Renal Anomalies in Animals

Renal dysplasia (also called progressive juvenile nephropathy, juvenile renal disease, and familial renal disease) refers to disorganized development of renal parenchyma due to abnormal differentiation. The term renal dysplasia is sometimes used more broadly in veterinary medicine to describe congenital kidney abnormalities in young dogs for which the disease process has not been precisely characterized or otherwise differs from the pathological changes associated with renal dysplasia as defined by the National Kidney Foundation.

Renal dysplasia has been diagnosed in many common dog breeds, including Lhasa Apsos, Shih Tzu, Soft Coated Wheaten Terriers, Standard Poodles, Golden Retrievers, Cocker Spaniels, Beagles, Boxers, Miniature Schnauzers, Chow Chows, Alaskan Malamutes, Bedlington Terriers, Bernese Mountain Dogs, and Shetland Sheepdogs, as well as in less common breeds, such as Finnish Harriers and Nederlandse Kooikerhondjes. It is unclear whether the same gene is affected in all breeds with renal dysplasia or whether different gene variants exist in different breeds. In addition, renal dysplasia has been observed in puppies infected with canine herpesvirus.

Renal dysplasia is rare in cats and primarily associated with fetal infection with feline panleukopenia virus. However, this condition has been diagnosed in a Norwegian Forest Cat (1). It is also rare in lambs and horses. In pigs, it may be idiopathic or associated with vitamin A deficiency.

Renal dysplasia may be unilateral or bilateral. Animals affected bilaterally generally die in the early neonatal period, whereas animals affected unilaterally typically develop hypertrophy of the contralateral kidney.

Clinical signs of renal dysplasia, such as polyuria/polydipsia, that usually progress to clinical signs associated with uremia (eg, anorexia, vomiting, weight loss, lethargy and halitosis) are the same as those of chronic kidney disease (CKD). Dwarfing may be noticed if the onset of renal failure occurs within the first few months after birth.

Urinalysis, hemogram, serum biochemistry, and symmetric dimethylarginine (SDMA) findings are the same as those in other chronic, progressive renal diseases. Uremia is usually identified between 6 months and 2 years of age. The diagnosis is suspected based on breed and age of disease onset and is confirmed by renal biopsy.

On necropsy, affected kidneys are usually small, firm, and pale; they may have a uniformly diminished renal cortex.

Histological examination reveals disorganized parenchymal development with immature glomeruli and tubules and other features inappropriate for the animal's age. Secondary changes commonly observed include compensatory hypertrophy and hyperplasia of glomerular tufts and tubules, interstitial fibrosis, and tubulointerstitial nephritis.

Treatment is aimed at managing the associated CKD.

Renal agenesis, defined as the complete absence of one or both kidneys, is always accompanied by ureteral aplasia and may be associated with aplastic reproductive tissues on the same side.

Renal agenesis is believed to have familial predisposition in Beagles, Shetland Sheepdogs, and Doberman Pinschers. Unilateral renal agenesis is the most common congenital kidney condition in pigs; it is less common in sheep, cattle, and goats.

Clinical signs associated with unilateral renal agenesis may be absent. Bilateral renal agenesis is fatal, with the patient dying within the first few days of life.

Renal agenesis can be detected only during abdominal palpation, radiography, ultrasonography, exploratory surgery, or necropsy. The condition is typically an incidental finding, as long as the other kidney functions normally; frequently, the contralateral kidney undergoes compensatory hypertrophy.

Polycystic kidney disease is characterized by multiple cysts that progressively crowd out normal parenchyma of both kidneys.

This condition is familial in Beagles. However, an autosomal recessive condition has been identified in Cairn Terriers and West Highland White Terriers, and an autosomal dominant polycystic kidney disease has been identified in Bull Terriers.

Polycystic kidneys are an autosomal dominant inherited trait in Persian, Persian-cross, and domestic longhair cats, and hepatic cysts may also form in affected cats. Polycystic kidneys are hereditary in rabbits, ferrets, mink, rodents, and pigs and may alternatively be associated with vitamin A deficiency in pigs. Polycystic kidneys are rare in cattle and horses and very rare in sheep.

Affected kidneys are usually grossly enlarged on palpation. Cysts may not result in clinical signs or may lead to progressive decline in renal function and to eventual CKD.

Diagnosis is based on physical examination findings and on results of radiographic or ultrasonographic examination or exploratory laparotomy. Pyelonephritis may occur concurrently and precipitate renal insufficiency.

Simple renal cysts are solitary and unilocular. They generally do not communicate with the renal collecting system, and therefore the rest of the kidney is normal.

The origin of these cysts is uncertain. They are usually an incidental finding in domestic species, although occasionally they are associated with hematuria and infection.

Perirenal pseudocysts, also called perinephric cysts, are fluid accumulations that develop external to renal parenchyma. Accumulated fluid may be located between the renal parenchyma and the renal capsule or between the renal capsule and a thin-walled fibrous sac attached to the capsule. They are termed pseudocysts rather than cysts because they are not lined by epithelium.

Because only a few perirenal pseudocysts have been examined histologically, it is not known whether all perirenal fluid-filled structures are pseudocysts. The fluid contained within these structures is not urine or lymph but is described as a transudate.

Perirenal pseudocysts have been identified in cats and dogs and occur in one or both kidneys. Their cause is unknown.

Perirenal pseudocysts typically cause progressive abdominal enlargement. Abdominal palpation reveals a large, firm, nonpainful mass located in the area of the kidneys.

Diagnosis is made by excretory urography or ultrasonography. Renal function tests and urinalysis are typically normal; however, mild azotemia may occur.

Treatment involves exploratory surgery to confirm the diagnosis, drainage of the pseudocyst fluid, and resection of as much of the pseudocyst wall as possible. The prognosis is typically good; however, only a few cases have been evaluated.

Primary glomerulopathies have been identified in dogs. The best-characterized conditions involve an abnormality of type IV collagen in the glomerular basement membrane.

An autosomal recessive hereditary glomerulopathy has been identified in English Cocker Spaniels and English Springer Spaniels, and autosomal dominant inherited glomerulopathies have been identified in Bull Terriers and Dalmatians. An X-linked hereditary nephropathy has also been identified in Samoyed and Navasota mixed-breed dogs. Gene abnormalities in Soft Coated Wheaten Terriers and Airedale Terriers have also been identified, although the mode of inheritance in these breeds is complex. Doberman Pinschers, Bullmastiffs, Newfoundlands, Rottweilers, Pembroke Welsh Corgis, and Beagles develop primary glomerulopathies for which the mode of inheritance still has not been identified.

Clinically, primary glomerulopathies are characterized by the onset of persistent proteinuria that often results in progressive deterioration of renal function, azotemia, and eventual death.

Amyloidosis comprises a group of diseases characterized by extracellular deposition of amyloid proteins in medullary interstitial tissues and glomeruli. In animals in which glomeruli are affected, proteinuria and other elements of nephrotic syndrome develop. Amyloid can also deposit in other organs such as the liver.

In Chinese Shar Pei, renal amyloidosis occurs as part of an autosomal recessive condition, Shar Pei autoinflammatory disease (SPAID), although it is unclear whether this condition involves a single gene or multiple genes. Affected Shar Pei usually develop CKD; however, they may also have a history of high fever and joint swelling.

Abyssinian cats also develop renal familial amyloidosis, and the probable mode of inheritance is autosomal dominant with variable penetrance. Research is ongoing to identify genetic markers of this condition.

Unfortunately, serum amyloid A and urine protein:creatinine ratios are not helpful for early identification of affected cats.

Cystinuria in dogs is a disorder characterized by excessive renal loss of cystine in the urine. Normally, 95%–98% of cystine filtered through the glomerulus is reabsorbed in the proximal tubules. However, dogs with cystinuria have a defect in their proximal tubules that impairs cystine reabsorption, resulting increased urinary cystine excretion. Cystine is not very soluble in acidic and neutral urine, and as a result, dogs can develop cystine urolithiasis. Cystinuria can also involve impaired absorption of other dibasic amino acids, and the acronym COLA (cystine, ornithine, lysine, arginine) is a mnemonic for the other amino acids that may be involved.

Three different types of cystinuria have been identified in dogs. Type 1 cystinuria is an autosomal recessive hereditary disorder linked to either the rBAT gene or the SLC3A1 gene. It is most commonly seen in Newfoundlands, Labrador Retrievers and Landseers. Type 2 cystinuria is an autosomal dominant hereditary disorder associated with either the SLC3A1 gene or the SLC7A9 gene. It is most commonly seen in Australian Cattle Dogs and Miniature Pinschers. Type 3 cystinuria is an androgen-dependent cystinuria that is seen most commonly in English bulldogs, French bulldogs, and English mastiffs; however, the genetics associated with this type of cystinuria are poorly understood. Neutering may be important when trying to manage type 3 cystinuria, but neutering does not appear to be effective treatment for type 1 or type 2 cystinuria. However, neutering should still be encouraged with types 1 and 2 cystinuria because it is a hereditary disorder.

Other breeds of dogs predisposed to cystinuria include Pembroke Welsh Corgis, Cardigan Welsh Corgis, and miniature Dachshunds.

Cystinuria also occurs in cats and involves multiple genes. Besides the urinary tract signs that occur from cystine urolithiasis, cats with this condition may also develop neurological signs associated with hepatic encephalopathy and high serum ammonia levels. Cats have a higher dietary arginine requirement than dogs and need arginine for the urea cycle to function. Cats with cystinuria have impaired renal reabsorption of arginine and may develop hyperammonemia and neurological signs as a result of arginine deficiency.

Putatively familial immune-mediated glomerulonephritis occurs in Soft Coated Wheaten Terriers, Bernese Mountain Dogs (likely autosomal recessive), and Brittany Spaniels (autosomal recessive). Fanconi syndrome is observed in Basenjis.

Other congenital defects include renal malpositioning, renal fusion, and nephroblastoma. Renal malpositioning can occur in dogs, cats, swine, and cows, while renal fusion has been reported in both dogs and cats. Nephroblastoma is an embryonal tumor that is rare in domestic animals except pigs. It may not cause any problems but may be very large and result in abdominal distention.

1. Aresu L, Zanatta R, Pregel P, et al. Bilateral juvenile renal dysplasia in a Norwegian Forest Cat. J Feline Med Surg. 2009;11(4):326-329. doi:10.1016/j.jfms.2008.08.004