ANCA-associated pauci-immune glomerulonephritis: always pauci-immune?

OBJECTIVES

Anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN) is considered "pauci-immune" with absent or mild glomerular tuft staining for immunoglobulin (Ig) and/or complement. However, it is not unusual to see some immune deposits (ID) within glomeruli on immunofluorescence (IF). We determined to evaluate the prevalence and clinical significance of immune deposits in ANCA-associated GN.

METHODS

We included all patients with ANCA associated vasculitis with renal biopsies between January 2002 and May 2014: granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, microscopic polyangiitis and renal limited vasculitis. Patients were divided into Group A: biopsy without ID (≤2+ intensity of immunostaining) and Group B: biopsy with ID (>2+ intensity of immunostaining). 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. Mean age at biopsy was 66.3 years. Typical pauci-immune GN was found in 39 patients (73.5%, group A). In 14 patients (26.4%, group B) examination revealed substantial deposition of Ig or complement in the mesangium and/or along the glomerular capillary wall. The only difference comparing both groups was significantly higher proteinuria in group B (mean 1.6/24 h (SD: 10.7) vs. 0.8/24 h (SD: 7.6), p=0.0036).

CONCLUSIONS

In ANCA GN at least a quarter of patients were not "pauci-immune" (26.4%). In this subgroup, immune deposits were only associated with a significantly higher proteinuria. Further basic and clinical research is needed to elucidate the significance of immune deposition in ANCA GN.