An unusual case of loin pain and nephritis.

We report a 14-year-old girl with nephrotic syndrome and renal vein thrombosis (RVT) on initial presentation. The patient tested positive for antinuclear antibodies but only weakly positive for anti-double-stranded DNA (anti-dsDNA). Her C3 level was normal. Treatment with low molecular weight heparin resulted in resolution of RVT. Renal biopsy showed membranous glomerulonephritis with segmental sclerosis. Tissue immunostaining showed diffuse granular C3 and immunoglobulin (Ig)G staining along the capillary wall with focal segmental IgM staining deposits in the mesangium. No C1q, IgA, or fibrinogen was noted on immunofluorescence assay. With cyclosporin A and prednisolone, the patient went into remission and corticosteroids were tapered off gradually. Two years later, she had a relapse of proteinuria, hypocomplementemia, and extremely high anti-dsDNA. Systemic lupus erythematosus (SLE) was diagnosed, and she was promptly started on steroid and immunosuppressive agents, which resulted in reduction of proteinuria. Her renal function has been normal all along. Membranous nephropathy is uncommon in Chinese children and could be a possible early presentation of SLE.