14 | The VN's guide to caring for patients with polycystic kidney disease

PodcastRenal
Written By Laura Jones

Polycystic kidney disease is a genetic condition affecting patients from a young age, eventually causing advanced chronic kidney disease.

 

These patients benefit from early diagnosis and thorough supportive care, and we all know that veterinary nurses are vital in advocating for both of those things.

On top of that, client education is a huge part of this condition - and we all know nurses are great at that, too. But to advise our clients effectively, we need to have a good understanding of what PKD is, and how it affects our patients - and that’s exactly what we’re going to go through today.

What is polycystic kidney disease?

Polycystic kidney disease, or PKD, is an inherited condition seen in both cats and dogs, which causes multiple cysts to form in the kidneys. 

Inside the kidneys, a protein called polycystin-1 is required for the proliferation and differentiation of the epithelial cells within the renal tubules.

This glycoprotein is encoded by a gene called PKD1. Patients with PKD have an inherited faulty PKD1 gene, causing insufficient polycystin-1 production. Because the patient doesn’t have enough polycystin-1, they end up with remodelling of their renal tubules inside the nephrons, and cyst formation as a result.

All patients with PKD have cysts in their kidneys. These cysts start very small, so are virtually impossible to spot with imaging, and do not initially cause any renal dysfunction.

However, as the patient ages, their cysts grow - and ultimately, they reach a size where they do interfere with renal function, causing chronic kidney disease.

The rate of cyst growth varies from patient to patient. In most patients, the cysts grow slowly, with clinical signs of CKD becoming apparent in late young adulthood. However, some patients will develop advanced chronic kidney disease at a younger age - and there’s currently no way of predicting how quickly the disease will progress amongst individuals.

These cysts are not limited to the kidneys - other organs are also commonly affected, especially the liver and pancreas. So, hepatic function can also be affected as the patient ages. Cardiac disease has also been reported in patients with PKD. 

What causes PKD?

We know that PKD is a genetic condition. It’s defined as an autosomal dominant inherited condition, meaning that only one parent needs to have the defective gene to pass it on, and 50% of the litter will develop the condition.

It’s common in cats, and can also be seen in dogs - though less commonly. Around 6% of cats are affected, and Persians (as well as related breeds) are most commonly diagnosed with the condition, with around 37-50% of Persians and Persian-related breeds affected.

Let’s look at breed…

The highest-risk cat breeds include Himalayans, exotic shorthairs, British shorthairs, Scottish folds, and burmillas as well as Persians.

Breeds at moderate risk include Devon rexes, Radgolls, snowshoes, Birmans and Bombays, and lower-risk breeds include Bengals, burmese cats, Egyptian maus, Maine coons, Norwegian forests and orientals amongst others.

In dogs, bull terriers are the most commonly-diagnosed breed, though it is also seen in Cairn terriers, Beagles and west highland white terriers. 

What signs do we see in these patients?

Patients with polycystic kidney disease can be subclinical - and patients can have cysts documented on imaging but develop no clinical signs for a long time (or at all).

When clinical signs do occur, they are the same as patients with chronic kidney disease, because at this stage, the cysts have interfered with renal function for long enough to cause chronic kidney disease.

The cysts can also increase the risk of urinary tract infections and cause signs such as haematuria, and pollakiuria or stranguria.

And what about diagnosis?

PKD is diagnosed using a combination of bloodwork, urine analysis, imaging, and genetic testing.

The genetic testing is what will confirm our diagnosis of autosomal-dominant PKD - whereas biochemistry and urine analysis will document evidence of CKD, and imaging may show the presence of multiple renal cysts.

Let’s start by looking at bloodwork

Depending on the stage of CKD the patient is in at the time of presentation, increases in BUN and creatinine may be noted. In younger patients or those with normal creatinine levels, checking an SDMA is advisable, since this is a marker of early renal disease. 

Alongside azotaemia, we may also see other changes, such as hypokalaemia - because of increased renal potassium loss, and potentially a decreased dietary intake of potassium if the patient is inappetent or anorexic.

On haematology, we may see anaemia associated with a reduction in erythropoieitin production.

What do we see on urine analysis?

Urine analysis typically reveals a low specific gravity, because urine concentrating ability reduces as renal dysfunction progresses. 

As we mentioned, haematuria and evidence of urinary tract infection may also be seen on sediment examination.

If you’re concerned a UTI may be present, a cystocentesis sample should be submitted for culture and sensitivity testing, to guide antibiotic choice where required.

And what imaging do we perform in these patients?

Like many of our medical conditions, radiographs are not typically useful, especially in the early stages of disease. 

The imaging modality we prefer in these patients is ultrasound. Though we do need to bear in mind that cysts may not be visible in very small patients, in cats older than 9 months, the sensitivity of ultrasound for diagnosing CKD is above 90%.

Ultrasound can typically identify cysts 2+mm in diameter. They appear as smooth, round or irregular-shaped anechoic (black) structures. They are located throughout both the renal cortex and renal medulla, and the kidneys usually have areas of mineralisation, and poor definition between the cortex and medulla in addition to the many cysts seen.

Let’s look at genetic testing…

Genetic testing is really important in PKD patients, or when breeding at-risk breeds. Because autosomal-dominant PKD is an inherited condition, there’s no way to prevent it - except not breed from affected patients in an attempt to eliminate the condition.

PCR testing detects the PKD1 gene. Either buccal swabs or EDTA samples can be submitted for analysis; if you’re testing pre-weaned patients, a blood sample should be submitted, as nursing kittens or puppies can have traces of the mother’s DNA inside their mouths. 

Organisations such as international cat care maintain a polycystic-kidney disease negative register, where breeders can register their cats after genetic testing, so that pet parents can choose to purchase kittens from PKD-1 negative parents.

And how will we treat and nurse these patients?

We can’t do anything to treat the patient’s polycystic kidney disease - draining the cysts is not practical, since there are so many, and they will continue to refill. Instead, we manage the chronic kidney disease our patient has as a result - our focus is going to be on correcting dehydration, acidosis and hypokalaemia, providing nutritional support, administering antiemetics and other supportive medications as needed, and managing any complications associated with the patient’s renal disease - such as anaemia, hypertension, and proteinuria.

At home, we’ll get the patient’s family to continue providing supportive care, increase the patient’s water intake, and transition them to a therapeutic renal diet as needed, depending on the stage of CKD the patient has.

In terms of nursing care specific to PKD, the biggest area where we can support our patient and their families is in education.

This starts at a young age - for example, if you’re seeing an affected breed in for a puppy or kitten check, discussing potential screening. And if their pet already has evidence of PKD, they’ll need regular follow up (even in the absence of clinical signs) - with ultrasounds every 6-12 months depending on the individual, to evaluate progression of those cysts, and detect CKD at an early stage - so we can slow the progression of it as much as possible.

So that’s an overview of one of the leading causes of CKD in many of our patients - polycystic kidney disease. Though there’s nothing we can do to treat PKD itself, careful client education and communication, and regular reassessments to detect CKD at an early stage are vital. By performing genetic testing, we can not only detect patients with PKD and allow for prompt recognition of renal dysfunction, but we can also eliminate them from breeding programs, reducing the number of PKD patients in the future.

Once a patient shows clinical signs for their PKD, they’re managed as we would any other CKD patient - and as we know, there are lots of opportunities to use our nursing skills with them. From fluid therapy to nutrition, client education to renal clinics, we can make a huge difference to these patients.

Did you enjoy this episode? If so, I’d love to hear what you thought - screenshot it and tag me on instagram (@vetinternalmedicinenursing) so I can give you a shout out, and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!

References and Further Reading

Laura Jones
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