["Idiopathic" extracapillary glomerulonephritides without immune deposits are vascularitides: clinical and serologic analysis]

To determine the spectrum of systemic diseases potentially associated with pauci-immune rapidly progressive glomerulonephritis (GN), most of which being considered as idiopathic, we have analyzed extra-renal manifestations, occurrence of extra-glomerular vasculitis and incidence and specificity of ANCAs in 40 patients selected only on histological criteria. Extra-renal symptoms were unexpectedly observed in all patients but one, and were suggestive of vasculitis in 24 of them. Extra-glomerular vasculitis was evidenced in 18 kidney biopsies and four biopsies from other organs. Among the 33 patients with suspected or established vasculitis, 13 had presumed or biopsy-proven Wegener's granulomatosis (WG), three had a macroscopic form of polyarteritis nodosa and 17 had a clinical presentation compatible with the so-called microscopic polyarteritis previously described in the british literature. An additional patient had clinical signs of WG without clinical and histological evidence of vasculitis. ANCAs were detected in 28/33 and 25/34 sera tested by IF and ELISA, respectively: 19 contained anti-myeloperoxidase (MPO) antibodies and 6 had anti-proteinase 3 (Pr3) activity. Anti-MPO and anti-Pr3 antibodies were present in all clinical subgroups but with various incidences: anti-MPO antibodies were surprisingly more often detected (6/12) than anti-Pr3 (4/12) in patients with suspected or histologically proven WG but anti-Pr3 antibodies were nonetheless 3- to 4-fold more frequent in WG than in non-WG systemic vasculitis (1/12) and necrotizing CGN without evidence of extra-renal vasculitis (1/10). These results strongly suggest that pauci-immune necrotizing CGNs belong to the broad spectrum of necrotizing vasculitides affecting glomerular capillaries. This hypothesis is also supported by the good response of patients to immunosuppressive treatments known for their efficacy in vasculitides, whereas these treatments are usually less successful in severe forms of extra-capillary GN with immune deposits.