Recurrent and de novo glomerulonephritis in allografted kidneys: aspects of ultrastructural diagnosis.

Allograft glomerulonephritis (GN) is a noteworthy alternative in the differential diagnosis of renal graft dysfunction. The true frequency of allograft GN is unknown; a rough estimate is 5-15%. The highest rates of recurrence (100-20%) have been reported, in decreasing order of frequency, in mesangiocapillary GN (MCGN) type 2, IgA nephropathy, MCGN type 1, and focal segmental glomerulosclerosis (FSGS). In addition, in about 2% of allografts membranous GN (MGN) occurs as a de novo lesion. Electron microscopy has proved valuable in detecting early or mild MGN, MCGN type 2 and FSGS, and in differentiating between MCGN type 1 and allograft (rejection) glomerulopathy. Even with the aid of electron microscopy, however, the demarcation between MCGN type 1 and allograft glomerulopathy may prove impossible. The finding of prominent mesangial deposits (in an otherwise normal allograft), is highly suggestive of recurrent IgA nephropathy.