Polycystic Kidney Disease Definition

Polycystic kidney disease (PKD) is a condition marked by the formation of cysts in the kidney. In some cases, the sac-like cysts can also be seen in the pancreas, liver, and spleen. It is one of the most common genetic disorders, running in the families and a common cause of kidney failure in adults. This progressive disease shows symptoms usually in adulthood but children and newborns may also have cysts. However, it is important to note that polycystic kidney disease (PKD) is a multisystem illness meaning that it can affect many other organs in the body and not just the kidneys.

Polycystic Kidney Disease Types

Polycystic kidney disease can be of two types :

Autosomal dominant PKD (ADPKD)

Autosomal dominant inheritance means that the abnormal gene from even one parent is sufficient to inherit the disease. ADPKD is the most common inherited form, present in 90% cases of PKD. It can be asymptomatic for long periods of time before symptoms develop, usually between the ages of 30 to 40 years.

Autosomal recessive PKD (ARPDK)

Autosomal recessive inheritance means that two copies of the abnormal gene must be present to inherit the disease. ARPKD is the rare form. Symptoms begin in the earliest months of life, even in the womb.

Polycystic Kidney Disease Incidence

Polycystic kidney disease affects about 1 in 1,000 people in the United States. It contributes to about 10% cases of end stage renal (kidney) disease (ESRD). Kidney failure from polycystic kidney disease is mostly reported in adults.

Polycystic Kidney Disease Pathophysiology

Cysts in the kidney

Cysts are fluid-filled cavities in tissue. It should not be mistaken for an abscess which is pus filled sac associated with an infection. The number of cysts increases progressively in both kidneys in polycystic kidney disease. In some cases, cysts in the liver, ballooning of blood vessels supplying to the brain (cerebral aneurysms), and heart valve abnormalities are also seen together with the kidney cysts.

Kidney cells (nephrons) are made up of a capsule like structure called the renal corpuscle and surrounding tubules. A mutation in PKD gene leads to repeated multiplication of nephrons. The rapidly multiplying cells form a sac-like cyst that fills with fluid. A further expansion may cause separation of the emerging cysts from the initial site of their formation. In the process healthy kidney tissue is compromised.

Many changes take place in the kidney tissue during this process. The basement membranes of the tubules thicken and are infiltrated by immune cells called macrophages. New blood vessels develop and excess fibrous tissue (scarring) starts forming. Various growth factors that are already present in the tissues promote further multiplication of cells. As a result, cysts become self-sufficient structures and lead to kidney enlargement.

Effects on the kidney

The functional changes arising from these events can be summarized as:

  • Decreased ability of concentrating the urine
  • Bleeding resulting from damage to the new blood vessels
  • Expansion of cysts due to accumulated blood, resulting in severe pain
  • Blood in urine upon continued bleeding
  • Pooling of blood in the abdominal cavity

Polycystic Kidney Disease Causes

PKD Genes

Cysts are usually caused by abnormalities in the genes PKD1 and PKD2. PKD1 gene codes for the protein polycystin 1 and PKD2 gene codes for polycystin 2. Polycystin 1 protein regulates the functioning of kidney tubules whereas polycystin 2 controls fluid secretion. Abnormalities in these proteins alter the function of the flow sensors of the kidney called renal cilia. This results in the filling of the cysts with secreted fluid and it enlarges. This affects filtration process of the kidney and leads to kidney dysfunctions.

Polycystic Kidney Disease Symptoms

Symptoms of polycystic kidney disease may include:

  • High blood pressure
  • Blood in the urine
  • Frequent urination
  • Bloating of the abdomen
  • Headache
  • Kidney stones
  • Urinary tract infections or kidney infections
  • Kidney failure

Pain in the back and flanks is reported by almost all PKD patients. The pain can be caused by either enlargement of cysts, bleeding, urinary tract infections, kidney stones, inflammation of colon in patients on dialysis, or cancer of kidney tubules.

Polycystic Kidney Disease Complications

Polycystic kidney disease can lead to following complications:

  • High blood pressure is commonly seen. If left untreated, it can further damage the kidneys and increase the risk of stroke and heart disease.
  • Progressive loss of kidney function is the most serious complications of PKD, requiring kidney dialysis or kidney transplant.
  • In some pregnant women, polycystic kidney disease can lead to a life-threatening condition called preeclampsia.
  • PKD increases the risks of developing cysts in the liver, aneurysms in the brain, and abnormalities in the heart valve.
  • Colon inflammation may develop in patients on dialysis.
  • Chronic pain in the abdomen, side or back.

Polycystic Kidney Disease Diagnosis

A number of different blood and urine tests will verify the dysfunction of the kidney. However, imaging studies are necessary to confirm the diagnosis of polycystic kidney disease. The main imaging studies for assessing the size of the kidney and the number of cysts within it includes :

  • Ultrasonography
  • Computed tomography (CT) scan
  • Magnetic resonance imaging (MRI)

Polycystic Kidney Disease Treatment

Various medical treatments are necessary for controlling the symptoms and minimizing the chance of any complications. Patients with end-stage renal disease may require dialysis or kidney transplantation.

Blood pressure

Medications called angiotensin-converting enzyme (ACE) inhibitors like enalapril, captopril, and lisinopril, or angiotensin II receptor blockers (ARBs) like telmisartan, irbesartan, losartan, and candesartan are frequently recommended to treat hypertension.

Infections

Antibiotics (ciprofloxacin, clindamycin, trimethoprim-sulfamethoxazole, and chloramphenicol) penetrate into the cyst and treat infections.

Bleeding

Bleeding is usually self limiting. Simple measures like drinking large amounts of water and rest is recommended. Pain associated with bleeding can be treated with analgesics.

Abdominal pain

Cyst decompression helps most of the patients. Drugs like nonsteroidal anti-inflammatory drugs (NSAIDs) are avoided because of their toxic side effects on the kidneys.

Polycystic Kidney Disease Surgery

Surgical  measures are only considered when the cysts are very large, symptoms severe and medication alone is insufficient.

Cyst drainage

Larger cysts which are infected may need to be surgically drained. This procedure is recommended to antibiotic-resistant patients.

Nephrectomy

Surgical removal of the kidney (nephrectomy) is performed in severe cases of massive kidney enlargement. The patients who do not respond to traditional treatment and those who have inaccessible cysts qualify for this surgery.

References :

http://emedicine.medscape.com/article/244907-overview

http://www.mayoclinic.com/health/polycystic-kidney-disease/DS00245

http://www.merckmanuals.com/professional/genitourinary_disorders/cystic_kidney_disease/autosomal_dominant_polycystic_kidney_disease_adpkd.html

 


Article reviewed by Dr. Greg. Last updated on July 22, 2012