Nephrotic syndrome

Definition

Nephrotic syndrome is a collection of symptoms which occur because the tiny blood vessels (the glomeruli) in the kidney become leaky. This allows protein (normally never passed out in the urine) to leave the body in large amounts.

Description

The glomeruli (a single one is called a glomerulus) are tiny tufts of capillaries (the smallest type of blood vessels). Glomeruli are located in the kidneys, where they allow a certain amount of water and waste products to leave the blood, ultimately to be passed out of the body in the form of urine. Normally, proteins are unable to pass through the glomerular filter. Nephrotic syndrome, however, occurs when this filter becomes defective, allowing large quantities of protein to leave the blood circulation, and pass out or the body in the urine.

Patients with nephrotic syndrome are from all age groups, although in children there is an increased risk of the disorder between the ages of 18 months and four years. In children, boys are more frequently affected; in adults, the ratio of men to women is closer to equal.

Causes & symptoms

Nephrotic syndrome can be caused by a number of different diseases. The common mechanism which seems to cause damage involves the immune system. For some reason, the immune system seems to become 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 different 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 include diabetes, 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 heroine), allergic reactions (to insect stings, snake venom, and poison ivy), infections (malaria, various bacteria, hepatitis B, herpes zoster, and the virus which causes AIDS), and severe high blood pressure.

The first symptom of nephrotic syndrome is often foamy urine. As the syndrome progresses, swelling (edema) is noticed in the eyelids, hands, feet, knees, scrotum, and abdomen. The patient feels increasingly weak and fatigued. Appetite is greatly decreased. Over time, the loss of protein causes the muscles to become weak and small (called muscle wasting). The patient may note 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 will result in a generally malnourished state. Hair and nails become brittle, and growth is stunted. Bone becomes 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

Diagnosis is based first on the laboratory examination of the urine and the blood. While the urine will reveal significant quantities of protein, the blood will reveal abnormally low amounts of circulating proteins. Blood tests will also reveal a high level of cholesterol. In order to diagnose one of the kidney disorders which cause nephrotic syndrome, a small sample of the kidney (biopsy) will need to be removed for examination. This biopsy can be done with a long, very thin needle which is inserted through the skin under the ribs.

Treatment

Treatment depends on the underlying disorder which has caused nephrotic syndrome. Medications which dampen down the immune system are a mainstay of treatment. 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, heroine use, infections) which have led to nephrotic syndrome will often improve the symptoms of nephrotic syndrome as well. Some patients will require the use of specific medications to control high blood pressure. Occasionally, the quantity of fluid a patient is allowed to drink is restricted. Some patients benefit from the use of diuretics (which allow the kidney to produce more urine) to decrease swelling.

Prognosis

Prognosis depends on the underlying disorder. Minimal change disease has the best prognosis of all the kidney disorders, with 90% of all patients responding to treatment. Other types of kidney diseases have less 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 prognosis is very good.

Key Terms

Glomeruli

Tiny tufts of capillaries which carry blood within the kidneys. The blood is filtered by the glomeruli. The blood then continues through the circulatory system, but a certain amount of fluid and specific waste products are filtered out of the blood, to be removed from the body in the form of urine.

Immune system

The complex system within the body which serves to fight off harmful invaders, such as bacteria, viruses, fungi.

Kidney failure

The inability of the kidney to excrete toxic substances from the body.

Further Reading

For Your Information

Books

• Brady, Hugh R., et al. "Nephrotic Syndrome." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.
• Griffith, H.W. "Nephrotic Syndrome." In Instructions for Patients.Philadelphia: W.B. Saunders Company, 1994.
• Kaysen, G.A. "Nephrotic Syndrome: Nutritional Consequences and Dietary Management." In Nutrition and the Kidney, edited by W.E. Mitch, and S. Klahr. Boston: Little, Brown and Company, 1993.

  Periodicals

• Tune, B.M., and S.A. Mendoza. "Treatment of the Idiopathic Nephrotic Syndrome: Regimens and Outcomes in Children and Adults." Journal of the American Society of Nephrology, 8 (May 1997): 824+.

  Organizations

• American Kidney Fund. 6110 Executive Boulevard, Rockville, MD 20852. (800) 638-8299.
• National Kidney Foundation. 30 East 33rd Street, New York, NY 10016. (800) 622-9010.

Gale Encyclopedia of Medicine. Gale Research, 1999.