Medullary Sponge Kidney

Definition

Medullary sponge kidney is a congenital defect of the kidneys where the kidneys fill with pools of urine.

Description

One of every 100 to 200 people have some form of this disease. The kidneys filter urine from the blood and direct it down tiny collecting tubes toward the ureters (ducts that carry urine from the kidney to the bladder). These tiny tubes gradually join together until they reach the renal pelvis, where the ureters begin. As the tubes join, they are supposed to get progressively bigger as they get fewer in number. In medullary sponge kidney, the tubes are irregular in diameter, forming pools of urine along the way. These pools encourage stone formation and infection.

Causes and symptoms

Although some cases of this disorder seem to be inherited, usually the cause is not known.

The symptoms associated with medullary sponge kidney are those related to infection and stone passage. Infection causes fever; back and flank pain; cloudy, frequent, and burning urine; and general discomfort. Stones cause pain in the flank or groin as they pass. They usually cause some bleeding. The bleeding may not be visible in the urine, but it is apparent under a microscope.

Diagnosis

Recurring kidney infections, bleeding, or stones will prompt x rays of the kidneys. The appearance of medullary sponge kidney on an intravenous pyelogram (x rays of the upper urinary system) is characteristic.

Treatment

Many people never have trouble with this disorder. For those that do, infections and stones will need periodic treatment. Infections should be treated with antibiotics early in order to prevent kidney damage. Stones may need to be surgically removed. Often, removal can be accomplished without an incision but rather by reaching up with instruments through the lower urinary tract to grab the stones. There is also a method of stone treatment called shock wave lithotripsy. A special machine delivers a focused blast of shock waves that breaks stones into sand so that they will pass out naturally. It is considered reasonably safe and usually effective.

Prognosis

Ignoring symptoms can result in progressive damage to the kidneys and ultimate kidney failure, but attentive early treatment will preserve kidney function.

Prevention

Diligent monitoring for infection at regular intervals and at the first symptom will give the best long-term results. By drinking extra liquids, most stones can be prevented. The most common kind of stones, calcium stones, can be deterred by regularly taking a medication that encourages urine production (thiazide diuretic).

BOOKS

Asplin, John R., and Frederic L. Coe. "Hereditary Tubular Disorders." In Harrison's Principles of Internal Medicine,ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

Martin, Thomas V., and R. Earnest Sosa. "Shock Wave Lithotripsy." In Campbell's Urology, ed. Patrick C. Walsh, et al. Philadelphia: W. B. Saunders Co., 1998.

PERIODICALS

Saklayen, M. G. "Medical Management of Nephrolithiasis." Medical Clinics of North America 81 (May 1997): 785-799.

ORGANIZATIONS

American Association of Kidney Patients. 100 S. Ashley Dr., #280, Tampa, FL 33602. (800) 749-2257. <http://www.aakp.org>.

American Kidney Foundation. 6110 Executive Boulevard, #1010, Rockville, Maryland 20852. 800-638-8299.

National Kidney Foundation. 30 East 33rd St., New York, NY 10016. (800) 622-9010.<http://www.kidney.org>.

J. Ricker Polsdorfer, MD

KEY TERMS

Congenital—Present at birth.

Intravenous pyelogram—X rays of the upper urinary system using a contrast agent that is excreted by the kidneys into the urine.

Thiazide diuretic—A particular class of medication that encourages urine production.