[Fibrillary glomerulo-nephritis: a rare form of glomerular disease with organized deposits].

We describe the case of a 67 year-old female who presented weakness and fatigue. Laboratory data showed nephrotic level of proteinuria and dyslipidemia. A renal biopsy was performed, and studied by light microscopy, immuno-fluorescence and electron microscopy. Ultra-structural analysis revealed the existence of organized fibrillary deposits, straight and without ramifications, the thickness of which ranged from 15 to 20 nm. These fibres were identified, by light microscopy, as slightly nodular mesangial expansions PAS positive, Congo red negative and weakly positive for IgG. Given the above findings, the diagnosis was fibrillary glomerulonephritis. Glomerular lesions with organized deposits may exhibit syndromic and pathological overlap. For this reason it is important to initially discriminate between positive and negative Congo red deposits, using, in the latter case, transmission electron microscopy to distinguish between immuno-tactoid and fibrillary glomerulonephritis. This differentiation relies not only on ultrastructural features, but on different clinical characteristics. Unlike what happens with fibrillary glomerulonephritis, the immuno-tactoid shows a strong association with lymphoproliferative processes.