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Overview

Cystic kidney disease describes several conditions in which fluid-filled cysts form in the kidneys. Cysts generally develop in weak segments of the tubules that carry urine from the glomeruli. The cyst's growth displaces healthy kidney tissue. The kidneys expand to accommodate the cyst, which can weigh as much as 20 pounds.

Three factors determine cyst classification: its cause (acquired, inherited), its features (complicated, simple, multiple, single), and its location (outer [cortical] or inner [medullary] kidney tissue).

Types

Primary

• Polycystic kidney disease (PKD; common, with several cysts in the kidney)
  • Autosomal dominant
    • PKD type 1
    • PKD type 2
  • Autosomal recessive PKD

Secondary

• Aquired cystic kidney disease (ACKD)
• Medullary cystic disease (inner kidney)
  • Juvenile nephronophthisis (during adolescence)
  • Medullary sponge kidney (deterioration of kidney with cysts)
• Renal cell cancer associated cysts

Autosomal dominant medullary cystic kidney disease(MCK) causes cysts to form in the inner tissue of the kidney and can develop at a very early age. Recessive juvenile nephronophthisis usually occurs later than MCK, but is associated with similar symptoms, including chronic renal failure and growth problems. Small cysts in the collecting ducts of the inner kidney characterize medullary sponge kidney (MSK), which is associated with hematuria and kidney stones, but not chronic renal failure. Acquired cystic kidney disease (ACK) affects patients with chronic renal failure and causes hematuria, erythrocytosis (increase in red blood cells), and is associated with the development of cancer.

Incidence and Prevalence
Polycystic kidney disease (PKD) is the most frequently inherited disease; it affects approximately 600,000 people in the United States and over 12,000,000 worldwide. Most suffer from the autosomal dominant type. It is the fourth leading cause of kidney failure and causes 10% of all end-stage renal disease (ESRD; see CRF), usually between the ages of 40 and 60. It affects men, women, and races equally.

Risk Factors

If one parent has autosomal dominant PKD, there is a 50% chance the child will inherit it. If both parents have the gene for autosomal recessive PKD, there is a 25% chance their child will have the disease. If one parent carries the gene, the child will not develop it. Some people with PKD never develop symptoms and others develop cysts and hypertension in childhood.

Causes

PKD autosomal dominant types 1 and 2 are linked to a protein abnormality on chromosomes 16 and 4, respectively, and run in families. PKD autosomal recessive has been linked to chromosome 6. Causes of acquired cystic kidney disease (ACKD) are long-term disease (glomerulonephritis) and the scarring that often results from dialysis. ACKD is common among patients with chronic renal failure (CRF). Nearly all of those who use dialysis for more than 5 years develop ACKD.

Signs and Symptoms

Symptoms of PKD include those that affect the kidney as well as some that affect other organs, including the brain and liver. Though little is known about kidney-related cyst formation in other organs, it is probably related to abnormalities in the glomerular membrane.

Autosomal Dominant PKD

• Abdominal, back, or side pain caused by:
  • Enlarged kidney
  • Hemorrhage into cyst
  • Infected cyst
  • Kidney stone
  • Rupture of cyst
• Aneurysm (weakened blood vessel in the brain)
• Chronic renal failure (CRF) and end-stage renal disease (ESDR)
• Hematuria
• Hypertension
• Pancreatic and hepatic (in the liver) cysts

Autosomal Recessive PKD (infantile PKD)

• Enlarged cystic kidney at birth
• Hepatic fibrosis (abnormally small liver with scar tissue)
• Hypertension (high blood pressure)

Diagnosis

A nephrologist uses CT scan, x ray, and ultrasound to view kidney cysts. Autosomal dominant PKD is diagnosed when cysts are found in other organs as well as the kidney.

Scarring (sclerosis) of the liver distinguishes PKD recessive type and can be seen in a developing fetus.

Treatment

Treating PKD involves the following:

• Controlling pain, headaches
• Curing urinary tract infection (UTI)
• Controlling hypertension

Surgical reduction (removal) of cysts reduces pain in some people, especially if the cysts are large, but it does not alter the course of PKD and cannot stop cysts from developing. Surgery is performed with a laparacsope through a small incision in the abdomen. Headaches may be caused by vasculitis (i.e., swollen blood vessels in the head). Antibiotics are used to cure UTI before it spreads to the cysts and ACE inhibitors are used to lower blood pressure.

Renal replacement therapy, which involves kidney dialysis or transplantation, may be required in ESDR to restore kidney function. If the prospective kidney comes from someone in the family, genetic counseling and assessment is necessary. Cysts do not develop in healthy transplanted kidneys.

Prognosis
Many infants and children with recessive PKD die from hapatic fibrosis, which obstructs blood flow and causes bile buildup in the liver. Its symptoms are enlargement of the liver and the spread of a fibrous connective tissue over the liver. Those who survive into their 20s may develop splenic, pancreatic, and vascular problems. Children with recessive PKD often have smaller than average stature.

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