Nutcracker syndrome in a child with familial Mediterranean fever (FMF) disease: renal ultrastructural features.

Renal nutcracker syndrome is an uncommon clinical condition caused by compression of the left renal vein. It is usually accompanied by hematuria and/or orthostatic proteinuria. To date, the pathogenic mechanism of proteinuria and its ultrastructural features have not been clearly identified. Here, we present the glomerular ultrastructural features of nutcracker syndrome and our attempt to analyze the relationship between proteinuria and ultrastructural features. Two months prior to admission, a 11-year-old girl with familial Mediterranean fever who was treated with colchicine was found to have proteinuria. Accompanying hematuria was not identified, and laboratory findings were otherwise normal. Doppler ultrasonography and computerized tomography angiography revealed an entrapment of the left renal vein. A kidney biopsy was performed due to the persistent proteinuria. Light microscopy revealed segmental, minimal increases in the mesangial cells and matrix. No amyloid deposition was present. Neither immunofluorescence nor electron microscopy showed immunoglobulin deposition. Increased thickness of the glomerular basement membrane due to the unequivocal radiolucent widening of the lamina rara interna was the most striking ultrastructural finding. At high magnification, there were no amyloidal fibrils. It has been proposed that hemodynamic alterations and structural changes in glomerular basement membrane glycosaminoglycans may play a role in the pathogenesis of proteinuria. Radiolucent expansion of the lamina rara interna of the glomerular basement membrane in the presenting case would seem to support these data.