CRITICAL REEVALUATION OF 41 CASES OF IDIOPATHIC CRESCENTIC GLOMERULONEPHRITIS

Despite the availability of different classifications for rapidly prog ressive glomerulonephritis (RPGN), patients with ''idiopathic crescent ic GN'' have not been yet inserted as a precisely defined subgroup, po inting to their probable heterogenicity. Trying to better define their characteristic, we retrospectively analyzed the clinical, histologica l and immunopathological features of 41 patients diagnostically labell ed ''idiopathic RPGN'' because they had no evidence of systemic diseas e (including systemic vasculitis), no anti-GBM mediated glomerulonephr itis and no clearly defined primary glomerulopathy. Starting by a thor ough morphological review, 2 subgroups were defined: group I (25 patie nts) with variable degrees of intraglomerular necrosis, and group II ( 16 patients) with no intracapillary necrotizing lesions. Group I showe d no or minimal endocapillary proliferation, intense interstitial infi ltrates with periglomerular localization, frequent ruptures of Bowman' s capsule and mild degree of glomerular and/or interstitial sclerosis. 16 patients in this group (64%) had irregular deposits of complement C3 at immunofluorescence while the remaining 9 (36%) had no immune dep osits. Clinically they had no previous history of preceeding urinary a bnormalities, had a mean of 1.8 g/day proteinuria and a positivity for ANCA in 92% (12/13). In group II there was frequently marked mesangia l proliferation, scarce interstitial infiltrates, no ruptures of Bowma n's capsule and marked degrees of glomerulosclerosis and interstitial fibrosis. All patients in this group had clearly defined immune deposi ts of C3 and/or IgG. Clinically 50% of these patients had a history of recurrent microhematuria and/or proteinuria, a mean:of 4.5 g/day prot einuria and negativity for ANCA in all 8 patients tested. Despite havi ng a comparable mean percentage of crescents and S. creatinine at the time of renal biopsy, both groups differed significantly in their resp onse to almost the same therapy, with 18 patients (72%) in group I sho wing remarkable improvement (> 50% decrease in their S. creatinine), w hile 9 patients (57%) in group II showed no response to therapy and pr ogressed to end-stage renal disease. We conclude that, ''idiopathic'' RPGN can be in fact the outcome of one of two pathogenetic mechanisms: the first is an acute necrotizing inflammation, with many features in common with the systemic vasculitides and actually represents a form of ''renal-limited'' vasculitis, while the other is the result of extr acapillary proliferation acutely complicating an underlaying primary c hronic glomerulopathy.