An inherited disorder characterized by the presence of multiple fluid filled cysts within the renal cortex and medulla, and occasionally also within the hepatic parenchyma.
Autosomal dominant polycystic kidney disease (AD-PKD) is the most common inherited renal disease of cats and is a common condition in Persian and Exotic Shorthaired cats. In most cats it occurs due to an autosomal dominant mutation of the PKD1 gene.
Affected cats can be identified by a gene test (cats of any age) or ultrasound scanning of the kidneys (cats over 10 months of age).
The International Cat Care AD-PKD Negative Register International Cat Care AD-PKD negative register allows breeders and owners to find cats that have been gene tested and are negative, encouraging the development of controlled breeding plans aimed at eliminating the condition.
Cause: autosomal dominant inherited disorder causing multiple, congenital renal cysts which enlarge with age; acquired renal cysts occur rarely, usually in small numbers.
Signs: initially asymptomatic, progressing at an unpredictable rate to chronic renal failure.
Advancing to chronic renal failure Kidney: chronic kidney disease with lethargy, anorexia, polyuria, polydipsia, constipation, weight loss, muscle wastage and possibly vomiting.
Cysts may result in hematuria and risk of urinary tract infections.
Enlarged, irregular kidney(s) on abdominal palpation. Cysts are often bilateral.
Cysts are congenital.
Cysts enlarge with age at an unpredictable rate, eventually causing kidney disease. Kidney disease may develop as young as 2 or 3 years of age, or may not occur until into old age. The mean age when cats develop signs of chronic kidney disease is 7 years.
Very common in Persians Persian longhair and Exotic Shorthairs Exotic Shorthair; affects approximately one third of cats of these breeds in the UK, and around the world.
Cystic renal disease occurs with a low prevalence in the Maine Coon Maine Coon and is unrelated to the PKD1 mutation seen in Persians and related breeds.
Polycystin-1 is a renal tubule membrane glycoprotein required for epithelial cell proliferation and differentiation. It is encoded by the PKD1 gene. Insufficient polycystin-1 production causes remodelling of renal tubules and cyst formation.
AD-PKD is an autosomal dominant condition inherited on a single gene meaning that:
All cats with the abnormal gene have AD-PKD (healthy carriers do not exist).
Only one parent of an affected cat needs to be affected.
Every cat with AD-PKD will pass the disease to a proportion of its kittens (even if the other parent is unaffected).
Renal cysts may be due to microbes, drugs, toxins, etc. These diseases occur rarely in cats.
Autosomal dominant polycystic kidney disease is an inherited condition causing the development of multiple cysts in renal tissue.
Cysts are present from birth. Cats are initially asymptomatic, however the cysts gradually enlarge displacing normal renal parenchyma. Subsequently, substantial tubulointerstitial inflammation and/or fibrosis occurs in surrounding tissue resulting in chronic kidney disease and kidney failure.
Severely affected individuals may succumb at an early age, eg 2-3 years old, other cats maintain adequate renal failure into old age.
The "average" age quoted for development of renal failure is 7 years of age, but there is enormous variability between individuals.
No clinical signs in early stage of disease.
Weight loss, poor appetite.
Some affected cats may develop abdominal enlargement.
Possibly constipation, vomiting.
Cysts may result in hematuria and risk of urinary tract infections.
Renal enlargement, most commonly bilateral.
Irregular kidney surface (loss of normal bean shape).
Rarely patients may present with signs associated with liver disease (6-68% of affected cats have hepatic cysts).
Enlarged kidney with irregular surface, loss of normal bean shape.
Multiple round, well-demarcated, thin-walled anechoic to hypoechoic areas within the cortex or medulla of the kidney:
Ultrasonography can identify cysts >2 mm in diameter. Cysts may be very small, around 1 mm diameter, in the early stages of disease .
Affected kidneys may have reduced corticomedullary definition and may have mineralised foci.
Cysts maybe present in other abdominal organs, eg liver/biliary tree.
In advanced disease, cysts are large and diagnosis is relatively simple.
Ultrasound scanning by experienced sonographers, using a high definition ultrasound probe is more than 95% accurate for detection of disease in cats over 10 months of age.
Cats under 10 months of age or those that are to be used for breeding should be screened using the gene test.
Identification of the gene (PKD1) that causes autosomal dominant AD-PKD has led to the development of a gene test. Developed initially by Veterinary Genetics Laboratory (VPL) in California, the gene test has shown excellent agreement with the results of ultrasound screening Internation Cat Care AD-PKD negative register.
The test is now available in the UK via Langford Veterinary Diagnostics and the Animal Health Trust, Newmarket.
The test can be run using cells collected from the mouth (buccal mucosal swab) or on a blood sample.
Animals can be tested at any age. Buccal swabs are not recommended for testing suckling kittens as they may be contaminated with maternal DNA.
All other tests are only able to detect disease once renal failure is present.
Analysis of cystic fluid:
Aspiration of cystic fluid may cause iatrogenic infection of the renal cysts.
Clear, odorless fluid, without detection of hemorrhage or infection on sediment examination.
Cysts fail to opacify on intravenous urography. Intravenous urography Radiography: intravenous urography is not without risk and may result in induction of dehydration, progression of kidney disease and rare anaphylactic shock.
Kidney biopsy Biopsy: kidney is rarely indicated, especially in affected Persian and Exotic Shorthaired cats. Histopathology may help to differentiate acquired and hereditary renal cysts. The possible complications of this biopsy should be seriously considered, because of the limited additional information gained by histopathology.
A kidney diet may be considered after IRIS stage 3.
Phosphate binding agents should be considered if dietary therapy alone is not successful in managing hyperphosphatemia Hyperphosphatemia.
Appetite stimulants (eg mirtazapine) may be useful in cats with reduced appetite.
Erythropoeitin stimulating agents (eg darbopoeitin) may be useful in cats with moderate to severe anemia of renal disease.
Ultrasound guided drainage of cysts and/or alcoholization fails to slow disease progression but may reduce discomfort associated with capsular stretch.
Antibiosis if cysts have become infected - lipid soluble antibiotics, eg trimethoprim Trimethoprim, clindamycin Clindamycin, tetracycline Tetracycline because they penetrate the cyst. Antibiosis may also be required if evidence of urinary tract infection exists.
Monitor renal function.
Monitor for complications of chronic kidney disease:
Avoid breeding from lines producing affected individuals. The International Cat Care AD-PKD Negative Register allows breeders and owners to identify cats that have been tested and found to be negative.
Perform gene testing or ultrasound screening of all Persian and Exotic Shorthaired cats before they are used for breeding.
Consider ultrasound screening of breeding animals from other cat breeds that have used Persian blood-lines in their development, eg Burmilla, British Short-haired British shorthair, Maine Coone Maine Coon.
Poor: progressive disorder causing chronic kidney disease in the majority of affected animals however many cats remain asymptomatic for long periods and some cats may never show clinical disease. If signs of kidney disease are rapidly progressive, the prognosis is poor.
Good: in cases of acquired renal cysts if there is no underlying progressive kidney disorder.
Expected response to treatment
Improved quality of life.
No effect on rate of progression of disease; once cats with AD-PKD develop signs of chronic renal failure they often deteriorate relatively rapidly.
Reasons for treatment failure
Disease progression will result in deterioration of kidney function.
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Other sources of information
Biller D S (1994) Polycystic kidney disease.In:Consultations in Feline Medicine 2.Ed. J R August. W B Saunders. pp 325-330.