Systemic AL amyloidosis mimicking rheumatoid arthritis.

We report a patient with myeloma-associated systemic AL amyloidosis who showed chronic polyarthralgia as the main symptom. The clinical picture was similar to that of rheumatoid arthritis with regard to symmetrical swelling with tenderness in multiple joints, but inflammatory reactions were almost normal and autoantibodies were negative. He was diagnosed as having systemic AL amyloidosis based on deposition of kappa-light chain-immunoreactive amyloid in biopsied tissue and Bence Jones protein in serum and urine. Magnetic resonance imaging and bone scintigraphy suggested this disease as the cause of the polyarthralgia. Systemic AL amyloidosis may be important in the differential diagnosis of chronic polyarthralgia.