Polycystic
Kidney Disease, known as PKD, is an
autosomal dominant genetic disease of the kidneys which is passed on by one or both
parents - siblings may be unaffected. PKD
affects around 6% of all cats, but appears to be more common in Persian cats,
British Shorthairs and others with Persian
ancestry. One of our cats, Harpsie (in the washbasin), had PKD.
The distinguishing characteristic of PKD is that cysts are present,
usually on both kidneys, and as the cat gets older, these cysts often
increase in size and multiply. Eventually kidney function may be
diminished to the extent that CKD develops.
PKD cats tend to develop CKD around the age of 5 - 7 years (Harpsie was
diagnosed at the age of 7) but seriously affected cats with multiple cysts
can fall ill as young as two. Stress or infection can accelerate this
disease. However, CKD is not inevitable - it depends how badly the kidneys
are affected, and some PKD cats die from other causes before reaching CKD
status. Harpsie lived to 14, so he managed seven years after his PKD
diagnosis, and although his cysts were growing he did not have CKD when he
died (he died of cancer).
PKD
FAQs - this
site gives a good overview of PKD.
PKD
Links - this site has not been updated recently, but it does
have many links about PKD, including the main
scientific references, most of which are still active.
PKD is usually
asymptomatic, but a PKD cat may exhibit
polydipsia (increased thirst),
and in some cases the kidneys will feel enlarged (though there are other
possible causes for this, see
renomegaly). Many PKD cats show a slight heart murmur and slightly
swollen kidneys before CKD develops, and male PKD cats are often
susceptible to FLUTD (feline lower urinary tract
disorder), which Harpsie also had. Harpsie also had
frequent kidney infections: these are relatively common in PKD cats
because the bacteria can burrow deep into the cysts.
If the disease
progresses so far that CKD results, then the usual CKD symptoms will be
present, and the usual treatments can be used as appropriate. PKD itself
is generally considered not to be a painful disease. Unfortunately, this
may not apply to cats who progress to severe end stage PKD: these cats may
suffer pain from the cysts growing rapidly and occasionally rupturing.
Sadly, nothing can be done to prevent this, but you do need to watch for it
occurring in a PKD cat so you can discuss your options (such as
painkillers)
with your vet.
The University of California at Davis
has
identified the gene mutation that causes PKD, and is now offering genetic testing at a cost of US$40 per
cat. The test can be run as soon as a kitten is 8-10 weeks old and
is almost 100% accurate. You can obtain the sample yourself, it is
obtained by non-invasive means so your vet does not need to be involved.
Details of how to apply for the test can be found
here. You will be sent the results via
e-mail.
The only other way to diagnose PKD properly
is via an ultrasound of the kidneys. This has the advantage of allowing
you to see how severe the cysts are. An ultrasound, as explained by
Evaluation of the repeatability of ultrasound
scanning for detection of feline polycystic kidney disease
(2010) Wills SJ, Barr FJ, Bradley KJ, Helps CR, Cannon MJ & Gruffydd-Jones
TJ Journal of Feline Medicine & Surgery11 p993, is also the
only way to diagnose non-autosomal dominant forms of PKD.
Ultrasound is a
reasonably accurate method of diagnosis if it is undertaken by somebody skilled
in sonography, and ideally with experience of PKD kidneys. Repeated scans
may need to be taken if the cat is very young as the cysts may not be
visible at that time: it is often hard to detect PKD in cats less than
nine months old. Cysts are rare in cats but not all cysts are necessarily
PKD; research is still being done in this area. Some PKD cats may also
show cysts in their liver - Harpsie also had these.
If you have a
Persian cat suspected of having
hypertrophic
cardiomyopathy (HCM), a type of
heart problem, and are planning to have the heart
examined by ultrasound, I would recommend having the cat's kidneys
examined by ultrasound at the same time in order to rule out PKD. This was
how we discovered that Harpsie has PKD - the cardiologist checked his
kidneys when he checked his heart.
There is limited research into the treatment of PKD in cats, since the
current focus is on eradicating it from breeding lines, which in the
longer term is of course the best approach. The following links contain
information about research into certain drugs which appear to slow the
progression of the disease in humans or mice, but I am not aware that
anyone has used these treatments in cats.
Polycystic
Kidney Disease, known as PKD, is an
autosomal dominant genetic disease of the kidneys which is passed on by one or both
parents - siblings may be unaffected. PKD
affects around 6% of all cats, but appears to be more common in Persian cats,
British Shorthairs and others with Persian
ancestry. One of our cats, Harpsie (in the washbasin), had PKD.
