Polycystic kidney disease

Definition

Polycystic kidney disease (PKD) is an incurable disorder characterized by the formation of several or many fluid-filled cysts that:

• Replace healthy kidney tissue
• Enlarge the kidneys and impair their function
• Often cause kidney failure.

PKD is almost always inherited. In about 10 of every 100 cases, the disease is caused by a defective gene that is not inherited.

Description

The most common of all life-threatening, genetic diseases, PKD affects at least two of every 10,000 people. A child who inherits the PKD gene from either parent has a 50% chance of developing the disease.

A healthy kidney is about the same size as a human fist. PKD cysts, which can be as small as the head of a pin or as large as a grapefruit, can expand the kidneys until each one is bigger than a football and weighs as much as 38 pounds.

Types of PKD

Babies born with infantile PKD are often born dead. Few of these children survive for more than two years, and many of them die in infancy.

PKD is much more common in adults than in children. Symptoms usually start to appear between the ages of 30-50, and, though organ deterioration progresses more slowly than it does in children, untreated disease eventually causes kidney failure.

Complications of PKD

PKD cysts damage the kidneys' ability to filter waste products from the blood. They can also squeeze blood vessels, causing chronic high blood pressure that is hard to control.

As many as 50% of patients who have PKD have cysts on the liver, as well as on the kidneys. Other health problems associated with PKD include:

• Anemia
• Brain aneurysm
• Chronic leg or back pain
• Diverticular disease
• Enlarged heart
• Frequent infections
• Groin or abdominal hernias
• Kidney stones
• Mitral valve prolapse (displacement of the valve that prevents blood from backing up into the heart)
• Overproduction of red blood cells
• Pancreatic cysts.

A baby born with PKD has floppy, low-set ears, a pointed nose and small chin, and folds of skin surrounding the eyes. Large, rigid masses can be felt on both flanks, and the baby usually has trouble breathing.

Adults may experience only vague symptoms, like high blood pressure, frequent urination, and urinary tract infections, until they reach their 30s or 40s. Then they begin to develop back pain, abdominal swelling and tenderness, and other symptoms caused by kidney enlargement.

Other symptoms of PKD include:

• Blood in the urine
• Drowsiness
• Joint pain
• Menstrual pain
• Nail abnormalities.

Diagnosis

Many patients who have PKD don't have any symptoms. Their condition may not be discovered unless tests that detect it are performed for other reasons.

When symptoms of PKD are present, the diagnostic procedure begins with a family medical history and physical examination of the patient. If several family members have PKD, there is a strong likelihood that the patient has it too. If the disease is advanced, the doctor will be able to feel the patient's enlarged kidneys. Heart murmur, high blood pressure, and other signs of cardiac impairment can also be detected.

Urinalysis and creatine clearance tests can indicate how effectively the kidneys are functioning. Scanning procedures using intravenous dye reveal kidney enlargement or deformity and scarring caused by cysts. Ultrasound and computed tomography scans (CT) can reveal kidney enlargement and the cysts that caused it. CT scans can highlight cyst-damaged areas of the kidneys.

Treatment

There is no way to prevent cysts from forming or becoming enlarged, or to prevent PKD from progressing to kidney failure. Treatment goals include:

• Preserving healthy kidney tissue
• Controlling symptoms
• Preventing infection and other complications.

If adult PKD is diagnosed before symptoms become evident, urinalysis and other diagnostic tests are performed at six-week intervals to monitor the patient's health status. If results indicate the presence of infection or another PKD-related health problem:

• Aggressive antibiotic therapy is initiated to prevent inflammation that can accelerate disease progression.
• Iron supplements or infusion of red blood cells are used to treat anemia.
• Surgery may be needed to drain cysts that bleed, cause pain, have become infected, or interfere with normal kidney function.

Lowering high blood pressure can slow loss of kidney function. Blood-pressure control, which is the cornerstone of PKD treatment, is difficult to achieve. Therapy may include:

• Antihypertensives
• Diuretic medications
• Low-salt diet.

As kidney function declines, some patients need dialysis or a kidney transplant. Some patients need both types of treatment.

Prognosis

There is no known cure for PKD. In adults, untreated disease can be rapidly fatal or continue to progress slowly, even after symptoms of kidney failure appear. About half of all adults who develop PKD also develop kidney failure. Unless the patient undergoes dialysis or has a kidney transplant, this condition usually causes death within four years.

Although medical treatment can temporarily alleviate symptoms of PKD, the expanding cysts continue to increase pressure on the kidneys. Kidney failure and uremic poisoning (accumulation of waste products the body is unable to eliminate) generally causes death about 10 years after symptoms first appear.

On the horizon

Medications used to fight cancer and reduce elevated cholesterol levels have slowed the advance of PKD in laboratory animals. They may soon be used to treat adults and children who have the disease. Researchers are also evaluating the potential benefits of anti-inflammatory drugs, which may prevent the scarring that destroys kidney function.

Prevention

There is no known way to prevent PKD, but certain life-style modifications can help control symptoms.

People who have PKD should not drink heavily or smoke. They should not use aspirin, non-steroidal anti-inflammatory drugs, or other prescription or over-the-counter medications that can impair kidney function.

People who have PKD should eat a balanced diet, exercise regularly, and maintain a weight appropriate for their height, age, and body type. Regular medical monitoring is recommended.

Key Terms

Biopsy

The surgical removal and microscopic examination of living tissue for diagnostic purposes.

Cancer

A fatal disease, if left untreated, of neoplasms (tumors or growths). Cancer cells spread in the body and invade other tissue.

Computed tomography (CT) scan

A medical procedure where a series of X-rays are taken and put together by a computer in order to form detailed pictures of areas inside the body.

Cyst

A fluid filled sac lined by epithelium (the covering of the internal and external organs of the body).

Diuretics

Medications that increases the excretion of urine.

Kidney

Either of two organs in the lumbar region that filter the blood, excreting the end products of the body's metabolism in the form of urine and regulating the concentrations of hydrogen, sodium, potassium, phosphate and other ions in the body.

Magnetic resonance imaging (MRI)

A medical procedure used for diagnostic purposes where pictures of areas inside the body can be created using a magnet linked to a computer.

Ultrasonogram

A procedure where high-frequency sound waves that cannot be heard by human ears are bounced off internal organs and tissues. These sound waves produce a pattern of echoes which are then used by the computer to create sonograms or pictures of areas inside the body.

Uremic poisoning

Accumulation of waste products in the body.

Further Reading

For Your Information

Books

• Shaw, Michael, ed. Everything You Need to Know About Diseases. Springhouse, PA: Springhouse Corporation, 1996.

  Organizations

• Polycystic Kidney Research Foundation. 4901 Main Street, Kansas City, MO 64112-2634. (800) PKD-CURE. http://www.kumc.edu/pkrf/.

  Other

• PKD Patient Information. http://www.kumc.edu/pkrf/pkd/arpkd.html (25 May 1998).
• Polycystic Kidney Disease. http://www.healthanswers.com/database/ami/converted/000502.html (25 May 1998).
• Treating Polycystic Kidney Disease. What Does the Future Hold? http://www.coolware.com/health/medical_reporter/kidney1.html (26 May 1998).

Gale Encyclopedia of Medicine. Gale Research, 1999.