Glomerulonephritis, also known as glomerular nephritis, abbreviated GN, is a renal disease (usually of both kidneys) characterized by inflammation of the glomeruli, or small blood vessels in the kidneys. It may present with isolated hematuria and/or proteinuria (blood or protein in the urine); or as a nephrotic syndrome, a nephritic syndrome, acute renal failure, or chronic renal failure. They are categorized into several different pathological patterns, which are broadly grouped into non-proliferative or proliferative types. Diagnosing the pattern of GN is important because the outcome and treatment differs in different types. Primary causes are intrinsic to the kidney. Secondary causes are associated with certain infections (bacterial, viral or parasitic pathogens), drugs, systemic disorders (SLE, vasculitis), or diabetes.
 
Causes
The disease can be primary or secondary to liver and intestinal diseases. It also overlaps with Henoch-Schonlein purpura, a systemic renal disease in children in which similar IgA deposits occur.

Membranoproliferative/mesangiocapillary GN

This may be primary, or secondary to SLE, viral hepatitis, or hypocomplementemia. One sees 'hypercellular and hyperlobular' glomeruli due to proliferation of both cells and the matrix within the mesangium. Usually presents with a combined nephritic-nephrotic picture, with inevitable progression to end stage renal failure. The primary form consists of two types:

• Type 1 (Classical and Alternative Complement activation)
• Type 2 (also known as Dense Deposit Disease) Alternative Complement activation only. C3 Nephritic Factor stabilizes C3 convertase, leading to Hypocomplementemia. Unlike Type 1, no IgG is detected.

In both types, the basement membrane may develop a 'tram-track' appearance, due to duplication and splitting.

Rapidly progressive glomerulonephritis

Crescentic glomerulonephritis induced by infective endocarditis on PAS staining and immunofluorescence. PAS staining (left) demonstrated circumferential and cellular crescent formation with interstitial nephritis. Immunofluorescence (right) demonstrated C3 positive staining in mesangial area.
 
Rapidly progressive glomerulonephritis (Crescentic GN) has a poor prognosis, with rapid progression to kidney failure over weeks. Steroid therapy is sometimes used. Any of the above types of GN can be rapidly progressive. Additionally two further causes present as solely RPGN.

• One is Goodpasture syndrome, an autoimmune disease whereby antibodies are directed against basal membrane antigens found in the kidney and lungs. As well as kidney failure, patients have hemoptysis (cough up blood). High dose immunosuppression is required (intravenous methylprednisolone) and cyclophosphamide, plus plasmapheresis. Immunohistochemistry staining of tissue specimens shows linear IgG deposits.

• The second cause is vasculitic disorders such as Wegener granulomatosis and polyarteritis. There is a lack of immune deposits on staining, but blood tests are positive for ANCA antibody.

Signs and symptoms

• Most types of RPGN are characterized by severe and rapid loss of kidney function featuring severe hematuria (blood in the urine), red blood cell casts in the urine, and proteinuria (protein in the urine), sometimes exceeding 3 g protein/24 h, a range associated with nephrotic syndrome. Some patients also experience hypertension (high blood pressure) and edema. Severe disease is characterized by pronounced oliguria or anuria, which portends a poor prognosis.
• Serum analysis often aids in the diagnosis of a specific underlying disease. The presence of anti-GBM antibodies suggests type I RPGN; antinuclear antibodies (ANA) may support a diagnosis of systemic lupus erythematosus and type II RPGN; and type III and idiopathic RPGN are frequently associated with ANCA-positive serum.