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
cat’s 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.