Monoclonal rheumatoid factor (IgG λ). Its association with amyloid deposits containing λ light chains

A patient with monoclonal IgG λ rheumatoid factor was observed over a period of four years. During this time, serum level of the monoclonal protein fluctuated around 150 mg/dL and homogeneous λ light chains were present in the urine. The patient died of squamous-cell carcinoma of the lung and no evidence of multiple myeloma was present at the time of autopsy. However, the patient had systemic amyloidosis that affected primarily the blood vessels in most organs. Both the vascular and parenchymal amyloid deposits stained for λ light chains by the immunoperoxidase technique. These data support the hypothesis that amyloidogenic monoclonal immunoglobulins may be autoantibodies.