Glomerulonephritis

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Glomerulonephritis (GN) is a term used to refer to several kidney diseases (usually affecting both kidneys). Many of the diseases are characterised by inflammation either of the glomeruli or of the small blood vessels in the kidneys, hence the name,^[1] but not all diseases necessarily have an inflammatory component.^{[citation needed]}

As it is not strictly a single disease, its presentation depends on the specific disease entity: it may present with isolated hematuria and/or proteinuria (blood or protein in the urine); or as a nephrotic syndrome, a nephritic syndrome, acute kidney injury, or chronic kidney disease.

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 differ 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 (

Signs and symptoms

Glomerulonephritis refers to an inflammation of the glomerulus, which is the unit involved in filtration in the kidney. This inflammation typically results in one or both of the nephrotic or nephritic syndromes.^[2]: 500

Nephrotic syndrome

The nephrotic syndrome is characterised by the finding of edema in a person with increased protein in the urine and decreased protein in the blood, with increased fat in the blood. Inflammation that affects the cells surrounding the glomerulus, podocytes, increases the permeability to proteins, resulting in an increase in excreted proteins. When the amount of proteins excreted in the urine exceeds the liver's ability to compensate, fewer proteins are detected in the blood – in particular albumin, which makes up the majority of circulating proteins. With decreased proteins in the blood, there is a decrease in the oncotic pressure of the blood. This results in edema, as the oncotic pressure in tissue remains the same. Although decreased intravascular oncotic (i.e. osmotic) pressure partially explains the patient's edema, more recent studies have shown that extensive sodium retention in the distal nephron (collecting duct) is the predominant cause of water retention and edema in the nephrotic syndrome.^[3] This is worsened by the secretion of the hormone aldosterone by the adrenal gland, which is secreted in response to the decrease in circulating blood and causes sodium and water retention. Hyperlipidemia is thought to be a result of the increased activity of the liver.^[4]: 549

Nephritic syndrome

The nephritic syndrome is characterised by

This is characterised by forms of glomerulonephritis in which the number of cells is not changed. These forms usually result in the nephrotic syndrome. Causes include:

Minimal change disease

Focal segmental glomerulosclerosis is characterised by a sclerosis of segments of some glomeruli. It is likely to present as a nephrotic syndrome. This form of glomerulonephritis may be associated with conditions such as HIV and heroin abuse, or inherited as Alport syndrome. The cause of about 20–30% of focal-segmental glomerulosclerosis is unknown. On microscopy, affected glomeruli may show an increase in hyalin, a pink and homogeneous material, fat cells, an increase in the mesangial matrix and collagen. Treatment may involve corticosteroids, but up to half of people with focal segmental glomerulonephritis continue to have progressive deterioration of kidney function, ending in kidney failure.^{[4]: 550–551}

Membranous glomerulonephritis

Microscopically, MGN is characterized by a thickened glomerular basement membrane without a hyperproliferation of the glomerular cells. Immunofluorescence demonstrates diffuse granular uptake of IgG. The basement membrane may completely surround the granular deposits, forming a "spike and dome" pattern. Tubules also display the symptoms of a typical Type III hypersensitivity reaction, which causes the endothelial cells to proliferate, which can be seen under a light microscope with a PAS stain.^[5]

Prognosis follows the rule of thirds: one-third remain with MGN indefinitely, one-third remit, and one-third progress to

Membranoproliferative GN (MPGN), also known as mesangiocapillary glomerulonephritis,

• Type 1 MPGN is caused by immune complex deposition in the mesangium and subendothelial space, typically secondary to
  systemic lupus erythematosus, hepatitis B and C, or other chronic or recurring infections. Circulating immune complexes may activate the complement system, leading to inflammation and an influx of inflammatory cells.^[4]
  ^{: 552–553}
• Type 2 MPGN, also known as Dense Deposit Disease, is characterised by an excessive activation of the complement system. The C3 Nephritic Factor autoantibody stabilizes C3-convertase, which may lead to an excessive activation of complement.^[4]: 553 Type 2 MPGN is a subgroup of C3 glomerulopathy, a newly proposed diagnosis which also encompasses C3 Glomerulonephritis (C3GN).^[7][8]
• Type 3 MPGN, which is caused by immune complex deposition in the subepithelial space.

Rapidly progressive glomerulonephritis

Rapidly progressive glomerulonephritis, also known as crescentic GN, is characterised by a rapid, progressive deterioration in kidney function. People with rapidly progressive glomerulonephritis may present with a nephritic syndrome. In management, steroid therapy is sometimes used, although the prognosis remains poor.^[9] Three main subtypes are recognised:^{[4]: 557–558}

• Type 1 is
  the coughing up of blood.^[4]: 557 High dose immunosuppression is required (intravenous methylprednisolone
  ) and cyclophosphamide, plus plasmapheresis. Immunohistochemistry staining of tissue specimens shows linear IgG deposits.
• Type 2 is characterised by immune-complex-mediated damage, and may be associated with
  systemic lupus erythematosus, post-infective glomerulonephritis, IgA nephropathy, and IgA vasculitis.^[4]
  ^: 558
• Type 3 rapidly progressive glomerulonephritis, also called pauciimmune type, is associated with causes of
  vascular inflammation including granulomatosis with polyangiitis (GPA) and microscopic polyangiitis. No immune deposits can be seen on staining, however blood tests may be positive for the ANCA antibody.^[4]
  ^{: 558–559}

Histopathologically, 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 endothelial 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 kidney failure within weeks or months. ^[citation needed]

Diagnosis

Some forms of glomerulonephritis are diagnosed clinically, based on findings on history and examination. Other tests may include:^[9]

• Urine examination
• Blood tests investigating the cause, including
  Anti-nuclear antibodies
  )
• Biopsy of the kidney
• Renal ultrasonography is useful for prognostic purposes in finding signs of chronic kidney disease, which however may be caused by many other diseases than glomerulonephritis.^[10]

Treatment

Antibiotic therapy to prevent streptococcal infection (prophylaxis). Steroids to suppress inflammation. Provide high calories & low protein, sodium & potassium diet. Monitor for sign of kidney failure, heart failure, and hypertensive encephalopathy.

See also

• Nephritic syndrome
• Nephritis
• Lupus nephritis
• Rapidly progressive glomerulonephritis

References