Case 2 -

Fibrillary Glomerulonephritis David N. Howell, Duke Univ Med Ctr, Durham, NC

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Clinical History A 68-year-old Caucasian woman presented to an outside medical center with a two-month history of nausea and vomiting that had worsened over the past week. There was no associated abdominal pain, diarrhea, melena, hematemesis, or hematochezia. The patient had experienced a cough with subjective fever a few days previously, but denied hemoptysis. Her past medical history was notable for anemia, hypertension, breast cancer (status post lumpectomy), chronic kidney disease stage II, and hematuria of unclear duration. Urinalysis showed 3+ blood and 3+ protein; microscopic examination of the urine revealed numerous red and white blood cells as well as abundant bacteria and a moderate number of yeasts. The patient was felt to have a urinary tract infection, and was admitted to the hospital for hydration and therapy with antibiotic and antifungal agents. Her serum creatinine level increased from 2.4 mg/dL on admission to 3.9 mg/dL one week later, after which it trended downward. Hematuria and proteinuria persisted, however, and a percutaneous renal biopsy was performed to assess the cause. Pertinent Laboratory Data: Peripheral and cytoplasmic anti-neutrophil cytoplasmic antibody (pANCA and cANCA), anti-nuclear antibody (ANA), and anti-double-stranded DNA (dsDNA) all undetectable. No monoclonal protein detected by serum or urine protein electrophoresis. Serum complement levels (C3 and C4) within normal limits. No other serologic results available at the time of biopsy. Case 2 - Figure 1 albumin IF, 20x objective Case 2 - Figure 2 EM #1 Case 2 - Figure 3 EM #2 Case 2 - Figure 4 H&E #1, 4x objective Case 2 - Figure 5 H&E #2, 20x objective Case 2 - Figure 6 H&E #3, 20x objective Case 2 - Figure 7 IgG IF #1, 20x objective Case 2 - Figure 8 iGg IF #2, 20x objective Case 2 - Figure 9 Masson, 20x objective Case 2 - Figure 10 PAMS, 40x objective Introduction: Linear staining of glomerular capillary loop basement membranes for immunoglobulins and their components is encountered with considerable frequency in immunofluorescence microscopy of renal biopsies. This finding is a cardinal diagnostic feature of anti- glomerular basement membrane (anti-GBM) antibody glomerulonephritis (GN), and indeed, is often the sole biopsy finding that allows unequivocal distinction of this condition from other glomerulonephritides, particularly pauci-immune GN. Linear capillary loop staining patterns can be seen in a wide variety of other disorders, however, including diabetic nephropathy, light chain/monoclonal immunoglobulin deposition disease (LCDD/MIDD), immune complex glomerulonephritis, and fibrillary glomerulopathies. Electron microscopy (EM) is a valuable asset for distinguishing among these possibilities. The case provided for review illustrates this utility. The patient, a 69-year-old woman with a history of breast cancer, melanoma, and mild chronic kidney disease, presented to a referring hospital with hematuria and rapidly deteriorating renal function. Serologic studies were reportedly unrevealing, but did not include a test for circulating anti-GBM antibodies. A renal biopsy was performed. Pathological/Microscopic Findings and any Immunohistochemical or Other Studies: Light microscopic examination of the biopsy showed extensive chronic glomerular and interstitial changes, but also several cellular crescents. A Congo red stain was negative. Moderate linear immunofluorescent staining of capillary loops for IgG and immunoglobulin kappa and lambda light chains was seen, all in excess of staining for albumin. A diagnosis of anti-GBM antibody GN was entertained. Electron microscopy, however, showed diffuse infiltration of capillary loop basement membranes as well as mesangial areas by tangled fibrils, most measuring approximately 9-13 nm in diameter. Though this fibril size is more typical of amyloid than fibrillary GN, the polyclonal staining pattern of the deposits and their lack of congophilia favored the latter diagnosis. Differential Diagnoses: Anti-GBM antibody glomerulonephritis Diabetic nephropathy Light chain/monoclonal immunoglobulin deposition disease Immune complex glomerulonephritis Fibrillary glomerulonephritis Final Diagnosis: Fibrillary glomerulonephritis Case Discussion: In anti-GBM antibody GN, autoantibodies against the α3 chain of type IV collagen bind to the relevant antigen in capillary loop basement membranes and elicit an inflammatory cascade. Light microscopic examination of biopsy tissue typically shows glomerular tuft necrosis and crescent formation, which are often extensive; these changes can be subtle, however, particularly if the patient is biopsied early in the course of the disease or after presumptive therapy. Linear staining of capillary loop basement membranes for polyclonal IgG (i.e., IgG heavy chains along with both kappa and lambda light chains) is present and often intense; it is frequently preserved even in glomeruli with extensive acute or chronic damage. Of the conditions listed above, anti-GBM antibody GN is the only one without cardinal ultrastructural features; in most cases, if an intact glomerulus is imaged, only mild, nonspecific changes (patchy epithelial cell foot process effacement, mild thickening of basal lamina) are identified. In this setting, EM still provides pertinent negative information that helps to rule out the disorders discussed below. In diabetic nephropathy, the condition classically confused with anti-GBM antibody GN on immunofluorescent staining, excessive production of extracellular matrix material leads to expansion of mesangial matrix and thickening of capillary loop basement membranes, detected by light microscopy as diffuse and nodular glomerulosclerosis with relatively homogeneous but often subtle basement membrane thickening. Similar changes are typically seen in extraglomerular sites as well, including tubular basement membranes and small vasculature. Insudation of serum proteins, including immunoglobulins, into the abnormal basement membranes frequently occurs; here, the presence of antibody is a result rather than a cause of the damage. Linear immunofluorescent staining for polyclonal IgG similar to that seen in anti-GBM antibody GN is frequently seen. A key distinguishing feature is the concomitant presence of other insudated serum proteins, particularly albumin, for which staining intensity typically approximates that of IgG. By EM, diffuse thickening of capillary loop basement membranes and expansion of mesangial matrix in the absence of detectable deposits is typically seen; ultrastructural examination is a much more sensitive method of detecting basement membrane thickening than light microscopic evaluation. LCDD/MIDD are characterized by deposition of clonal immunoglobulin light chains, heavy chains, or whole immunoglobulin molecules within extracellular matrix, including mesangial matrix and glomerular and tubular basement membranes. The deposits stimulate production of new matrix/basement membrane material in a pattern that often mimics that of diabetic nephropathy, causing potential diagnostic confusion (particularly if it occurs in the setting of known diabetes). The immunofluorescent staining pattern in LCDD/MIDD is typically linear, but can usually be distinguished from the linear staining seen in anti-GBM antibody glomerulonephritis and diabetes by the clonal nature of the deposits. By EM, the deposits appear as finely granular electron-dense material within mesangial matrix and basement membranes; the finely particulate nature of the deposits presumably explains the homogeneity of their immunofluorescent staining. By both immunofluorescence and EM, the capillary loop basement membrane deposits are often relatively subtle compared with those in mesangial matrix and tubular basement membranes. Immune complex deposits usually have a granular appearance on immunofluorescence that parallels their ultrastructural morphology (see below). Occasionally, however, such deposits can have a linear staining quality. Thin, confluent subendothelial deposits in membranoproliferative glomerulonephritis (MPGN) type I often produce linear, scalloped capillary loop staining. In membranous glomerulonephritis, the deposits are occasionally either partially confluent or finely granular; in either situation, they can appear linear by immunofluorescence. Rare patients with membranous GN may have superimposed anti-GBM glomerulonephritis, further confusing the immunofluorescent picture. Though these disorders generally have distinctive light microscopic features, they can sometimes be confused with other entities; MPGN in a chronic phase, for example, has some histologic overlap with diabetic glomerulosclerosis. By EM, immune complex deposits are identified as clusters/clumps of extracellular, granular, electron-dense material, usually without identifiable substructure. Ultrastructural study reveals the precise location and distribution of the deposits, and is a vital tool both for establishing a diagnosis of immune complex GN and distinguishing between various types. Finally, linear immunofluorescent staining can be seen in glomerulopathies involving structured deposits containing immunoglobulins and their components, including AL amyloidosis and fibrillary glomerulonephritis. The light microscopic findings in these disorders are somewhat heterogeneous, particularly fibrillary GN, which can occasionally present with severe and acute glomerular injury including tuft necrosis and crescent formation. The deposits are often most prominent in the mesangium, but they sometimes infiltrate glomerular basement membranes in an insidious manner that leads to linear staining. In AL amyloidosis, the staining is for clonal kappa or lambda light chains; the deposits in fibrillary GN most commonly contain polyclonal IgG, though clonal variants occur. By EM, amyloid appears as tangled, non- branching fibrils that typically measure 8-10 nm in diameter. The fibrils in fibrillary glomerulonephritis are usually larger, averaging approximately 20 nm in diameter, but there is some variation and overlap with the size spectrum of amyloid fibrils. An additional distinguishing feature is that amyloid fibrils, by virtue of their extensive beta pleated sheet structure, bind histologic dyes such as Congo red and thioflavin T, while the fibrils of fibrillary GN do not react with these dyes. Conclusion(s): The case submitted for review is an example of fibrillary glomerulonephritis. In this case, EM provided crucial information that averted a misdiagnosis that could have led to unnecessary and possibly injurious therapy.