What is a nephrotic syndrome?
Nephrotic syndrome is defined by the following characteristics:
– proteinuria (loss of proteins into urine)
– hypo-albuminemia (decreased levels of the protein albumin in blood )
– edema (an accumulation of fluids in the body, which creates swelling)
– hyperlipidemia (an increased level of fats in blood)
Underlying mechanisms
Our blood is filtered by the kidneys. The kidney consists of millions of small “filtering units” (glomeruli). In these filtering units, waste products and water pass through the filter and flow into the urine, whereas the substances that are important to the body don’t pass the filter and remain in the blood. In the nephrotic syndrome this process is disrupted because of a leak in the glomeruli. This causes a loss of proteins into urine (proteinuria). Therefore too little of these proteins remain in the blood (hypo-albuminemia).
Loss of proteins leads to salt and fluid retention. This causes swelling of the body (edema).
Higher fat production by the liver and decreased fat degradation results in higher fat content in blood (hyperlipidemia).
Symptoms
A person with a nephrotic syndrome will have a swelling of the body (especially of the legs, belly and face). The person will urinate less and gain weight.
How common is it?
The nephrotic syndrome is rare and occurs in approximately 1-7 in 100,000 people a year.
Which forms are there?
There are several different types of nephrotic syndrome.
The nephrotic syndrome may be primary or secondary. A secondary nephrotic syndrome means that it is the result of another disease such as cancer, HIV-infection or diabetes. The most common types of primary nephrotic syndrome are the ‘minimal change nephropathy’ and the ‘focal segmental glomerulosclerosis’.
75% of children and 20% of adults with nephrotic syndrome have got a minimal change nephropathy. This means that a renal biopsy (this is the removing of a very small piece of the kidney to examine it with a microscope) shows only minor deviations in the glomeruli (kidney filters). This type of nephrotic syndrome can usually be successfully treated with medication (corticosteroids). In 60% of cases, however, there are one or more relapses of the disease, which require another treatment with corticosteroids. These relapses can be triggered for example by infections, vaccinations or stress.
A second form of nephrotic syndrome is due to focal and segmental glomerulosclerosis. In this form of nephrotic syndrome small scars are formed in the kidney filters (glomeruli). Because of these scars the glomeruli can no longer properly fulfill their function. This type of nephrotic syndrome is more difficult to treat and can lead to a complete loss of kidney function.
Depending on the severity and the clinical course of nephrotic syndrome, the disease can have a significant impact on a daily life of the patients and their families.
How is it diagnosed?
– Urine sample: The urinary protein level is measured and the urine is examined with a microscope.
– 24-hour urine collection: During 24 hours all urine is collected. The urinary protein loss during 24 hours is measured. To diagnose a nephrotic syndrome there must be a protein loss of more than 3.5 grams in 24 hours (in adults) and of more than 960 mg/m2 in 24 hours in children.
– Blood sample: On a blood sample hypo-albuminemia and hyperlipidemia can be determined and renal function can be measured.
– Renal biopsy: A kidney biopsy is the removing with a needle of a very small piece of the kidney. This piece is examined with a microscope to determine which type of nephrotic syndrome the patient has (for example minimal change nephropathy or focal segmental glomerulosclerosis). The renal biopsy can be performed by general or local anesthesia. A renal biopsy is mostly not necessary in children. Children with nephrotic syndrome are initially treated with corticosteroids. Only if this treatment fails, a kidney biopsy is indicated. In adults, a renal biopsy is usually required, because they have more frequently other types of nephrotic syndrome than the minimal change nephropathy.
Treatment
The nephrotic syndrome is initially treated with corticosteroids. If there are frequent relapses despite treatment with corticosteroids or if corticosteroids are insufficient, other drugs are used (cyclophosphamide, cyclosporine or mycophenolate mofetil). Currently, studies are being performed with levamisole. In some patients a combination therapy is required.
Supportive treatment of nephrotic syndrome consists of combating edema by limiting fluid intake, a diet with salt restriction and diuretic drugs.
Exceptionally it may be necessary to give an albumin infusion, to compensate the urinary albumin loss.
ACE-inhibitors are given to prevent the protein loss and to lower the blood pressure. Other antihypertensive drugs (drugs that lower the blood pressure) are sometimes used.
Only in a small minority of cases a nephrotic syndrome leads to irreversible loss of kidney function, wherefore dialysis or a kidney transplantation may be necessary.
