A 61 year old man with past medical history of hypertension, diabetes and hepatitis B, who presented with nephrotic syndrome and microscopic hematuria. Serum creatinine was 3.1 mg/dL. ANA is positive. DsDNA is negative. Complements are within normal limits. 

• Rare: < 1% of native kidney biopsies

• Associated with malignancy, dysproteinemia, and autoimmune disease

• Proteinuria (100%)

• Hematuria (~ 50%)

• 40-50% progress to ESRD within 2-4 years

• 35-50% recur in kidney allografts

• Diffuse mesangial expansion by eosinophilic material

○ Usually Congo red (-) [may be (+)]

•  Several histologic patterns

○ Mesangial proliferation

○Membranoproliferative glomerulonephritis (GN)

○Crescents in ~ 25%

○Segmental &/or global glomerular scarring

• Immunofluorescence: IgG and C3 in mesangium and along GBM

○Usually IgG4, rarely IgM and IgA

○Usually κ = λ

• Electron microscopy: Nonbranching, randomly arranged fibrils

○Thicker than amyloid

○Average: 20 nm; range: 10-30 nm

• DNAJB9 immunohistochemistry (88-98% sensitivity)

• Tubular basement membrane TBM deposits by IF and EM (15%)

• Amyloidosis

• Single light chain or nonimmunoglobulin, smaller, fibrils 8-12 nm thick

• Rare cases of Congo red (+) fibrillary GP may represent concurrent amyloidosis

• Immunotactoid glomerulopathy (GP)

• Microtubular substructure of deposits larger (fibrils 30-50 nm thick)

• Usually (~ 80%) monotypic

• Often associated with underlying plasma cell dyscrasia

• Cryoglobulinemic GN

• Serum cryoglobulins present

• Membranoproliferative pattern of injury with pseudothrombi on light microscopy

• Strong IgM, not IgG4 dominant

• Fibronectin GP

• Mesangial and subendothelial deposition of PAS(+) material

• Negative immunofluorescence staining