Glomerulonephritis

Glomerulonephritis, also known as glomerular nephritis, abbreviated GN', is a primary or secondary immune-mediated renal disease characterized by inflammation of the glomeruli, or small blood vessels in the kidneys. It may present with isolated hematuria and/or proteinuria (blood resp. protein in the urine); or as a nephrotic syndrome, a nephritic syndrome, acute renal failure, or chronic renal failure. They are categorised 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 one which are intrinsic to the kidney, whilst secondary causes are associated with certain infections (bacterial, viral or parasitic pathogens), drugs, systemic disorders (SLE, vasculitis) or cancers.

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Non Proliferative

This is characterised by low numbers of cells (lack of hypercellularity) in the glomeruli. They usually cause nephrotic syndrome. This includes the following types:

Minimal change GN

This form of GN causes 80% of nephrotic syndrome in children, but only 20% in adults. As the name indicates, there are no changes visible on simple light microscopy, but on electron microscopy there is fusion of podocytes (supportive cells in the glomerulus). Immunohistochemistry staining is negative. Treatment consists of supportive care for the massive fluid accumulation in the patients body (= oedema) and as well as steroids to halt the disease process (eg Prednisone 1 mg/ kg). Over 90% of children respond well to steroids, being essentially cured after 3 months of treatment. Adults have a lower response rate (80%). Failure to respond to steroids ('steroid resistant') or return of the disease when steroids are stopped ('steroid dependent') may require cytotoxic therapy (eg cyclosporin) which is associated with many side-effects.

Focal Segmental Glomerulosclerosis (FSGS)

FSGS may be primary or secondary to reflux nephropathy, Alport syndrome, heroin use or HIV. FSGS presents as a nephrotic syndrome with varying degrees of impaired renal function (seen as a rising serum creatinine, hypertension). As the name suggests, only certain foci of glomeruli within the kidney are affected, and then only a segment of an individual glomerulus. The pathological lesion is sclerosis (fibrosis)within the glomerulus and hyalinisation of the feeding arterioles, but no increase in the number of cells (hence non proliferative). The hyaline is an amorphous material, pink, homogeneous, resulting from combination of plasma proteins, increased mesangial matrix and collagen. Staining for antibodies and complement is essentially negative. Steroids are often tried but not shown to be effective. 50% of people with FSGS continue to have progressive deterioration of kidney function, ending in renal failure.

Membranous glomerulonephritis

Presents as nephrotic syndrome, leading cause in adults (35%). It is usually idiopathic, but may be associated with cancers (lung, bowel), infection (hepatitis, malaria), drugs (penicillamine), SLE. The basement membrane on which the glomerular cells sit is thickened, but no increase in cells. Immune staining shows diffuse granular uptake of IgG (immunoglobulin G). The basement membrane may completely surround the granular deposits, forming a "spike and dome" pattern. A third of people continue having the disease, 1/3 remit, 1/3 progress to end-stage kidney failure. As glomerulonephritis progresses (in any type), the tubules of the kidney (which are separate to the glomerulus) also become affected, showing atrophy and hyalinisation. The kidney grossly appears shrunken. Treatment with steroids is attempted if it is progressive.

Proliferative

This type is characterised by increased number of cells in the glomerulus (hypercellular). Usually present as a nephritic syndrome and usually progress to end-stage renal failure (ESRF) over weeks to years (depending on type).

IgA disease (Berger's nephropathy)

This is the most common type of glomerulonephritis in adults world-wide. It usually presents as macroscopic haematuria ( visibly bloody urine). It occasionally presents as a nephrotic syndrome. It often affects young males after an upper respiratory tract infection. Microscopic examination of biopsy specimens shows increased number of mesangial cells with increased matrix (the 'cement' which holds everything together). Immuno-staining is positive for immunoglobulin A deposits within the matrix. Prognosis is variable, 20% progress to ESRF. Steroids and immunosuppression are not effective treatments for this disease; ACE inhibitors are the mainstay of treatment.

Henoch-Schonlein purpura (HSP)

This is a systemic variant of IgA nephropathy which causes vasculitis of small vessels of which GN is a feature.

Post-infectious GN

Post-infectious glomerulonephritis occurs after Streptococcal infection - usually of the skin, after a latency of 10-14 days. This condition is essentially defined as an inflammation of the kidneys. Light microscopy shows diffuse hypercellularity due to proliferation of endothelial and mesangial cells, inflammatory infiltrate with neutrophils and with monocytes. The Bowman space is reduced (compressed), in severe cases might see cresent formation [see later]. However, biopsy is seldom done because the disease usually regresses. Patients present with a nephritic syndrome. Diagnosis is suggested by positive streptococcal titers in the blood (ASOT). Treatment is supportive, and the disease resolves (as a rule) in 2 weeks.

Mesangiocapillary GN

This is primary, or secondary to SLE, viral hepatitis, hypocomplementemia. One sees 'hypercellular and hyperlobular' glomeruli due to proliferation of both cells and the matrix within the mesangium. Presents usually with as a nephrotic syndrome but can be nephritic, with inevitable progression to ESRF.

Rapidly progressive GN (Crescentic GN)

As the name suggests, this type has a poor prognosis, with rapid progression to kidney failure over weeks. Any of the above types of GN can be rapidly progressive. Additionally two further causes present as solely RPGN. One is Goodpasture's syndrome, an autoimmune disease whereby antibodies are directed against antigens found in the kidney and lungs. As well as kidney failure, patient have hemoptysis (cough up blood). High dose immunosuprresion is required (intavenous Methylprednisolone) and cyclophosphamide, plus plasmapheresis. Immunohistochemistry staining of tissue specimens shows linear IgG deposits. The second cause is vasculitic disorders such as Wegener's granulomatosis and polyarteritis. There is a lack of immune deposits on staining, but blood tests are positive for ANCA antibody. Histopathology: The majority of glomeruli present "crescents". Formation of crescents is initiated by passage of fibrin into the Bowman space as a result of increased permeability of glomerular basement membrane. Fibrin stimulates the proliferation of parietal cells of Bowman capsule, and an influx of monocytes. Rapid growing and fibrosis of crescents compresses the capillary loops and decreases the Bowman space which leads to renal failure within weeks or months.

See also

• Nephritic syndrome
• nephritis

• Post-infectious glomerulonephritis - mayoclinic.com.

• Group A Streptococcal Infections - National Institute of Allergy and Infectious Diseases.