Renal involvement in essential mixed cryoglobulinemia

Essential mixed cryoglobulinemia (EMC) is infrequently recognized in this country. We report studies performed in six patients with EMC evaluated by us over the last 6 years. Purpura was present in three patients and glomerulonephritis in all. Two patients had chronic hepatitis B infection. Positive cryoglobulins and C1q binding, hypocomplementemia (especially low C4), positive rheumatoid factor titer, and negative anti-DNA antibodies were characteristic laboratory findings. The cryoprecipitate had strongly positive rheumatoid factor activity and contained a monoclonal IgM, kappa type in one of the two patients evaluated. The predominant lesion by renal biopsy was mesangiocapillary glomerulonephritis type I; electron microscopy revealed typical fibrillar structures in four cases. The above-mentioned features help distinguish EMC from other forms of glomerulonephritis.