This is not a disease in itself but is an important feature of several kidney diseases. The main characteristics are:
- Marked proteinuria.
- Hypoalbuminemia.
- Generalised oedema.
- Hyperlipidemia.
When glomeruli are damaged,the permeability of the glomerular membrane is increased and plasma proteins pass through into the filtrate. Albumin is the main protein lost because it is the most common and is the smallest of the plasma proteins. When the daily loss exceeds the rate of production by the liver there is a significant fall in the total plasma protein level. The consequent low plasma ostomic pressure leads to widespread oedema and reduced plasma volume. This reduces the renal blood flow and stimulates the renin-angiotensin-aldoaterone system,causing increased reabsorption of water and sodium from the renal tubules. The reabsorbed water further reduces the osmotic pressure,increasing the oedema. The key factor is the loss of albumin across the glomerular membrane and as long as this continues,the vicious circle is perpetuates. Levels of nitrogenous waste products,ie,uric acid,urea and creatinine,usually remain normal. Hyperlipidemia,especially hypercholesterolemia, also occurs but the cause is unknown.
Nephrotic syndrome occurs in a number of diseases. In children the most common cause is minimal-change glomerulonephritis. In adults it may complicate:
- Most forms of glomerulophritis.
- Diabetic nephropathy.
- Systemic lupus erymatosus.
- Infections,eg.malaria,syphillis,hepatitis B.
- Drugs,eg.penicillamine.
