Membranoproliferative Glomerulonephritis-Type I and Type II
In type I MPGN, light microscopy shows thickening of glomerular capillaries, accompanied by mesangial proliferation and obliteration of glomeruli.  With the electron microscope,  subendothelial deposits and growth of mesangium into capillary walls are demonstrable. Immunofluorescence studies show the presence of the C3 component of complement and,  rarely,  the presence of Ig.  The most common cause of MPGN type I is chronic hepatitis C virus infection.

This condition is usually associated with high levels of IgG/IgM.  Cryoimmunoglobulins may be present with normal or slightly reduced levels of complement.  There is no known effective treatment.

Type II MPGN is characterized by dense deposits visible by electron microscopy and lack of findings by immunofluorescence studies.  Treatment is unsatisfactory, and there is a high rate of recurrence after kidney transplantation.

Miscellaneous Diseases
Many medical illnesses that are metabolic,  autoimmune, or infectious, as well as neoplastic diseases and reactions to drugs and other toxic substances can produce glomerular disease.  These include diabetic glomerulopathy,  systemic lupus erythematosus, ANCA-positive renal disease (including Wegener’s granulomatosis), amyloid disease, multiple myeloma,  lymphomas,  carcinomas,  syphilis,  reaction to toxins, reaction to drugs (eg, trimethadione), and exposure to heavy metals.

A rare glomerular illness has been recently described with nephrotic syndrome:  fibrillary and immunotactoid glomerular nephritis. The lesions of fibrillary glomerulonephritis are characterized by randomly oriented fibril deposits 10-30 nm in diameter located within the mesangium and capillary wall. Immunotactoid glomerulopathy is characterized by deposits of microtubular structures of 18-19 nm and has been associated with lymphoproliferative disorders.

In contrast to amyloid,  the deposits in both diseases are Congo red-negative. Treatment is generally unsatisfactory.

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Flavio G. Vincenti, MD, & William J.C. Amend, Jr., MD

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