POLYCYSTIC KIDNEY DISEASE – Pathophysiology, Clinical Manifestations, Diagnostic Evaluations and Management
Polycystic kidney disease (PKD) is an inherited disease that affects the kidneys. Sacs of fluid (called cysts) grow in the kidneys. If too many cysts grow or if they get too big, the kidneys become damaged. The cysts may also cause pain or may get infected.
In PKD, cysts or fluid-filled pouches are found primarily in the kidney but they can also affect other organs, including the liver, pancreas, spleen and ovary. Out-pouching may occur in the walls of the large intestine and in the walls of blood vessels in the brain, where they may cause aneurysms. They may also be found in the abdominal wall, causing hernias. In addition, valves of the heart may be involved, becoming floppy and resulting in a heart murmur in some patients.
TYPES POLYCYSTIC KIDNEY DISEASE
There are two major forms of polycystic kidney disease: autosomal dominant polycystic kidney disease and autosomal recessive polycytic kidney disease.
- Autosomal dominant polycystic kidney disease: the adult type of PKD (also called autosomal dominant PKD or ADPKD) is passed from parent to child by an autosomal dominant type of inheritance. This means that only one copy of the abnormal gene is needed to cause the disease. Therefore, if one parent has the disease, each child has a 50-50 chance of developing the disease. ADPKD is a common disorder, occurring in approximately 1 in every 400 to 1000 people. Only about one half of people with ADPKD will be diagnosed during the person’s lifetime because the disease is often without symptoms.
- Autosomal recessive polycystic kidney disease: the less common form of PKD (also called autosomal recessive PKD or ARPKD) is passed by an autosomal recessive pattern of inheritance. This means that both parents must carry the abnormal gene and both must pass the gene to the child in order for the child to develop the disease. In this situation, every child has a 25 percent chance of developing the disease in a family that is at risk. The estimated incidence is 1 in 10,000 to 20,000 people. Autosomal recessive means that the mutated gene must be present in both parents; a person who has only one abnormal gene is a carrier.
PATHOPHYSIOLOGY
Persons with PKD have multiple clusters of cysts form on the kidneys. The exact action that triggers cyst formation is unknown. In early stages of the disease, the cysts cause the kidney to swell, disrupting kidney function and leading to chronic high blood pressure and kidney infections. The cysts may cause the kidneys to increase production of erythropoietin, a hormone that stimulates production of red blood cells. This leads to too many red blood cells, rather than the anemia seen in chronic kidney disease. Bleeding in a cyst can cause flank pain. Kidney stones are more common in people with PKD.
PKD is associated with the following conditions:
- Brain aneurysms
- Cysts in the liver, pancreas and testes
- Diverticula of the colon
CLINICAL MANIFESTATIONS
- Abnormal pain or tenderness
- An increase in the size of the abdomen
- Blood in the urine
- Excessive urination at night
- Flank pain on one or both sides
- Frequent kidney infections
Additional symptoms that may be associated with the disease include the following:
- Drowsiness
- High blood pressure
- Joint pain
- Nail abnormalities
- Painful menstruation
DIAGNOSTIC EVALUATIONS
Examination may show high blood pressure, kidney or abdominal masses, abdominal tenderness over the liver, and enlarged liver. There may be heart murmurs or other signs of aortic insufficiency or mitral insufficiency. A urinalysis may show urine protein or blood in the urine. A CBC may show decreased or increased RBCs and hematocrit. Cerebral angiography may show associated aneurysms.
Polycystic kidney disease and associated cysts on the liver or other organs may be detected with the following tests: abdominal ultrasound, abdominal CT scan, abdominal MRI scan and IVP. In a family with several members with PKD, genetic tests can be done to determine whether a person at risk carries the PKD gene.
MANAGEMENT
No treatment is available for the cysts caused by PKD. If the cysts are causing symptoms, these symptoms can be treated so patient will be more comfortable. The goal of treatment is to control symptoms and prevent complications. Treating high blood pressure can have a dual benefit in people with polycystic kidney disease because it can slow the decline in kidney function and minimize the risk that a cerebral aneurysm will rupture. People with high blood pressure are much more likely to develop kidney failure. Angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) can effectively lower blood pressure in most people with ADPKD.
Low protein diets have not proved helpful to PKD patients with advanced kidney disease. Reducing salt in the diet helps control blood pressure in PKD patients who have high blood pressure. A diet low in fat and moderate in calories is recommended to maintain a healthy weight.
Any urinary tract infection should be treated promptly with appropriate antibiotics. Cysts that are painful, infected, bleeding or causing an obstruction may need to be drained. Surgical removal of one or both kidneys may be required. Treatment of end-stage kidney disease may include kidney dialysis or kidney transplantation. In the meantime, many supportive treatments can be done to help prevent or slow down loss of kidney function in PKD. These include: careful control of blood pressure, prompt treatment of any bladder or kidney infections, lots of fluid and bed rest when blood in the urine is first noted a healthy lifestyle with regard to smoking, exercise, weight control and salt intake.
POLYCYSTIC KIDNEY DISEASE – Pathophysiology, Clinical Manifestations, Diagnostic Evaluations and Management