Paraproteins in rheumatoid arthritis and related disorders.

There is evidence that the prevalence of monoclonal parparoteinaemia is slightly increased in patients with rheumatoid arthritis. The possibility that this may be a marker of the development of later malignancy in such patients is explored. Mortality rates in rheumatoid arthritis are increased although the development of lymphoreticular malignancy contributes only a small percentage of this increase. However, it does seem likely that patients with longstanding severe rheumatoid arthritis are more at risk of developing myeloma or lymphoma if they have a monoclonal paraprotein band in their serum. IgA paraprotein seems to carry a higher risk than IgG whilst other factors such as urinary free light chains and the presence of secondary Sjögren's syndrome are of less prognostic significance. Similarly a monoclonal paraprotein may identify patients with primary Sjögren's syndrome who have a particular risk of later lymphoma whilst this risk does not appear to extend to patients with systemic lupus erythematosus. Patients with an overlap syndrome do not appear to be at greater risk than those with "pure disease". The association of other rheumatological disease and paraproteinaemia is briefly discussed.