Nephrotic syndrome is a collection of symptoms that occur because tiny filters (glomeruli) in the kidney become leaky. The glomeruli (a single one is called a glomerulus) are tufts of capillaries (the smallest type of blood vessels). They act as filters in the kidneys, allowing a certain amount of water andwaste products to leave the blood and eventually pass out of the body in theform of urine. Normally, proteins are unable to pass through the glomerularfilter. However, in people with nephrotic syndrome, this filter becomes defective, allowing large quantities of protein to leave the blood circulation andpass out of the body in the urine.
Patients with nephrotic syndrome are from all age groups, but children between 18 months and four years are at increased risk for the disorder. In children, boys are more frequently affected; in adults, the ratio of men to women iscloser to equal.
Nephrotic syndrome can be caused by a number of different diseases. Generally, the damage that results is due to immune system changes. For some reason, the immune system becomes directed against the person's own kidney. The glomeruli become increasingly leaky as various substances from the immune system are deposited within the kidney.
A number of kidney disorders are associated with nephrotic syndrome, including:
- Minimal change disease or MCD (responsible for about 80% of nephrotic syndrome in children, and about 20% in adults). MCD is a disorder of the glomeruli.
- Focal glomerulosclerosis
- Membranous glomerulopathy
- Membranoproliferative glomerulonephropathy.
Other types of diseases can also result in nephrotic syndrome. These includediabetes, sickle-cell anemia, amyloidosis, systemic lupus erythematosus, sarcoidosis, leukemia, lymphoma, cancer of the breast, colon, and stomach, reactions to drugs (including nonsteroidal anti-inflammatory drugs, lithium, and street heroin), allergic reactions (to insect stings, snake venom, and poison ivy), infections (malaria, various bacteria, hepatitis B, herpes zoster, and the virus that causes AIDS), and severe high blood pressure.
The first symptom of nephrotic syndrome is often foamy urine. As the syndromeprogresses, swelling (edema) develops in the eyelids, hands, feet, knees, scrotum, and abdomen. The patient feels increasingly weak and fatigued and loses appetite. Over time, the loss of protein causes the muscles to shrink and weaken (called muscle wasting). The patient may have abdominal pain and difficulty breathing. Because the kidneys are involved in blood pressure regulation, abnormally low or abnormally high blood pressure may develop.
Over time, the protein loss occurring in nephrotic syndrome results in general malnutrition. Hair and nails become brittle, and growth is stunted. Bones become weak, and the body begins to lose other important nutrients (sugar, potassium, calcium). Infection is a serious and frequent complication, as are disorders of blood clotting. Acute kidney failure may develop.
Diagnosis is based first on urine and blood tests. In people with nephrotic syndrome, the urine contains too much protein, while the blood has too little.Blood tests will also reveal a high level of cholesterol. In order to diagnose one of the kidney disorders that cause nephrotic syndrome, a small sample(biopsy) of the kidney is removed for examination. This biopsy can be done with a long, very thin needle which is inserted through the skin under the ribs.
The type of treatment for nephrotic syndrome depends on the type of disorderthat caused it. Medications that suppress the immune system are commonly used. The first choice is usually a steroid drug (such as prednisone). Some conditions may require even more potent medications, such as cyclophosphamide or cyclosporine. Treating the underlying conditions (lymphoma, cancers, heroin use, infections) that have led to nephrotic syndrome often improves the symptoms of nephrotic syndrome as well. Some patients will need medications to control high blood pressure. Occasionally, patients are told to limit the amount of fluid they drink. Swelling can sometimes be relieved with the use of diuretics, which allow the kidney to produce more urine and thus remove excess fluid from the body.
The success of treatment depends on the underlying disorder. Of all the kidney disorders, minimal change disease has the best treatment success, with 90%of all patients responding to treatment. Other types of kidney diseases haveless favorable outcomes, with high rates of progression to kidney failure. When nephrotic syndrome is caused by another, treatable disorder (infection, allergic or drug reaction), the likelihood of successful treatment is high.