ID: 55: FIBRILLARY GLOMERULONEPHRITIS:LOOKS LIKE AMYLOID BUT ITS NOT!

Introduction Fibrillary glomerulonephritis is a rare disorder with a prevalence of 1% in renal biopsies.The mean age of presentation is 50 years, proteinurea in 100%, nephrotic syndrome in 70–75%, renal insufficiency (Cr≥1.5) in 50–55%, hypertension 70% and hematuria in 70% cases.Etiology is unknown and diagnosis is established by pathognomonic electron microscopy findings. This case illustrates the presentation, workup and diagnosis of fibrillary glomerulonephritis (FGN). Case Description A 49 year-old-female with history of hypertension, obstructive sleep apnea,non-steroidal anti inflammatory drug use for chronic back pain presented with shortness of breath on exertion and bilateral lower extremity swelling. Vital signs showed temperature 35.6 C, heart rate 75/min, respiratory rate 21/min and blood pressure 112/68 mm Hg.She had mild respiratory distress, bilateral crackles at lung bases and bilateral +2 pedal edema on physical examination. Complete blood count showed hemoglobin 10.7 g/dl and normal white cell count. Complete metabolic panel showed creatinine 1.1 mg/dl, blood urea nitrogen 21 mg/dl, albumin 2.6 g/dl and normal electrolytes. Urinalysis showed pH 6.0,specific gravity 1.028,+4 proteinuria,+2 hematuria and no casts. 24hour urine collection showed 4.3 g/day nephrotic proteinuria. Lipid profile showed cholesterol 308 mg/dl and non-HDL cholesterol 246 mg/dl. Hepatitis C, HIV, Goodpasture Disease, Cryoglobulinemia, Systemic Lupus Erythematosus and other autoimmune diseases were ruled out by appropriate tests. Serum and urine protein electrophoresis were without M-spike but with high free Lambda (29.7 mg/dl) and Kappa chains (23.6 mg/dl). A diagnosis of nephrotic syndrome was made due to the presence of edema, proteinuria, hypoalbuminemia and hyperlipidemia. A renal biopsy was done to evaluate the etiology of nephrotic syndrome. Biopsy showed focal segmental and global glomerulosclerosis with mild to moderate interstitial fibrosis and tubular atrophy. Immunofluorescence showed staining of glomerular capillary walls and mesangium for IgG, kappa and lambda. Electron microscopy showed linear, non-branching fibrils in the mesangium that averaged 20 nm in width (11.7–28.6 nm).Congo red staining was negative. Discussion A study of 66 cases identified most common histologic patterns as mesangial, membranoproliferative, endocapillary proliferative, crescentic and necrotizing, membranous and diffuse sclerosing in order of likelihood.This case had focal segmental and global glomerulosclerosis that is a rare finding. In the same study immunofluorescence staining was positive for IgG in 100%, C3 in 92% and both kappa and lambda in 84% cases. This case also demonstrated positive staining for IgG, kappa and lambda. The pathognomonic finding is presence of fibrillary deposits in the mesangium and glomerular capillary walls distinct from amyloidosis.The size of fibrils ranges from 8–15 nm in Amyloid and 12–24 nm in FGN. IgG is usually monoclonal in AL Amyloid as compared to polyclonal in FGN. The characteristic difference from amyloid is absence of reaction to histochemical dyes like Congo Red and Thioflavin T in FGN. One third of FGN cases are associated with malignancy, monoclonal gammopathy and autoimmune disorders. In our case an extensive workup was negative for all these conditions. Angiotensin inhibitors (ACEI) are used if the glomerular filtration rate is normal and proteinuria is present,to control blood pressure and reduce disease progression. Evidence for use of steroids and immunosuppressants is based on uncontrolled studies with variable success.In our patient a limited trial of corticosteroids with mycophenolate resulted in some improvement in proteinuria alongwith ACEI.