Childhood nephrotic syndrome

What is it?

Damage to the microscopic filtering units in the kidney called the glomeruli, causing loss of protein from the body, leads to the symptoms of nephrotic syndrome.

The glomeruli clean the blood and make urine. Normally, the glomeruli prevent the passage of protein from blood into urine, and in adults less than 150mg of protein is lost each day.

But in nephrotic syndrome, the glomeruli become leaky and more than 3.5g - that's 25 times the normal amount - of protein is passed out every 24 hours (the equivalent in children is 0.05g/kg body weight/24 hours).

Loss of protein leads to:

• Low levels of protein in the blood.
• Salt and water accumulating, leading to tissue swelling.

Who's affected?

Nephrotic syndrome can occur at any age but is particularly seen in childhood, especially between the ages of about two and eight. One in 5,000 people will develop nephrotic syndrome at some point in their life.

What causes it?

Nephrotic syndrome may be due to:

• Minimal change disease - although this is the commonest type of nephrotic syndrome in childhood, the exact cause is unknown. Biopsies of the kidney (tiny samples of tissue examined under the microscope) appear to be normal or very nearly so..
• Scarring of the glomeruli (seen in the biopsy in about 20 per cent of children) due to focal segmental glomerulosclerosis (FSGS), membranoproliferative glomerulonephritis, post-infectious glomerulonephritis or other conditions..
• Congenital nephrosis (an inherited kidney problem usually seen in small babies)..
• Henoch-Schonlein purpura.
• Allergic reactions, including allergy to medicines.
• Infections such as hepatitis B.
• Amyloidosis (a disease usually seen in people over 60).
• Diabetes (especially in later stages).
• Raised blood pressure (hypertension).

How's it diagnosed?

Nephrotic syndrome is usually fairly easy to diagnose, simply by measuring the amount of protein in the urine (it may be necessary to take urine samples over a 24-hour period to make these measurements).

The proportion of certain waste chemicals (such as creatinine or urea nitrogen) in the urine may show the extent of the damage to the kidneys. A kidney biopsy may be needed, especially in cases that don't respond to treatment.

Symptoms of nephrotic syndrome

• Swelling of the tissues around the eyes (called periorbital oedema) and in the abdomen, hands and legs (especially after long periods standing).
• Hypoalbuminuria (low levels of the protein albumin in the blood - this causes fluid to move from the blood into the tissues).
• High levels of cholesterol in the blood (hypercholesterolaemia, this occurs because enzymes normally involved in the metabolism of cholesterol also leak out of the kidneys) .
• Weight gain.
• Passing less urine.
• Passing urine less frequently.
• Urine that looks 'frothy'.
• Tiredness.
• Increased susceptibility to infections.
• Increased risk of thrombosis (formation of blood clots).

What's the treatment?

This depends on the type of underlying disease. Minimal change disease usually responds quickly to a short course of steroids and, although recovery may take several weeks, most children don't have any permanent kidney damage.

To reduce the swelling, the child's intake of fluid and salt may be restricted. Drugs, known as diuretics, that make the kidney produce more urine may also be given to help reduce swelling.

Occasionally, other medicines are given to prevent loss of protein, such as ACE inhibitors, which are usually used to treat high blood pressure.

In other types of nephrotic syndrome, steroids may be less effective and other medicines, such as powerful drugs that suppress the immune system (for example, cyclophosphamide, chlorambucil and cyclosporine) may also be needed.

Some types of nephrotic syndrome are very resistant to treatment.

Are there any complications?

Thrombosis and other blood clotting problems may occur and children may be particularly vulnerable to certain infections. In severe or prolonged cases the kidneys may fail and the person requires renal dialysis or even a transplant. For example, in FSGS one in three people gets progressively worse until their kidneys fail.

Although children with minimal change disease usually make a swift recovery, as many as one in three will go on to have frequent relapses throughout childhood, especially after a viral illness. Fortunately, these don't usually continue into adulthood.