Amyloid arthropathy resembling seronegative rheumatoid arthritis in a patient with IgD-kappa multiple myeloma.

A 67-year-old woman suffered from symmetrical polyarthralgia and multiple joint swelling simulating rheumatoid arthritis (RA). Laboratory examination showed negative results for rheumatoid factor, decreased levels of IgG, IgA, and IgM, and an increased level of IgD. Immunoelectrophoresis in her serum and urine revealed an IgD-kappa monoclonal component and Bence Jones protein (kappa), respectively. A bone marrow biopsy showed an excess of atypical plasma cells. A synovial biopsy revealed amyloid deposition composed of IgD-kappa. She was diagnosed with amyloid arthropathy (AmyA) secondary to IgD-kappa multiple myeloma. It is important to pay attention to AmyA due to multiple myeloma in patients with seronegative RA.