A rare cause of subnephrotic proteinuria in an adolescent: Questions

Abstract

A 14-year-old boy presented with two weeks of petechial rash involving inner thighs, forearms, and ankles, with subnephrotic range proteinuria and microscopic hematuria. He had no preceding illness, nor arthralgias, abdominal pain, or unintentional weight loss; there was no family history of autoimmune or kidney disease. Physical examination was notable for obesity, mild hypertension (128/80), and mild pretibial edema with pitting. Faint pink macules were present along medial aspects of forearms, thighs, and ankles, which lacked the lacy appearance of vascuilitic rashes or pigmented remnants of Henoch-Schönlein purpura. Laboratory testing revealed a urine protein:creatinine ratio of 0.87 mg/ mg (normal < 0.2mg/mg), down from > 3.0 mg/mg present prior to referral. Complete blood count and plasma chemistries were within normal limits, including creatinine of 0.66mg/dL; albumin was in the low range of normal at 3.5 mg/dL. Urine microscopy revealed 5–10 RBCs per HPF, approximately 50% dysmorphic, with mixed cellular casts. Serologic evaluation revealed normocomplementemia, a positive ANA (1:320, speckled) and weakly positive anti-dsDNA, but extractable nuclear antibodies were negative. Kidney biopsy (Fig. 1) revealed glomeruli with eosinophilic material consistent with immune deposits segmentally distributed in mesangial and subepithelial regions of peripheral capillary loops, reminiscent of an atypical membranous nephropathy. One glomerulus was segmentally sclerosed, and there was focal tubular atrophy and interstitial fibrosis. Features of prominent inf l ammato ry ac t i v i t y— i nc lud ing endocap i l l a ry hypercellularity, necrosis, or crescents—were not present. Routine immunofluorescence performed on frozen tissue showed a disproportional degree of minimal glomerular capillary wall and mesangial staining for polyclonal IgG (0-trace) with somewhat greater degree of C3 (1+). There was no extra-glomerular staining, and other immunoreactants were negative. Electron microscopy showed widespread, occasionally large, nonorganized subepithelial and mesangial immune deposits. There were no subendothelial deposits or endothelial tubuloreticular inclusions.