[Essential mixed cryoglobulinemia with kidney involvement].

Essential mixed cryoglobulin associated with rapidly progressive glomerulonephritis has been observed in a 64-year-old patient. The cryoglobulin consisted of monoclonal IgM-kappa and polyclonal IgG and displayed rheumatoid-factor activity. The antinuclear antibody test was negative. In the immunofluorescent method renal biopsy showed positive staining for IgG; IgM and the early and late complement components. The rheumatoid factor activity of the renal IgM deposits was demonstrated by binding of fluorescent aggregated IgG. There is thus evidence that the vasculitis observed in essential mixed cryoglobulin is caused by IgM-IgG complexes. The differentiation of essential mixed cryoglobulin from lupus nephritis with cryoglobulins is discussed.