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A 38-year-old man was presented with nephrotic syndrome associated with hematuria and mild hypocomplementemia. Renal biopsy revealed lobular mesangial proliferation, thickened capillary walls, and intraluminal protein thrombi. Immunofluorescence showed marked and mild depositions of immunoglobulin (Ig) M heavy chains and complement C3, respectively, in a peripheral lobular pattern. On light chain staining, only kappa (κ) light and IgM heavy chains showed a similar pattern. Electron microscopy showed fine granular electrondense deposits in subendothelial areas and numerous globular deposits (varying size and density) in glomerular capillary lumens. Serum levels of Ig κ, but not of free κ, light chains were significantly increased. Bone marrow aspiration revealed a normocellular marrow. Waldenström's macroglobulinemia and cryoglobulinemia were ruled out. Clinically, steroid therapy was ineffective and proteinuria persisted. This report demonstrates that glomerular deposition of monoclonal IgM-κ can produce membranoproliferative- like changes in the glomeruli. This condition may be recognized as proliferative glomerulonephritis with monoclonal IgM deposits similar to the recently recognized proliferative glomerulonephritis with monoclonal IgG deposits.

Deposition of C3 without immunoglobulins ("isolated C3") was found in 9.8% of 540 renal biopsies performed between 1976 and 1982. Thirty-two of these samples were from patients with systemic diseases (16), well defined forms of glomerulonephritis (9), other renal diseases (4) or renal allografts (4). The remaining 22 patients are described. Five had nephrotic syndrome, three of them with minimal changes on light microscopy and good response to corticosteroids. We were left with a group of 17 patients who presented with gross (4) or microscopic (12) hematuria or asymptomatic proteinuria (1) whose biopsies showed mesangial proliferation or/and hyperplasia and who followed a benign course over the mean 3 years of follow-up, with the exception of one whose renal function is declining. This clinicopathological picture is similar to that described in two previous publications suggesting that "Isolated C3 mesangial proliferative nephritis" is a recognizable sub-group within the spectrum of glomerulonephritis.

Indications for renal biopsies in isolated hematuria in childhood remain difficult to define. Their limitation to patients presenting with either a macroscopic or a familial hematuria [Trachtman et al. 1984] bears the potential risk of missing the diagnosis of IgA-associated nephropathies (Berger disease and Henoch-Schönlein nephritis) which may manifest themselves by microscopic hematuria only. In order to reevaluate the association between biological IgA abnormalities and mesangial IgA deposits, iterative and concomitant determinations of IgA plasma levels, of IgA immune complexes and of IgA production by lymphocytes in vitro have been performed over a one-year period in two groups of hematuric children presenting with mesangial IgA deposits (14 cases) or not (13 cases). The incidence of positivity of each test was significantly higher in the former group of patients than in the latter. However, the best discrimination between both groups was observed when the three tests were repeated and/or considered together (97% vs 15% of positivity). In Berger disease and Henoch-Schönlein nephritis, IgA immune complexes were the only IgA abnormality more frequently detected in patients presenting with hematuria than in patients presenting with no hematuria at the time of testing. It is proposed to add IgA abnormalities to macroscopic or familial hematuria as indications for renal biopsies in isolated hematuria in childhood.