Polycystic Kidney Disease in Dogs
Polycystic kidney disease is a disorder in which large portions of renal parenchyma, the functional tissue of the kidneys which are normally differentiated, are displaced by multiple cysts.
A cyst is a closed sac that may be filled with air, fluid, or semi-solid material. Renal cysts develop in pre-existing nephrons -- the functional filtering cells of the kidney tissue -- and in the collecting ducts. Invariably, the disease both of the dog's kidneys.
Although polycystic kidney disease is usually not immediately life-threatening, it should be treated as early as possible to prevent cyst progression and development of secondary bacterial infection, either of which may lead to sepsis, the presence of pus-forming toxic organisms in the blood.
Both dogs and cats may develop polycystic kidney disease, with some breeds more susceptible than others. For instance, the Cairn Terrier and Beagle are most frequently affected by this kidney disease than other breeds.
If you would like to learn how this disease affects cats, please visit this page in the PetMD health library.
Symptoms and Types
Polycystic kidney disease may be difficult to detect in the initial stages. The cysts often remain undetected until they become large and numerous enough to contribute to kidney failure or an enlarged abdomen. Most patients do not exhibit any symptoms during initial stages of cyst formation and growth.
Once the disease has progressed, bosselated (lumpy) kidneys may be detected. This is discovered during an abdominal palpatation, in which the abdominal muscles twitch uncontrollably.
Most renal cysts are not painful, so the dog may not exhibit any discomfort, but secondary infection associated with the cysts may result in later discomfort.
The exact stimuli for renal cysts is not precisely known. Genetic, environmental, and endogenous factors appear to influence the development of this disease.
Endogenous compounds that are believed to contribute to cyst development include the parathyroid hormone (a hormone secreted by the parathyroid hormones of the endocrine system) and vasopressin (a peptide hormone synthesized in the hypothalamus area of the brain).
One diagnostic procedure that may be used if polycystic kidney disease is suspected is an evaluation of the fluids through fine needle aspirates of the kidney (in which fluid is removed via needle), which may help to pinpoint the origination of the cysts.
Additional diagnostic procedures that may be required include abdominal ultrasounds, which may reveal the presence of cysts in some organs, a urine analysis, and an examination of cystic fluid. A bacterial culture of cyst fluids can be done to determine if secondary infection has developed and needs to be treated. Hypertension, or high blood pressure, may also be present.
If polycystic kidney disease is not the cause of the dog's symptoms, alternate diagnoses may include an unnatural cell growth, such as tumor in the kidney, kidney failure, and a variety of other cystic diseases of the kidneys.
Elimination of renal cysts is not possible at this time, thus treatment is often limited to minimizing the consequences of cyst formation, such as infection in the kidneys. Periodic removal of fluid from large renal cysts with a needle (a process known as aspiration) can be used to minimize pain and reduce cyst volume, and a number of medications may be prescribed to deal with symptoms and secondary complications, such as bacterial infection.
Living and Management
Dogs with polycystic kidney disease should be monitored every two to six months for associated diseases, such as kidney infection, kidney failure, and increased pain. If bacterial infection and associated sepsis (the presence of pus-forming and toxic organisms in the blood) does not occur, the short-term prognosis is favorable -- even without treatment.
The long-term prognosis for dogs with polycystic kidney diseases usually depends on the severity of the condition, and any subsequent progression to kidney failure.
Because the exact cause of polycystic kidney disease is unknown, there is no specific preventative measure that can be taken. Selective breeding, however, may reduce genetic diversity, thereby increasing the frequency of other unwanted inherited traits in affected breeds.