Polycystic Kidney Disease
Polycystic kidney disease (PKD) is a genetic condition in which multiple fluid-filled sacs or cysts develop throughout the kidneys. These cysts vary in size and number, and may affect the ability of the kidneys to function. PKD cysts may eventually cause kidney damage if they become very large and numerous.
PKD is the fourth leading cause of kidney failure in North America. It is estimated that approximately 5% of patients requiring dialysis or a kidney transplant have PKD.
Depending on the type of PKD, symptoms usually begin either in early adulthood, between the ages of 30 and 40 years, or in infancy or early childhood. PKD can be detected by ultrasound. Both men and women of all races seem to be affected equally.
PKD is an inherited disease. This means that it is passed on from parents to children through genes. There are two types of PKD.
90% of people with PKD have autosomal dominant polycystic kidney disease (ADPKD), or adult PKD. The remaining 10% have autosomal recessive polycystic kidney disease (ARPKD), which affects infants and children.
ADPKD, or adult PKD, occurs when one parent has passed the gene on to a child. Because the gene is dominant, there is a 50% chance that a child will get PKD if one parent has the disease. In some cases, however, this form of PKD can occur spontaneously as a result of a new genetic mutation and is not passed on from parents.
ARPKD is the rarer form of PKD. ARPKD happens when each parent is a "silent carrier." This means that the parents carry the gene but are not affected by PKD. There is a 25% chance that a child born to parents that are both carriers will get the disease. If only one parent carries the gene, children will not be affected.
Symptoms and Complications
The kidneys, which are each about the size of a fist, play three major roles:
- removing waste products from the body, keeping toxins from building up in the bloodstream
- producing hormones that control other body functions, such as regulating blood pressure and producing red blood cells
- regulating the levels of minerals or electrolytes (sodium, calcium, and potassium, for example) and the levels of fluid in the body
In early PKD, there are usually no symptoms. About half of people with PKD never get symptoms and are never diagnosed. People who develop symptoms will generally do so between the ages of 30 and 40. The symptoms are directly related to infections, swelling of the cysts, or the body's inability to remove harmful toxins that are circulating in the bloodstream.
The most common symptoms of PKD include back or side pain (between the ribs and hips), tenderness around the abdomen, or a feeling of fullness.
Someone with PKD might experience:
- bloody urine
- kidney infections
- cysts elsewhere in the body, such as the liver and pancreas
- abnormal heart valves
- kidney stones
- hypertension (high blood pressure)
- abdominal pain (from the enlarged kidneys pressing on the abdomen)
- puffy eyes, hands, and feet (called edema)
- increased urination, especially at night
- pain or difficulty passing urine
- varicose veins
Urinary tract infections (UTI) and kidney stones are common among people with PKD. About 20% to 30% of people with PKD develop kidney stones. High blood pressure occurs in about 60% to 70% of people with PKD and for many is the first sign of the disease.
People with PKD have a 5% to 10% risk of developing an intracranial (brain) aneurysm (bulging in the wall of a blood vessel). Some aneurysms can leak or rupture, causing symptoms such as sudden severe headache, nausea and vomiting, and pain when moving the neck. There is a higher risk of rupture in people with a family history of aneurysm or uncontrolled high blood pressure. These symptoms require immediate medical attention.
Cysts may also appear in other parts of the body such as the liver, pancreas, colon, testes, and brain. About one-quarter of people with PKD also develop weakened heart valves, which can sometimes lead to the need for valve replacement surgery.
By the age of 75, 50% to 75% of people with PKD will need either dialysis or a kidney transplant. This is more common in men and those with high blood pressure or an earlier age of diagnosis.
Making the Diagnosis
Family history is important in reaching a diagnosis. The less common ARPKD can only be diagnosed through testing.
The most reliable way to diagnose polycystic kidney disease (PKD) is by an ultrasound of the kidneys – the images allow the doctors to see the cysts, and more specifically, their size and how numerous they are. Occasionally, PKD is discovered by accident during an ultrasound or through blood or urine tests being done for other reasons. Blood tests can show a buildup of toxins such as urea, while urine tests can show that the kidneys aren't filtering properly, allowing protein or red blood cells to pass through.
When PKD cysts are quite numerous and large, doctors are sometimes able to palpate (feel) them.
CT or CAT (computed tomography) scans and MRIs (magnetic resonance imaging) also allow doctors to see the cysts, but the diagnosis can usually be made with an ultrasound.
Treatment and Prevention
Although PKD does not have a cure, specific therapy, or treatment, most people with PKD can lead a normal life. The goal of treatment is to ease the symptoms and prevent infections and other problems that can make the condition worse. Treatment is needed to keep complications (such as kidney failure) from occurring or to delay their development.
Pain: In order to relieve pain from the cysts, the larger cysts can sometimes be drained of the fluid, relieving pressure on the area around them. To do this, a small catheter (a very small, flexible tube) is inserted into the cyst to remove the fluid. In severe cases, surgery might be needed to remove the cysts, but this is usually only a temporary solution. Since many pain medications are removed from the body by the kidneys, people with PKD should check with their doctor or pharmacist before starting any medications for pain.
Hypertension: Controlling high blood pressure is important to prevent further kidney damage. Treatment of high blood pressure might involve changes in lifestyle (exercise, diet, stress reduction) and medications.
Urinary tract infections (UTIs): UTIs should be treated as soon as possible, usually with antibiotics, since infection can cause further damage to the kidneys.
Kidney failure: If PKD results in kidney failure (end-stage renal failure) and all other treatments have not stopped the progression of kidney damage, dialysis, or a kidney transplant may be considered.
Dialysis is a process that removes excess fluids and wastes from the bloodstream using a membrane – instead of a kidney – as a filter. Kidney transplants are relatively common now and have a good success rate. Someone who has had a successful transplant can go on to live a normal, healthy life for many years.
Dietary changes: People with PKD should limit their dietary sodium intake to 2 grams per day or less.