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Overview
Polycystic Kidney Disease is
a slowly progressive, irreversible, inherited kidney disease 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.
Ultimately, PKD can result
in renal (kidney) failure, with clinical signs similar to those of cats
with naturally occurring renal failure.
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 1 millimeter to greater than 1 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 7 years, although the slowly
progressive nature of the disorder results in some cats not developing
signs clinical renal disease as their bodies learn to adjust to the slowly
failing kidneys.
Clinical signs
Clinical signs of PKD are
non-specific and are similar to those seen in cats with chronic renal
failure of any cause. These
include lethargy, decreased appetite or anorexia, excessive
drinking, excessive urination, weight loss, and sporadic vomiting.
Diagnosis
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, and this may be detected on physical examination.
In severe, advanced cases, cysts may protrude beyond the normal
kidney surface, causing an irregular contour that can be felt on physical
examination. If chronic renal
failure develops, blood tests will detect this, but blood tests alone can
not identify the cause of the renal failure as being due to PKD.
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 is a sensitive,
non-invasive technique for diagnosing cysts in the kidney. Small cysts are
often detected as early as 6 to 8 weeks of age, and occasionally as young
as 4 weeks of age. After 10
months of age, the disease can be diagnosed with approximately 95%
accuracy, using the proper equipment and experience.
A genetic test is
available that is likely to become the test of choice for many breeders
because samples can be easily taken by veterinarians and shipped to
special laboratories that perform the test. Kittens do not have to be
10 months old before a reliable result can be obtained. Cats can be
tested at any age using a cheek swab. (Pre-weaning kittens, if being
tested, should have a blood sample drawn rather than a cheek swab, as
nursing kittens may have traces of the queen’s DNA in their mouth,
causing a false test result. It may be preferable to wait until the
kitten is weaned so that testing can be done using a cheek swab, which
is less stressful than taking a blood sample). Ultrasound screening will
always be available to clients and breeders who prefer this method of
diagnosis.
Treatment
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 renal
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 – the kidneys make a hormone that instructs
the bone marrow to maintain the proper number of red blood cells in the
circulation. The hormone is
called erythropoietin. 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.
- Careful monitoring of blood pressure – hypertension can increase
the rate of progression of kidney disease.
Anti-hypertensive medications can be given to bring the blood
pressure back to normal and reduce damage to the kidneys
Preventive Care
Prevention
requires responsible breeding to eliminate PKD from Persians and
Persian-related breeds. 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% of the
offspring will be affected. Cats
diagnosed with PKD should not be bred.
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.
Breeders of Persian and Persian-related breeds should have all of
their cats and kittens evaluated using
ultrasound or genetic testing for the
presence of PKD.
Updated 2/9/06 |
