genitourinary disorders
Membranoproliferative Glomerulonephritis
Introduction
Membranoproliferative glomerulonephritis (MPGN) is characterized by a pattern of glomerular injury on light microscopy, including hypercellularity and thickening of the glomerular basement membrane. The clinical presentation usually consists of mixed nephritic and nephrotic features. Cause is idiopathic or secondary to another disorder. Diagnosis is by renal biopsy. Treatment is directed at the underlying disorder, when present. For patients with idiopathic disease, treatment may be supportive or include corticosteroids and other immunosuppressive agents. (See also Overview of Nephrotic Syndrome .) Membranoproliferative glomerulonephritis (MPGN) is characterized histologically by glomerular basement membrane (GBM) thickening and proliferative changes on light microscopy. Historically, MPGN was classified into types I, II, and III, based on the location of deposits on electron microscopy examination: Type I: Characterized by electron-dense deposits in the mesangium and subendothelial space, consisting of both immunoglobulin and C3. Type II (dense deposit disease): Characterized by electron-dense ribbon-like deposits along the basement membranes of the glomeruli, tubules, and Bowman's capsule, consisting mostly of complement. Type III: Characterized by both subepithelial and subendothelial deposits. However, advances in the understanding of the pathogenesis of MPGN has revealed that the classification based on electron microscopy has limitations and can result in overlap among the different types. The preferred classification is based on pathophysiologic processes and informed by findings on immunofluorescence microscopy. This classification scheme broadly divides MPGN into Immunoglobulin/immune complex–mediated MPGN Complement-mediated MPGN MPGN without immunoglobulin or complement deposition An underlying (secondary) cause is present in the majority of cases regardless of type. Idiopathic (primary) cases are less common and usually observed within the immunoglobulin/immune complex–mediated category. Primary forms affect children and young adults between ages 8 and 30 and account for 10% of cases of nephrotic syndrome in children; secondary forms tend to affect adults>30. Men and women are affected equally. Reported familial cases of some types suggest genetic factors play a role in at least some cases. Many factors contribute to hypocomplementemia. 