Renal lesions in essential mixed IgG-IgM cryoglobulinemia. Study of 48 cases

56 renal biopsies in 48 patients affected by essential mixed IgG-IgM cryoglobulinemia have been examined by light microscopy and immunofluorescence. Patients were classified in four groups: 1) minimal lesions (4 patients); 2) pure proliferative mesangial lesions (9 patients); 3) membranoproliferative glomerulonephritis (23 patients); 4)proliferative glomerulonephritis with prominent intraluminal thrombi (12 patients). In this last group large intraluminal thrombi intensely fixing anti-IgG and IgM antisera were present; unlike the preceding groups, few deposits on capillary walls were seen. These four groups differed in renal clinical syndrome at presentation: in particular, proteinuria or nephrotic syndrome was the predominant manifestation in group 3, acute nephritic syndrome in group 4. In the latter, reversal of renal failure and regression of lesions could be observed. Various morphological aspects tend to show that in this disease more than one mechanism is operating in producing renal damage, including local trapping of abnormal circulating proteins.