Polycystic Kidney Disease
Polycystic Kidney Disease
- polycystic disease of the kidneys
Polycystic kidney disease (PKD) is an inherited condition that results in ongoing kidney damage associated with cysts (abnormal fluid collections) occupying the kidneys. The abnormality also causes tissue laxity in other locations (blood vessels, liver, spleen).
What is going on in the body?
Polycystic kidney disease has two basic forms:
- "infantile" or so-called Autosomal Recessive Polycystic Kidney Disease based upon the way it is inherited (both parents pass on abnormal genetic material, but have the disease themselves) and
- "adult" or so-called Autosomal Dominant Polycystic Kidney Disease (one parent passes on the abnormal material and has the disease, but may not know it).
The autosomal recessive kind is usually fatal in infancy. The adult variety is responsible for kidney failure and is the reason for dialysis in 10% of the people on dialysis in the U.S.A.
Polycystic kidney disease results in malformed, enlarged kidneys, which are filled with small sacs, or cysts containing "urine-like" fluid, instead of normal kidney tissue. The cysts crowd out what is left of normal kidney tissue and cause kidney failure over time.
Abnormalities in other areas of the body may also occur. The blood vessel abnormalities may lead to aneurysms (outpouchings on blood vessels) which can rupture particularly in the brain. This may be rapidly fatal. Cysts in the liver are an issue in infants, but rarely cause problems in the adult variety. High blood pressure is common.
What are the causes and risks of the disease?
All forms of polycystic kidney disease are inherited or genetic.
In order for a child to inherit the infantile or childhood form of PKD, he or she must receive an abnormal gene from both parents. This form of inheritance is called autosomal recessive. Each parent has one abnormal gene and one normal gene, but neither parent has the disease itself. However, the each parent may pass the abnormal gene on to their children, causing the child to have 2 bad genes and thus the "infant" form of PKD.
The adult form of PKD only requires one abnormal gene, which is located on chromosome 16 and which can come from either parent. This type of inheritance is called autosomal dominant. In this situation, the parent with the abnormal gene has PKD.
However, it may be early enough in the course of the disease in the parent that the person transmitting the gene does not know that they have polycystic kidneys. Because he or she also has a normal gene, however, not all of the person's children are affected. It averages out to be 1 out of every two children who get the faulty gene.
What can be done to prevent the disease?
Polycystic kidney disease cannot be prevented in a person who has already been born. Genetic counseling may be helpful for couples with a family history of PKD. Early disease in a potential parent can be diagnosed by ultrasound, CT scan of the kidneys, or by genetic testing.
How is the disease diagnosed?
Diagnosis is usually based on the family history, physical exam, and imaging tests. Ultrasound and CT scans are commonly used imaging tests to show the kidney abnormalities. They will usually show abnormalities in the adult form when a person is in their twenties. In difficult cases without the usual findings, chromosome or genetic studies may help. A kidney biopsy should not be done with polycystic kidneys.
Long Term Effects
What are the long-term effects of the disease?
The infantile form of PKD almost always leads to death because of lung, liver, and breathing problems.
Adults usually progress to kidney failure and need dialysis and/or transplant. Some patients with the adult variety live lengthy lives and avoid kidney failure.
What are the risks to others?
Polycystic kidney disease is not contagious. Those who are affected may pass the condition on to their children (above).
What are the treatments for the disease?
Polycystic kidney disease cannot be cured or reversed, so treatment is directed at the problems that occur.
High blood pressure is treated with medications. Dialysis or kidney transplant may be needed for those who develop kidney failure.
Surgery to remove a kidney may be needed if long-term abdominal pain occurs or the kidney repeatedly becomes infected or bleeds. Other treatments may be needed for liver disease, but this is unusual.
Sometimes, surgery is needed to treat any abnormal brain arteries, or cerebral aneurysms. Kidney infections are common and are treated with antibiotics. Antibiotic choice is different because some antibiotics do not penetrate cysts.
What are the side effects of the treatments?
Side effects depend on the treatments used. For example, medication for high blood pressure may cause fatigue, allergic reactions, or erectile dysfunction. Antibiotics can cause stomach upset, allergic reactions, and other effects like colitis from C. difficile. .
Surgery carries a risk of bleeding, infection, and reactions to anesthesia. Dialysis has many side effects, including infection, salt imbalances, blood pressure swings, and weakness.
What happens after treatment for the disease?
Treatment usually lasts for life, because polycystic kidney disease cannot be cured and usually gets worse over time. If a transplant is received, the medications can predispose to infections and cancer.
How is the disease monitored?
Blood pressure control should be checked frequently. Blood tests are often used to monitor kidney function before kidney failure occurs. In addition to kidney function tests, potassium levels are monitored.
Blood tests also help to monitor someone on dialysis. Other monitoring depends on the complications that develop or if the patient gets a transplant. Any new or worsening symptoms should be reported to the healthcare provider.
Harrison's Principles of Internal Medicine, 1998, Fauci et al.