Feline Polycystic Kidney Disease

Margie Scherk, DVM, DABVP (Feline Practice), catsINK

ArticleLast Updated September 20147 min readPeer Reviewed
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Figure 1, main image: Necropsy of both sectioned kidneys from a cat with PKD; note fluid-filled cysts of varying sizes and obliteration of large portions of both the cortex and medulla. Only scant amount of renal parenchyma (pink) remains. Image courtesy of Dr. Susan Little.

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Definition

  • Polycystic kidney disease (PKD) is the most common inherited renal disease of cats.1

  • PKD is one of the leading causes of chronic kidney disease (CKD) in Persians and related breeds.2

  • PKD progresses slowly as portions of the cortex and medulla are replaced by cysts (Figure 1). 

  • Cysts compress functional parenchyma as they enlarge, thus decreasing kidney function.

  • Cyst number and rate of growth are highly variable.2

Systems

  • Kidneys ± liver and/or pancreas1,3-6

Genetic Implications

  • Autosomal dominant (AD) mode of inheritance with variable penetrance

  • Affected cats are heterozygotes; homozygous expression is embryonic lethal.7,8

  • Mutation in PKD1 gene leads to a C>A transversion in exon 29, leading to a stop codon.

  • This is the basis for genetic testing.<sup7-9 sup> 

  • Variable expression is seen in related and unrelated individuals. 

  • Cyst size and number varies from cat to cat and parent to offspring. 

  • Mildly affected queens can produce offspring with severe disease and vice versa.2

Incidence & Prevalence

  • Affects approximately 6% of cats.

  • May affect up to 37%–50% within Persians and related breeds.10-13

  • In other breeds, prevalence may be as high as 16%.14

Geographic Distribution

  • Worldwide

Signalment       

Breed Predilection15

  • High risk: Persian, Himalayan, exotic shorthair breeds, British shorthair breeds

  • Moderate risk: Asian, Birman, Bombay, Burmilla, Cornish rex, Devon rex, ragdoll, Snowshoe, Tiffanie

  • Low risk: Abyssinian, Angora, Balinese, Bengal, Burmese, Chartreux, Egyptian Mau, Korat, Maine coon, Norwegian forest cat, Ocicat, Oriental longhair, Oriental shorthair, Russian blue, Siamese, Singapura, Somali, Tonkinese, Turkish van

  • Cystic renal disease occurs with a low prevalence in the Maine coon and is unrelated to the PKD1 mutation observed in Persians and related breeds.16

  • Despite conscientious warnings and screenings by breeders, the ragdoll has a low prevalence of PKD (<3%).17,18

Age & Range

  • Affected cats usually develop CKD signs between 3–10 years of age (mean, 7 years).

Sex

  • No sex predilection

Pathophysiology

  • Polycystin-1, encoded by the PKD1 gene, is a renal tubule membrane glycoprotein needed for epithelial cell proliferation and differentiation.

  • Substitution of a cytosine base for an adenine base results in insufficient polycystin-1 production. 

  • Insufficient polycystin-1 results in tubule remodeling and cyst formation.

  • Cysts may develop in the embryo.*

  • This is under investigation.  

  • Stress may cause CKD manifestation in predisposed individuals.19

  • One study showed increased mean arterial pressures and aldosterone: renin ratios20; one therapeutic case series showed no resolution of hypertension after surgical drainage.21

  • However, PKD does not result in hypertension in cats as it does in humans and dogs.22

  • Cats that develop CKD secondary to PKD may be at risk for hypertension.

History & Clinical Signs

  • Many cats remain subclinical for an extended time.

  • History and clinical signs are those typical of CKD:

  • Polyuria, polydipsia, dehydration, lethargy, inappetence/anorexia, nausea/vomiting, constipation, weight loss, muscle wasting, and oral ulceration

  • Cysts may also result in hematuria and increased risk for urinary tract infections.23

  • Cats with large cysts have irregular, large kidneys. 

  • Cysts are often bilateral.

  • Patients may present with signs associated with liver disease, albeit rarely. 

  • 6%–68% of affected cats have hepatic cysts.4,24

  • Rarely, hepatic encephalopathy may be present with hepatic cysts and fibrosis.25,26

Table: PKD Differential Diagnosis

 

Cause

Imaging Findings

Prognosis

PKD

AD mutation of PKD1 gene

Multiple, variably sized cysts in both kidneys ± hepatic, pancreatic cysts

Because of variable progression, some cats remain asymptomatic while others develop CKD rapidly 

Perinephric pseudocysts

Numerous causes (eg, trauma, perirenal fat necrosis, neoplasia, idiopathic) 

Fluid-filled sac surrounding one or both kidneys; fluid accumulates between renal capsule and parenchyma

Reduction of pressure by ultrasound-guided drainage or surgical resection or fenestration ± omentalization has good outcome depending on degree or age of compression-induced CKD

Acquired cysts

Intraluminal tubular obstruction by inflammatory debris; extraluminal compression of tubules by parenchymal inflammation or fibrosis

Unilateral or bilateral, variably sized and located cysts

Compression-induced CKD progresses with rate depending on severity of lesion

Diagnosis

Definitive Diagnosis

  • CBC, serum chemistry, and urinalysis are required for CKD diagnosis.

  • Ultrasonography and genetic testing are required to definitively diagnose PKD.

  • Cats may not have the same genetic mutation.27

  • Cysts may not be visible in very young cats.27

  • Genetic testing identifies only the AD form of PKD, not other forms of cystic kidney disease.

  • Ultrasonography is sensitive for PKD detection, assesses severity, is repeatable, and is useful for monitoring disease progression.28

Differential Diagnosis

  • Renomegaly: Lymphoma, feline infectious peritonitis granulomatous nephritis, perinephric pseudocysts, acquired renal cysts, hydronephrosis, acromegaly 

  • See PKD Differential Diagnosis

Laboratory Findings

  • Depending on CKD stage, increases in BUN and creatinine, low urine-specific gravity secondary to decreased concentrating ability, alterations in electrolytes, and anemia may be present.

Figure 2: Ultrasound image of a polycystic kidney in a young Himalayan cat with multiple hypoechoic cysts.

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Imaging

  • Radiography is not useful in early stages.

  • Once large cysts are present, renomegaly and asymmetry of renal size will be apparent ± dystrophic calcification.

  • Ultrasonography can typically identify renal cysts >2 mm in diameter (Figure 2).

  • Diagnostic sensitivity of ultrasound is 91% in cats >9 months of age.27

  • Phenotypic variation in cyst size and number is considerable.

  • Cysts are smooth, round, or irregular anechoic structures of variable size located throughout the renal cortex and medulla and grow over sequential assessment.2,29

  • Affected kidneys have indistinct corticomedullary junctions and foci of mineralization.3,29

  • Absence of cysts at youth does not guarantee the cat will not develop them later.

  • Cysts may be found as early as 6–8 weeks of age.      

  • False negatives at this age are a result of small cysts or operator inexperience.

  • Kittens from affected lines should be screened at ~10 months of age.<sup3 sup>

Genetic Testing (PCR)

  • Detects PKD1 gene

  • Useful for early diagnosis in potential breeding stock

  • Buccal swab can be used in very young kittens.

  • Care must be taken if the kitten is not weaned; milk may contaminate the sample.

  • In preweaned or older cats, blood sample may be used in lieu of buccal swab.

  • Several tests are available.7,8

Postmortem Findings & Histopathology

  • Cysts are focal dilations of the renal tubules.

  • Varying amounts of normal renal parenchyma remain surrounded by fibrous tissue.

Treatment

Medical

  • No definitive cure; condition is inherited, irreversible, and progressive.

  • Therapy reflects IRIS stage (iris-kidney.com) with in-hospital or home fluid therapy, potassium supplementation, phosphate binders, H2-receptor antagonists, antiemetics, appetite stimulants, and erythropoietin as needed.

  • When present, CKD hypertension should be managed with amlodipine.

  • When present, proteinuria should be managed with benazepril or telmisartan (eg, an angiotensin receptor blocker).

  • Urinary tract infection must be treated with appropriately sensitive antimicrobials to prevent secondary cyst infection and sepsis.

  • Analgesics may be warranted.

Surgical

  • Cyst drainage fails to slow progression but may reduce discomfort.

  • Ultrasound-assisted drainage and alcoholization has been evaluated.21

Nutritional

  • If muscle wasting is not present, a renal diet may be considered after IRIS Stage 3.

  • Appetite stimulants may be beneficial; caloric and protein requirements should be calculated.

  • Short-term feeding tubes may ensure adequate nutrition is received.

Client Education

  • Knowing which cats are affected allows for planned mating to reduce PKD.

  • All Persians and related cats and cats with known familial risk should be screened.

  • Combining ultrasound with genetic testing improves diagnostic yield.

  • Some cats with cystic kidney disease are not PKD1 positive and do not have PKD.

  • Complete elimination of all affected Persians from breeding programs would reduce the diversity of the breed and may lead to other undesirable characteristics.

  • Mating an affected progenitor with a healthy individual results in 50% of descendants being disease free; this type of crossing helps avoid losing a genetic line while conserving genetic diversity.

Follow-Up

Patient Monitoring

  • Cats with PKD should be monitored q6–12mo via ultrasound to evaluate cyst progression and detect changes indicating supportive care for emerging CKD.

  • Once CKD is present, cats should be monitored as often as is indicated.

In General       

Relative Cost

  • Diagnostics:

  • Ultrasound: $$

  • Genetic testing (PCR): $

  • CKD treatment: $$–$$$$$

Prognosis

  • If minimally affected: Good

  • If rapidly progressive: Poor

Prevention

  • Affected individuals should be identified to enable planned breeding.

General Comments

*Personal correspondence with Leslie Lyons, MS, PhD; August 2014