PKD, or Polycystic Kidney Disease, is a relatively common cause of kidney disease in cats, and usually has a genetic cause. Unfortunately, it is currently incurable; however, there are medical treatments available that mean affected cats can, with suitable care, live a largely normal and comfortable life.
What is it though?
Cats with PKD gradually develop fluid-filled cysts in their kidneys. Over time, more and more of these cysts form, and they get bigger and bigger. In the process, they compress the kidney tissue between them. Eventually, so much of the healthy kidney tissue has been crushed by the cysts that kidney failure develops.
What causes it?
Although there are a number of possible causes (including some drugs, such as long-term steroid use), in the vast majority of cases there is a genetic mutation in the cat’s DNA that triggers the production of cysts. The most common form is called AD-PKD, and is known as an “autosomal dominant” mutation. This means that a cat only needs to inherit one copy of the mutant gene to develop the disease.
This gene is very common in Persian cats – where it is estimated that up to 40% are affected. However, other related cat breeds may be affected too, including Exotic Shorthairs, Himalayans, and Scottish Fold Cats. In other breeds, PKD occasionally crops up too, as a result of other, rare, mutations.
What does it lead to?
While the cysts may sometimes be uncomfortable or even painful, ultimately, the concern is that they will inevitably cause Chronic Kidney Disease (CKD). This occurs once 75% of the functional kidney tissue has been damaged, as the remaining 25% is insufficient to filter the blood effectively. The kidney is a complex and intricate organ, responsible for removing wastes from the blood, controlling water and salt balance, regulating blood pressure, and triggering the production of red blood cells. All of these functions can be impaired in kidney failure.
The symptoms we typically see include:
- Increased urination and thirst
- Loss of appetite
- Weight loss (which may be dramatic)
- A metallic smell on the breath (due to a build-up of wastes)
- Constipation and/or diarrhoea
- Muscle weakness (caused by low blood potassium levels)
- Pale gums and breathlessness (due to anaemia)
- Sudden onset blindness (as a result of high blood pressure causing a retinal bleed)
- Collapse and, ultimately, death
While the gene is present from conception, in most cases the cysts develop only slowly. While cysts have been detected as early as 7 weeks, symptoms will not usually appear until the cat is several years old.
How is it diagnosed?
Kidney failure is usually diagnosed from blood and urine tests. Blood tests will show increased urea, creatinine and phosphorus (waste products filtered by the kidneys), and lower potassium. Urine tests tend to show dilute urine and high protein levels. However, as mentioned above, kidney failure usually takes years to develop, and there are many other possible causes, so these tests are not useful for determining whether the cat has PKD.
In older animals (over 6 months), ultrasound scanning of the kidneys is usually reliable – affected cats almost always have one or more cysts by this age. In younger kittens, genetic tests are preferred – in a high-risk breed, the exact mutation that that breed suffers from can be screened for. If the mutation is present, the cat will develop PKD.
Can it be treated?
Occasionally, the fluid-filled cysts become infected. If this is the case, cats tend to be severely painful and very sick. The treatment is antibiotics and sometimes surgical drainage of the cyst, or even removal of the kidney. Fortunately, this is pretty uncommon.
Far more common is early-onset chronic kidney failure. Although the PKD cannot be treated, this kidney failure can usually be managed. The mainstays of treatment are:
- Special diets (usually with reduced protein and phosphate, and sometimes increased or supplemental potassium too).
- Kidney support medicines (such as ACE-inhibitors like benazepril).
- Blood pressure monitoring and management (e.g. amlodipine tablets).
The short-term prognosis for a cat with PKD is actually quite good; and even once kidney failure develops, affected cats can usually be kept comfortable for a prolonged period with early diagnosis and suitable management.
If you are concerned your cat may have PKD, or any other kidney disease, make an appointment to see one of our vets to be checked out!