripheral blood. The leukocyte differentiation revealed 54% medium-size immature lymphocytes. The majority of lymphocytes showed the B-cell characteristics of IgGk monoclonality, and CD19+ and CD20+ in cell surface phenotype, suggesting a B-cell malignancy, non-Hodgkin lymphoma in the leukemic phase. Arthropathy associated with lymphoid malignancy was suspected. However, the infiltrated leukocytes in the synovial fluid of the left knee joint were dominantly neutrophils and CD3+ T-cells, and compatible with the findings in rheumatoid arthritis (RA). The association of B-cell malignancy and RA is not frequently reported. We discuss the common underlying immunological abnormalities in both B-cell malignancy and RA.