What is polycystic kidney disease?
Polycystic kidney disease (PKD) is a hereditary kidney disease that is common in cats, but uncommon in dogs.
Affected dogs begin to develop multiple small cysts within both kidneys early in life. As the dog ages, these cysts gradually increase in size and number. As they multiply, the cysts replace normal, functioning kidney tissue. This leads to a decrease in the amount of kidney tissue that is available to remove waste products from the bloodstream. Over time, affected dogs develop signs of chronic kidney disease.
What causes polycystic kidney disease?
PKD is an inherited condition. Dogs who receive a defective copy of the gene from either one of their parents may show signs of polycystic kidney disease (autosomal dominant inheritance).
PKD is most diagnosed in bull terriers. Other predisposed breeds include Cairn terriers and West Highland white terriers.
What are the signs of polycystic kidney disease?
In young dogs, PKD is typically asymptomatic, although not always. As dogs age, functional kidney is gradually displaced by cysts and kidney function decreases. The clinical signs of polycystic kidney disease are often first observed in mature, middle-aged dogs.
Signs of kidney disease are variable. You may notice that your dog is drinking or urinating more than usual. The kidneys lose the ability to concentrate the urine, so the dog must drink more and more to avoid dehydration. Your dog may experience a decreased appetite or weight loss as an early sign of kidney disease. In later stages, nausea, vomiting, or diarrhea may occur as a result of waste product buildup in the blood stream.
How will my veterinarian diagnose polycystic kidney disease?
Your veterinarian will begin by performing a physical exam. In some cases, your veterinarian may be able to detect enlarged or irregular kidneys on abdominal palpation. More frequently, however, the only signs on physical exam are nonspecific, such as weight loss and dehydration.
After a thorough physical exam, your veterinarian will likely perform blood tests. These tests typically include a complete blood cell count (CBC) and serum biochemistry. Your dog’s CBC may show evidence of anemia, which can occur when diseased kidneys fail to adequately stimulate red blood cell production. Your dog’s serum biochemistry will likely show elevations in three indicators of kidney function: BUN (blood urea nitrogen), creatinine, and SDMA (symmetric dimethylarginine). There may also be abnormalities in electrolytes and elevations in calcium and phosphorus.
Your veterinarian will also perform a urinalysis. This test involves analyzing the chemical composition of your dog’s urine, as well as examining the urine under a microscope. A urinalysis can indicate how well your dog’s kidneys are functioning and if your dog is losing protein through the urine, which is common in dogs with polycystic kidney disease. It will also look for the presence of a urinary tract infection and crystals.
Imaging is often required to detect polycystic kidney disease. X-rays can sometimes show visibly enlarged and irregular kidneys but may not be sensitive enough to diagnose early polycystic kidney disease. Ultrasound is typically recommended as a more sensitive test. It provides a much more detailed view of the kidneys, allowing small, individual cysts to be detected, even in young puppies.
Additional diagnostic tests may include genetic testing, histopathology (examining kidney tissue under a microscope), and computed tomography (CT scan).
How is polycystic kidney disease treated?
There is no treatment for PKD, specifically. Dogs with PKD are treated the same as dogs with any other form of chronic kidney disease. Treatments may include a prescription diet, fluid supplementation, and medication to manage the effects of chronic kidney disease.
Dogs vary significantly in how rapidly cysts develop and renal failure progresses. Many dogs with PKD can survive to 8-10 years of age, as long as appropriate treatment and monitoring are provided.
How is polycystic kidney disease prevented?
The only way to prevent polycystic kidney disease is to avoid breeding affected dogs. This can be challenging, because most dogs do not show any evidence of the disease until they are past prime breeding age.
Given the increased risk of this condition in bull terriers, genetic testing is recommended to screen bull terriers prior to breeding. This test is relatively inexpensive and is easy to perform. Talk to your veterinarian for more information.
