The prognostic significance of paraproteinaemia in rheumatoid arthritis

The incidence of lymphoma and myeloma are increased in rheumatoid arthritis (RA), although the reasons for this are incompletely understood. We have assessed the predictive value of monoclonal gammopathy in RA for the later development of lymphoproliferative malignancy. A serum paraprotein was discovered in 23 patients (14 female) with a median age of 59 years and a median duration of RA of 6 years. The paraprotein was quantified and further investigations including a bone marrow examination and skeletal survey were undertaken to investigate the possible development of a lymphoproliferative disorder. Secondary Sjogrenʹs Syndrome (SSS) was noted in 12 patients. The paraprotein was monoclonal in 21 patients and was classed as IgG (12 cases), IgA (6 cases) or IgM (3 cases). Biclonal paraproteins were seen in 2 patients. Free light chains were found in the urine of 8 patients. Bone-marrow abnormalities were found in 13 individuals. In two thirds of patients with either an IgA or an IgM paraprotein the bone marrow was abnormal, whereas less than half of those with an IgG paraprotein had an abnormal marrow. Patients were followed up for a median of 4 years and five patients with an abnormal bone marrow developed myeloma of whom 3 had an IgAλ paraprotein. Two other patients developed non-Hodgkins lymphoma. Extra-articular bony erosions were in 4 patients, three of whom developed myeloma but the presence of urinary free light chains was not specific for the development of malignancy. Paraproteinaemia in RA indicates monoclonal B cell proliferation and carries an increased risk of malignant trasformation.