Amyloid arthropathy mimicking seronegative rheumatoid arthritis in multiple myeloma: case reports and review of the literature.

We report two patients who suffered from symmetrical polyarthritis simulating rheumatoid arthritis. Acute phase response was almost within normal limits, and autoantibodies including rheumatoid factor were negative. Both of them were diagnosed as having amyloid arthropathy (AmyA) secondary to kappa multiple myeloma based on deposition of kappa-light chain-immunoreactive amyloid in biopsied tissue and Bence Jones protein in urine. Systemic AL amyloidosis may be important in the differential diagnosis of chronic polyarthralgia.