| Immunotactoid glomerulopathy
|
Key features:
 | Clinical: Commonly associated with B-cell lymphoproliferative disorders; often presents with nephrotic range proteinuria | | Light microscopy: Congo red-negative extracellular paraprotein deposition, usually with MPGN-like pattern of glomerular injury; mesangioproliferative or membranous patterns are less common | | Immunofluorescence: Monoclonal immunoglobulin reactivity (e.g., IgG/kappa) | | Electron microscopy: Parallel arrays of microtubules or fibrils, usually greater than 30 nm (10-90 nm) in diameter |
|
Definition:  | Immunotactoid glomerulopathy is a glomerular disease characterized by deposition of abnormal proteins (paraproteins) that are Congo red negative by light microscopy and show microtubular or fibrillary substructure by electron microscopy. The microtubules are usually greater than 30 nm in diameter, sometimes with central core, and are arranged parallel to the glomerular basement membranes. There is usually monoclonal immunoglobulin reactivity by immunofluorescence. Clinically, immunotactoid glomerulopathy is strongly associated with B-cell lymphoproliferative disorders. |
Synonym: | Paraprotein deposition disease |
Differential diagnosis:
Etiology: | Deposition of abnormal monoclonal protein in patients with paraproteinemia and lymphoproliferative disorder |
Clinical: | Usually occurs in patients over 60 years of age | | Usually presents with nephrotic range proteinuria; other presenting symptoms vary, from nephrotic syndrome, hematuria, acute renal failure, rapidly progressive nephritis, chronic renal insufficiency |
Histopathology: | Commonly, there is mesangial expansion with increased mononuclear inflammatory cells and matrix and peripheral capillary loop thickening (MPGN-like pattern of injury); rarely, the predominant pattern can be mesangioproliferative (if the deposition is not involving capillary loops) or, even less commonly, predominantly membranous | | Proliferative changes, such as increased endocapillary proliferation or crescent formation, can be seen on rare occasions | | Congo red stain is negative | | Silver stain may reveal “moth eaten” appearance (non-reactive deposits admixed with reactive matrix) |
Immunofluorescence:
Monoclonal (kappa or lambda) reactivity of immunoglobulins (usually IgG)
Click here to view table
Electron microscopy: | Visceral epithelial cells: Focal, sometimes marked effacement of visceral epithelial cell foot processes | | Glomerular basement membranes: Microtubular deposits, frequently in parallel arrangements, can be seen in subepithelial and intramembranous locations, extending to the paramesangial and mesangial compartment; the basement membrane can be affected with deposits in various degrees. The fibrils or microtubules are non-branching, usually greater than 30 nm (10-90 nm) in diameter | | Glomerular endothelial cells: Show loss of fenestrations and other non-specific changes; they do not contain tubuloreticular structures | | Mesangium: Usually expanded by matrix and organized microtubular deposits |
Clinical differential diagnosis: | Diseases that present with nephrotic syndrome (membranous nephropathy, amyloidosis, and idiopathic (primary) focal and segmental glomerulosclerosis) | | Diseases with acute renal failure and rapidly progressive nephritis (crescentic glomerulonephritides) |
Pathologic differential diagnosis: | Immune complex-mediated glomerulonephritides with MPGN pattern of injury; these include idiopathic MPGN, autoimmune diseases (such as lupus class IV, MCTD, RA, SS) and chronic infections (hepatitis B and C, hepatitis C-related cryoglobulinemia, endocarditis, shunt infections, parasitic infections) | | Fibrillary glomerulopathy | | Chronic thrombotic angiopathies | | Diabetic glomerulosclerosis | | IgA nephropathy | | Membranous glomerulopathy | | Lupus nephritis | | Postinfectious glomerulonephritis |
|  Please click here to comment | |
|
