Overview

Disorder in which large portions of normally differentiated renal parenchyma are displaced by multiple cysts; renal cysts develop in preexisting nephrons and collecting ducts; both kidneys are invariably affected. In most cases the disease is inherited.

Signalment

• Persian and Persian-related breeds (e.g., Exotic Shorthair, Himalayan, Scottish fold) are affected more commonly than other breeds.
• Dog breeds affected include cairn terriers and beagles.

Signs

• Cysts often remain clinically silent until their increasing size and number contribute to renal failure or abdominal enlargement; thus patients typically are clinically normal during initial stages of cyst formation.
• May detect bosselated (lumpy) kidneys by abdominal palpation.
• Most renal cysts are not painful when palpated, but acute secondary infection of cysts may be associated with rapid distension of the renal capsule and pain.

Causes & Risk Factors

• Autosomal-dominant inheritance in Persian cats. A nucleotide transversion (cytosine to adenine) causing a premature stop codon has been strongly associated with the phenotype.
• The stimuli for renal cyst formation remains obscure; genetic, endogenous, and environmental factors appear to influence the process.
• Cystogenic chemicals include diphenylthiazole, nordihydroguaiaretic acid, diphenylamine, trichlorophenoxyacetic acid, and long-acting corticosteroids.

Differential Diagnosis

• Other multicystic diseases of the kidneys.
• Glomerulocystic disease of collies.
• Renal cystadenocarcinoma associated with nodular fibrosis in German shepherd dogs.
• Renal cysts associated with chronic renal failure or renal dysplasia.
• Non-cystic causes of renomegaly.
• Renal neoplasia.
• Hydronephrosis.
• Perirenal pseudocysts.
• Feline infectious peritonitis.
• Mycotic or bacterial nephritis.

CBC/Biochemistry/Urinalysis

• Results usually unremarkable unless patient has renal insufficiency.
• Hematuria is rare.

Other Laboratory Tests

• Genetic tests are available to identify the autosomal dominant-polycystic kidney disease (AD-PKD) type 1 mutation in cats. This test is especially useful to screen kittens less than 3–4 months old when ultrasonography may be less sensitive. The test is also useful to confirm inherited AD-PKD type 1 in breeding cats, once renal cysts are detected ultrasonographically. Other mutations may also cause inherited kidney cysts.
• Cyst fluid can be clear, cloudy, or hemorrhagic, and the fluid from different cysts in the same kidney can differ.
• Bacterial culture of cyst fluid helps in diagnosing concomitant infection.
• Hypertension is uncommon without renal failure.

Imaging

Diagnostic Procedures

Evaluation of fine-needle aspirates of the kidney may allow differentiation of cystic disease from other diseases that cause renomegaly.

Drug(s)

• Bacterial infection of cysts has been observed in cats but is rare. Unless infection is accompanied by pyelonephritis, bacteria may not be observed in urine. Consider parenchymal infection when renal cysts are associated with renal pain and fever, even in absence of bacteriuria.
• Treatment of infected cysts requires special consideration. The acidic nature of cyst fluid and its containment by an epithelial barrier might reduce bactericidal concentrations of commonly used acidic antibiotics (e.g., cephalosporins and penicillins) within cystic lumens. Alkaline, lipid-soluble antibiotics (e.g., trimethoprim-sulfonamide combinations, fluoroquinolones, chloramphenicol, tetracycline, and clindamycin), which penetrate epithelial barriers and become ionized and trapped in cyst lumens, have been recommended.

Abbreviations

AD-PKD = autosomal dominant-polycystic kidney disease