Rapidly progressive glomerulonephritis classification

Rapidly progressive glomerulonephritis is classified on the basis of cause of glomerular injury.The immunoflourescent microspcopic findings are used in determining the cause of glomerular injury.

RPGN is classified on the basis of the cause of glomerular injury and the findings from light and immunofluorescence microscopy.^[1][2].

• Type I RPGN is characterized by the presence of autoantibodies directed against the glomerular basement membrane (GBM)^[3].
• Type I also known as anti-GBM glomerulonephritis.
• The antibodies formed are known as anticollagen antibodies and react against type IV collagen of GBM.^[4]
• The antibodies can be produced by a stimulus such as viral URTI that exposes alveolar collagen membrane or it can be idiopathic.
• The antibodies formed can act against alveolar membrane and lungs get involved in some cases such as in goodpasture syndrome.

• Type II RPGN is caused by the deposition of immune complexes in the GBM.
• Immune complexes can be formed in certain infections or in connective tissue disorders.
• These immune complexes deposit over the GBM and activate the complement system resulting in crescent formation.
• Examples include:
• Postinfectious (staphylococci/streptococci)
• Connective tissue disorders
• Lupus nephritis
• Henoch-Schönlein purpura
• Immunoglobulin A nephropathy
• Mixed cryoglobulinemia
• Membranoproliferative glomerulonephritis

• Type III RPGN is also known as pauci immune RPGN^[4].
• There are no anti GBM antibodies or no immune complexes involved.
• It is further classified into 2 types:
  • Immunogenic – ANCA positive
  • Non immunogenic- ANCA negative/ Idiopathic
• ANCAs cause the release of lytic enzymes from neutrophils that damage the GBM.
• Systemic vasculitis is present in most of the cases but some occur without systemic involvement and only renal findings maybe present.
• Examples include
  • Granulomatosis with polyangiitis (Wegener granulomatosis)
  • Microscopic polyangiitis (MPA)
  • Renal-limited necrotizing crescentic glomerulonephritis (NCGN)
  • Eosinophilic granulomatosis with polyangiitis (EGPA; Churg-Strauss syndrome)
  • Drugs- hydralazine, allopurinol and rifampin.