Non-Inherited Polycystic Kidney Disease

Cystic kidney disease is a condition in which the kidney develops several fluid-filled sacs or cysts. It may develop in both children and adults. It is usually seen in:

• People with chronic kidney disease (CKD)
• People with end-stage renal disease (ESRD), especially on those who are on dialysis. The risk of developing these cysts increases as the period on dialysis lengthens.
• The formation of multiple cysts is also seen in conditions that cause hypokalemia, certain metabolic conditions, and toxic injury to the kidney

Acquired cystic kidney disease does not usually present with any symptoms unless complications set in.

Inherited vs non-inherited cystic kidney disease

Unlike the large cyst-filled kidneys found in people with inherited polycystic kidney disease (PKD), the kidneys in acquired cystic kidney disease are normal in size or smaller, and there is no genetic cause for the cysts. Rather, they are due to the damage that has occurred to the renal tissue. Patients with genetic PKD have a family history of similar disease, unlike those with the acquired type.

There is also no cyst formation in other parts of the body, whereas liver and pancreatic cysts are common in the inherited condition. Cysts herald the slow progression to CKD in the genetically caused PKD. On the other hand, cysts occur several years after the onset of CKD in the acquired type.  

Pathogenesis of acquired cystic disease of the kidneys

The incidence of cystic kidneys varies from between 7-22% in people who suffer from chronic kidney disease but are not on dialysis, to almost 90% in those who have been on dialysis for 8 years or more. The cause of cyst formation is as yet not understood, but has to do with the kidney disease itself.

CKD results in the accumulation of several metabolic waste products in the blood. Many of these, but not all, are removed from the blood by dialysis. It is thought that one of the waste products which is not filtered by dialysis accumulates in the body, and is responsible for cystic formation in the renal tissue. This is supported by the finding that cystic changes often regress in the damaged kidneys after a successful kidney transplant (the diseased kidneys are not routinely removed during a transplant).

Complications

Complications related to cystic kidney disease include:

• Infection of a cyst
• Bleeding into a cyst with resulting pain and hematuria
• 10-20% of developing kidney tumors
• A slightly higher chance of cancerous kidney tumors

Diagnosis and treatment

Diagnosis of cystic kidney disease is on the basis of symptoms such as back pain, fever and bloody urine in a patient who is on long-term dialysis. It may be confirmed using imaging tests such as ultrasound, CT scanning or MRI scanning to visualize the kidneys. Treatment largely deals with symptoms, such as draining large cysts which are causing pain, antibiotics to control infection, and tumor removal. Regular screening at intervals of three years is sometimes advised for all patients with CKD, especially if they develop tumors.

References

• http://www.niddk.nih.gov/health-information/health-topics/kidney-disease/acquired-cystic-kidney-disease/Pages/facts.aspx
• Martinez JR, Grantham JJ. Polycystic kidney disease: etiology, pathogenesis, and treatment. Dis Mon 1995; 41 (11): 693–765
• Chapman AB, Rahbari-Ouskoui FF, Bennett WM. Acquired cystic disease of the kidneys in adults. UpToDate website. http://www.uptodate.com/contents/acquired-cystic-disease-of-the-kidney-in-adults?source=search_result&search=acquired+cystic+disease+of+the+kidney+inadults&selectedTitle=1~150