POLYCYSTIC KIDNEY DISEASE (PKD)
What is Polycystic Kidney Disease? Back to Page Index
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.
International Cat Care has some information about PKD.
Symptoms Back to Page Index
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.
Diagnosis Back to Page Index
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.
DDC Veterinary in Ohio offers a similar test for US$48.
In the EU the test is offered by The University of Bristol Langford Veterinary Services for £31.50 (you can print a freepost label to use within the UK, or by the Animal Health Trust at a cost of £54.
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 & Surgery 11 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.
Treatments Back to Page Index
PKD is incurable and sadly, there are very few treatments available. Try to ensure that your cat leads a stress free life, free of infection and toxicity. A soy protein diet may possibly help.
Potassium citrate/citric acid intake improves renal function in rats with polycystic kidney disease (1998) Tanner GA American Society of Nephrology 9 pp1242-48 indicated that potassium citrate may help PKD rats; it is not known if this also applies to cats, but potassium citrate is an ingredient in Royal Canin's Persian cat food.
Selective ablation of symptomatic dominant renal cysts using 99% ethanol in adult polycystic kidney disease (2006) Singh I & Mehrotra G Urology 68(3) pp482-7 was a study in India that found that injecting alcohol into cysts helped humans patients whose primary symptom was pain from dominant cysts. I am not aware of any evidence that this would help cats, though in 2013 I did hear from one person whose vet was considering this treatment for her cat.
If the PKD develops into CKD, then the usual CKD treatments can be used as appropriate, as described elsewhere in this site.
Research Back to Page Index
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.
Sirolimus therapy to halt the progression of ADPKD (2010) Perico N, Antiga L, Caroli A, Ruggenenti P, Fasolini G, Cafaro M, Ondei P, Rubis N, Diadei O, Gherardi G, Prandini S, Panozo A, Bravo RF, Carminati S, De Leon FR, Gaspari F, Cortinovis M, Motterlini N, Ene-Iordache B, Remuzzi A, Remuzzi G Journal of the American Society of Nephrology 21(6) pp1031-40 found that sirolimus "halted cyst growth" in human patients with PKD. Sirolimus (rapamycin) is an immunosuppressant drug used to prevent rejection in organ transplants, particularly kidney transplants.
Autosomal dominant polycystic kidney disease: pathophysiology and treatment (2007) Rapoport J Quarterly Journal of Medicine 100 pp1-9 reports on a number of possible treatments for humans with PKD.
Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease (2004) Torres VE, Wang X, Qian Q, Somlo S, Harris PC, Gattone VH 2nd Natural Medicine 10(4) pp363-4 reports on the use of OPC-31260 in mice.
Effectiveness of vasopressin V2 receptor antagonists OPC-31260 and OPC-41061 on polycystic kidney disease development in the PCK rat (2005) Wang X, Gattone V 2nd, Harris PC, Torres VE Journal of the American Society of Nephrology 16(4) pp846-51 reports on research on rats into OPC-31260 and another drug called OPC-41061.
This page last updated: 21 September 2013
Links on this page last checked: 03 April 2012