Section: PKD Information In-depth

Polycystic Kidney Disease (PKD) is a slowly progressive, irreversible, inherited kidney disorder in Persian and Persian-related cats. Although reported in the veterinary literature for approximately 30 years, the disease and its genetic mode of inheritance has only been clearly understood in the last 10 years.

The disorder is present at birth. Multiple small cysts slowly grow in size, causing the kidney to enlarge dramatically. The cysts replace the normal kidney tissue, while kidney function continuously declines. The cysts can vary in size, from less than one millimeter to greater than one centimeter. The older an affected cat gets, the larger and more numerous are the cysts. PKD often progresses to cause clinical signs of kidney failure late in the catís life, with the average age being around seven years, although the slowly progressive nature of the disorder results in some cats not developing clinical kidney disease and death.

Clinical signs of PKD are non-specific and are similar to those seen in cats with chronic renal failure of any cause. These include depression, decreased appetite or anorexia, excessive drinking, excessive urination, weight loss and sporadic vomiting.

There are two forms of PKD in humans: Autosomal dominant PKD (ADPKD) and autosomal recessive PKD (ARPKD). The autosomal recessive form of PKD is uniformly fatal in people at a relatively young age, however the autosomal dominant form (ADPKD) is slowly progressive and is similar to PKD in cats. Genetic studies in cats have shown that PKD in cats in autosomal dominant. This means that if an affected cat is bred to a normal cat, 50 percent of the offspring will be affected.

Section: Veterinary Care In-depth

Diagnosis In-depth

Physical examination findings and routine laboratory data are both insufficient for confirming or refuting a diagnosis of PKD early in the course of the disease, because the kidneys remain normal in size and maintain their normal contour. As the disease progresses, and the size and number of cysts increase, the kidneys enlarge; this may be detected on physical examination.

In severe, advanced cases, cysts may protrude beyond the normal kidney surface, causing an irregular contour which can be felt on physical examination. If chronic renal failure develops, blood tests will detect this, but blood tests alone cannot identify the cause of the kidney failure as being due to PKD.

    Radiographs with or without contrast. X-rays may or may not be helpful, depending on the age of the cat and the extent of the disease. As cats with PKD get older, the kidneys enlarge, and this can be detected on the x-rays. Early in the course of the disease, the contour of the kidneys is usually smooth. Later in the disease, the outer surface of the kidney becomes more irregular. Injection of an intravenous dye can highlight the urinary system on the x-rays. This test is not very helpful early in the disease; however, as the disease progresses, the dye may outline numerous cysts present throughout the entire kidney.

    Ultrasound. This is a sensitive, non-invasive technique for diagnosing cysts in the kidney. Small cysts are often detected as early as six to eight weeks of age, and occasionally as young as four weeks of age. After 10 months of age, the disease can be diagnosed with approximately 95 percent accuracy, using the proper equipment and experience.

Therapy In-depth

There is no specific therapy for PKD at the moment. Treatment for cats with PKD in which the disorder has progressed to chronic renal failure is similar to that for chronic renal failure of any cause:

    Restricted protein and phosphorus diet. These diets help reduce the levels of kidney toxins that contribute to the clinical signs of kidney failure, and may in fact slow the progression of renal failure.

    Subcutaneous fluids. Some cats benefit from having their owners administer fluids under the skin. This helps encourage urination, maintain hydration and keep the levels of toxins in the bloodstream lowered.

    Phosphorus binders. Cats with kidney failure have an impaired ability to excrete phosphorus. Elevated phosphorus levels contribute to the progression of kidney failure in cats. Phosphorus binders will bind up much of the phosphorus in the diet, making it unavailable to the cat and preventing elevated levels from developing.

    Calcitriol (vitamin D). Cats with kidney failure cannot synthesize vitamin D properly. This may have deleterious effects on several body systems. Calcitriol is a synthetic form of Vitamin D. Administration of calcitriol must be monitored closely by your veterinarian

    Erythropoietin. This hormone is made by the kidneys and it instructs the bone marrow to maintain the proper number of red blood cells in the circulation. As the kidneys fail, they produce less erythropoietin, and cats become anemic. Cats with severe anemia may benefit from having erythropoietin prescribed.

    Antacids. Elevated levels of kidney toxins can cause stomach ulcers, nausea and vomiting. Antacids may help reduce these signs.

Section: Follow-up

Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up can be critical, especially if your pet does not rapidly improve.

    Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your pet.

    Feed any prescription diets.

Owners of cats with PKD should be informed that the disorder is inherited and that if the cat is bred, 50 percent of the offspring will be affected. Breeders of Persian and Persian-related breeds should have all of their cats and kittens evaluated using ultrasound for the presence of PKD. If a cat is found positive for cysts, its parents, siblings, and offspring should be evaluated. Those that are affected should be neutered or spayed so that they are effectively removed from the breeding population.

 

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