C3 GN

C3 glomerulonephritis (C3GN) is defined as a GN whose pathogenesis implies an alteration in the alternative pathway of complement. In our patient, the initial clinical presentation was related to a previous infection of the respiratory tract, so it was logical to think in a post-infectious GN, however, the prolonged persistence of C3 hypocomplementemia suggested a complement alteration. Despite this, the patient continued without clinical or urinary abnormalities. When microhematuria was detected in a uroanalysis done a year later, the treating group decided to better document a possible persistent GN and ordered a biopsy. It is possible that not all nephrologists agreed, in this particular case and only for microhematuria, to perform renal biopsy. In this biopsy we found that C3 deposits were very evident in the IF, curiously mesangial. However, EM also documented subendothelial electron-dense deposits (Figure 10) that, although sparce, suggest an inflammatory process that also compromises capillary walls.

C3GN is a disease of relatively recent description, so we still need to know a lot about it. Most cases are described with a membranoproliferative GN pattern, however, we are increasingly aware of the great morphological and clinical variability of its presentation.

Given the large number of genetic and acquired alterations that can lead to the activation of the alternative complement pathway, it is expected that the clinical presentation and evolution will vary greatly. There will be cases of persistent GN with rapid evolution to chronic kidney damage, other cases will be more indolent and in other cases we may have periods of disease activity that intercalate with periods of quiescence. We hope in the near future to have much more knowledge about C3GN; for now we try to describe better its clinical and morphological variability.

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