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Diagnosis: Fibrillary Glomerulonephritis

The average age for patients with fibrillary glomerulonephritis is about 50 years. The clinical presentation is generally proteinuria with or without associated nephrotic syndrome, sometimes accompanied by hematuria, hypertension, and some degree of renal functional impairment. The absence of congophilia represent a crucial feature of this disease that is very useful for diagnostic purposes. The disease occurs in older adults and is almost invariably localized to the kidneys. Fibrillary deposits have been reported rarely in the lungs, heart, and liver.

The light microscopic findings in this condition are quite variable. Most cases reveal mesangial expansion and some mesangial cell proliferation, whereas in other cases, mesangial deposition of eosinophilic material, difficult to differentiate from that seen in amyloidosis, represents the most noticeable finding. In most cases, there is also thickening of peripheral capillary walls, which may create confusion with a membranous nephropathy. The expanded mesangial areas are silver negative and a spicular arrangement similar to that described in amyloidosis may be seen. In most instances, the material replacing the mesangium is much more periodic acid– Schiff positive than amyloid. Approximately 15% to 20% of cases with fibrillary glomerulonephritis have crescents. Immunofluorescence reveals a classic pattern, with smudgy, ribbonlike to granular glomerular staining for IgG, C3, and κ and λ light chains (sometimes with light chain restriction) along peripheral capillary walls and in mesangium. If IgG typification is performed, IgG4 is dominant in most fibrillary glomerulonephritis cases. The overall fluorescence pattern is so characteristic that it should suggest the diagnosis. Fibrillary glomerulonephritis can be diagnosed with relative certainty when the light microscopic and the immunofluorescence findings are characteristic, as described above.

Ultrastructural examination identifies randomly disposed, 15- to 25-nm diameter fibrils in the mesangium, and frequently also along peripheral capillary walls. Rarely, fibrils also have been found in the interstitium, usually adjacent to tubular basement membranes. Infrequently, the typical fibrils described above coexist with microtubules that are of a diameter much smaller than those seen in most cases of immunotactoid glomerulopathy. The pathogenesis of this disorder has been a source of controversy over the years. It is believed that the fibrils occur because of polymerization of immune complexes, and possibly monoclonal light chains in some cases (From: Herrera GA, Turbat-Herrera EA. Renal diseases with organized deposits: an algorithmic approach to classification and clinicopathologic diagnosis. Arch Pathol Lab Med. 2010;134:512-31. [PubMed link]).

See the chapter: Amyloidosis... GN Fibrillary and other of our Tutorial.

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