Pattern of double glomerulopathies: a clinicopathologic study of superimposed glomerulonephritis on diabetic glomerulosclerosis.

Among 1715 renal biopsies investigated by means of light microscopy, immunofluorescence, and/or electron microscopy, 20 cases of various glomerulopathies (GP) were found to be superimposed on diabetic glomerulosclerosis (DGS). The most frequently superimposed GPs were acute GN (nine cases) and cryoglobulinemic GN (six cases). Although the former association is known to occur, the latter has not so far been reported. In the other patients DGS was associated with crescentic GN (two cases), membranoproliferative GN, membranous GN, and IgA nephropathy (one case each). Morphologic clues allowing the identification of the superimposed GP and the diagnostic relevance of the available morphologic methods were stressed. In particular, light microscopy was sufficient to identify the superimposed crescentic GN, whereas immunofluorescence and/or electron microscopy were needed in the other cases in order to show the composition and the seat of the deposits, respectively. In addition, electron microscopy was useful in identifying some peculiar features such as humps, mesangial cell interposition, and organized deposits in cryoglobulinemic GN. The actual frequency of superimposed GPs is difficult to assess: either under or overestimation is possible. Pathologists must be aware that this miscalculation is not an episodic event and that the estimation must be carefully sought whenever clinical data are equivocal and not fully fitting with DGS alone. The duration of the diabetes seems to favor the superimposition of GN on DGS. In these patients the prognosis is poor, not only when it could be expected to be, as in the cases with superimposition of crescentic or membranoproliferative GN, but also when DGS is associated with acute GN, whose prognosis is generally favorable.