[A case of hypocomplementemic mesangial proliferative glomerulonephritis progressing to focal membranoproliferation without aggravation of urinalysis].

We reported a 14-year-old boy with hypocomplementemic mesangial proliferative glomerulonephritis progressing to focal membranoproliferation without aggravation of urinalysis. He was pointed out as having asymptomatic hematuria by a school urinalysis screening, and revealed mild hematuria and proteinuria (not nephrotic). The laboratory data showed severe hypocomplementemia and high titers of antistreptolysin O (ASO) and antistreptokinase (ASK). A renal biopsy specimen obtained 2 months after the onset showed diffuse mesangial proliferation, and did not display any characteristic changes in membranoproliferative glomerulonephritis by either light or electron microscopy. After eight months of observation, a second renal biopsy was performed in order to examine morphological changes, because severe hypocomplementemia, mild hematuria and proteinuria had persisted. The second biopsy specimen showed C3 deposition with a mesangiocapillary pattern detected by immunofluorescence microscopy and diffuse mesangial proliferation by light microscopy. In some glomeruli, electron microscopy showed focal mesangial interposition, which was considered to be a histological feature of focal membranoproliferative glomerulonephritis. Intravenous methylprednisolone pulse therapy and subsequent glucocorticoid administration (60 mg of prednisolone every other day) was performed. The serum complement level was elevated just after the methylprednisolone pulse therapy, but fell to the previous value within 2 months. The hypocomplementemia, even if proteinuria and hematuria were mild, indicated the existence of glomerular change in this case.