Background/Purpose:

Anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN) is considered a “pauci-immune” disease, characterized by absent or mild glomerular tuft staining for immunoglobulin and/or complement. However, it is not unusual for renal biopsies in such cases to exhibit some immune complex (IC) deposition within glomeruli on immunofluorescence (IF) and/or electron microscopic study. Their potential pathologic and clinical significance is not clear, although a possible synergistic effect between immune complexes and ANCA in producing more severe glomerulonephritis is suggested by some authors. The aim of this study was to evaluate the prevalence and clinical significance of immune deposits in ANCA-associated pauci-immune GN.

Methods:

We included retrospectively all patients with biopsy-proven ANCA GN: granulomatosis with polyangiitis (GPA), granulomatosis with polyangiitis and eosinophilia (GPAE), microscopic polyangiitis (PAM) and renal limited vasculitis (RLV) between January 2002 and May 2013. Patients were divided into 2 groups: Group A: biopsy without IC deposits (less than 2+ intensity of immunostaining) and Group B: biopsy with IC deposits (more than 2+ intensity of immunostaining). IF included Ig (IgG, IgA and IgM) and complement components (C3 and C1q). Serum creatinine, estimated glomerular filtration rate (eGFR) at time of the biopsy, amount of proteinuria and hematuria, requirement of dialysis and extra renal involvement were recorded. 

Results:

Fifty-three patients (75.4% females) were included. The mean age at the time of the biopsy was 66.3 (SD: 14.3). Typical pauci-immune GN was found in 39 patients (73.5%, group A). In 14 patients (26.4%, group B) histopathological examination revealed substantial deposition of Ig or complement in the mesangium and/or along the glomerular capillary wall. IC deposition was more frequent in GPA and GPAE compared with PAM and RLV. C3 deposition on the capillary wall was the most frequent finding (64.2%), followed by C3 + IgG (21.4%) and IgG alone (14.2%). No patient presented positive staining for C1q. IgM and IgA were found only in two patients but along with C3. Compared with patients in group A, those in group B demonstrated significantly more 24 h proteinuria (mean 0.8 (SD: 7.6) vs 1.6 (SD: 10.7), p= 0.0036). No differences between groups were found related to age, gender, renal function, extra renal organ involvement at the time of biopsy, and in response to induction therapy (table 1).

Conclusion:

Our results confirm that in ANCA GN a substantial percentage of patients have evidence of Ig or C3 deposition in renal biopsies (26.4%). In this subgroup, IC deposition was associated with a significantly greater degree of proteinuria. Further clinical and basic research is needed to elucidate the significance of IC deposition in ANCA GN.

TABLE 1. DIFFERENCES BETWEEN THE GROUPS 

« Back to 2015 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/anca-associated-pauci-immune-glomerulonephritis-always-pauci-immune/