IgM-IgG cryoglobulinaemia with IgM paraprotein component.

Four patients with mixed IgM–IgG cryoglobulinaemia are described. Clinically they all had some features of an autoimmune disease, while two of them had a lympho-epithelial tumour in the parotid gland. The mixed cryoglobulins of all patients contained an IgM paraprotein with the properties of a rheumatoid factor. They can be regarded as cryoprecipitates of a rheumatoid factor with autologous IgG. In one case the parotid tumour, and not the bone marrow, produced the IgM paraprotein. The clinical significance of the cryoglobulins is discussed. The IgM paraproteins with rheumatoid factor activity may be an expression of an underlying abnormality of the immunological system of these patients.