Introduction to Diseases with Monoclonal Immunoglobulin Deposits



Introduction to Diseases with Monoclonal Immunoglobulin Deposits


Robert B. Colvin, MD








Diagnosis of diseases with monoclonal immunoglobulin deposits &/or substructure by EM is facilitated by following the path in this algorithm, which begins with whether the deposits are Congo red positive, followed by immunofluorescence (IF) for monotypic immunoglobulin chains (single light &/or heavy chain), equal staining of light chains (polyclonal) or no immunoglobulin staining. Electron microscopy is then used for assessment of the substructure. Immunotactoid and fibrillary GP sometimes have monotypic light chain (a). MIDD has either light chain, heavy chain, or both (b) and has no organized substructure. PGNMID usually, but not always, has amorphous deposits (c).


ETIOLOGY/PATHOGENESIS


Monoclonal Immunoglobulin



  • May be produced by malignant lymphoid or plasma cell neoplasm


Reactive (Benign Monoclonal Proliferation)



  • Some represent “monoclonal gammopathy of undetermined significance” (MGUS) without identifiable underlying neoplasm at time of renal biopsy


  • Some cases never have an identified neoplastic proliferation



    • These appear to be clonal, but not malignant


APPROACH


Light Microscopy



  • Quite variable appearances



    • Mimic membranoproliferative GN, acute GN, membranous GN (MIDD, type I cryo, PGNMID)


    • Mimic diabetes with nodular mesangial glomerulopathy (MIDD)


    • Tubulointerstitial disease may predominate (MIDD, cast nephropathy, light chain proximal tubulopathy)


Special Stains



  • Congo red stain essential to distinguish amyloidosis



    • Amyloidosis can be due to monoclonal immunoglobulin or other proteins


    • Thicker sections more sensitive


    • High-quality polarizing microscope more sensitive


Immunofluorescence



  • Stains for light chains essential to distinguish this group of diseases


  • Occasional forms show only heavy chain deposits


  • Some monotypic light chains truncated & stain poorly


Jul 7, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Introduction to Diseases with Monoclonal Immunoglobulin Deposits
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