Glomerular immune deposits are associated with increased proteinuria in patients with ANCA-associated crescentic nephritis

Background. In small vessel vasculitis and its renal-limited form, idiopathic crescentic glomerulonephritis, renal damage is characterized by pauci-immune necrotizing crescentic glomerulonephritis (CGN) without histological evidence of immunoglobulin (Ig) deposition. In some patients, however, significant amounts of immune deposits may be detected. Therefore, we evaluated the clinical significance of these immune deposits in anti-neutrophil cytoplasmic autoantibody (ANCA)-associated pauci-immune CGN. Methods. Renal biopsies of 45 consecutive patients with new onset of Wegener's granulomatosis' microscopic polyangiitis and idiopathic CGN were retrospectively evaluated by light microscopy, immunohistochemistry and electron microscopy and the findings compared with renal function and outcome. Results. Typical pauci-immune CGN was found in 37 patients (group I). In eight patients (18%; group II), however, histopathological examination revealed substantial deposition of Ig in the mesangium and/or along the glomerular basement membrane. Five of these eight patients were cANCA positive; two initially had pANCA and developed a cANCA pattern and one was pANCA positive. There were no differences between groups in age, gender, renal function or extrarenal organ involvement at the time of biopsy. However, patients in group II had significantly more proteinuria (5.4+/-3.1 vs 1.3+/-1.0 g/24 h; P=0.016). We also observed a trend for a worse outcome with respect to renal function and mortality in group II patients; however, the differences did not reach significance. Conclusions. Our results confirm that in ANCA-associated CGN a substantial percentage of patients have evidence of Ig deposition in renal biopsies. In this subgroup, Ig deposition was associated with a significantly greater degree of proteinuria. Further investigations are necessary to define the full clinical impact of immune-complex deposition on the clinical course of renal disease in pauci-immune CGN.