Congenital disease of the urinary system

Renal dysplasia is malformation of the kidney. It is more common in the following breeds – Alaskan Malamutes, Bedlington Terriers, Chow Chows, Cocker Spaniels, Doberman Pinschers, Keeshonden, Lhasa Apsos, Miniature Schnauzers, Norwegian Elkhounds, Samoyeds, Shih Tzus, Soft-coated Wheaten Terriers, and Standard Poodles. Renal dysplasia may be unilateral or bilateral. This usually presents as early onset renal failure.

Polycystic kidneys can be identified on ultrasound by the formation of multiple cysts. There may be no symptoms or progressive renal failure. This is seen more commonly in the following breeds – Beagles, Cairn Terriers, Persian cats, and domestic long-haired cats.

Ectopic ureter occurs when the ureter opens into the urethra, uterus or vagina instead of the bladder. It is 8 times more common in female dogs than males and usually presents around 6 months of age. There is a genetic component in the flowing breeds – West Highland White Terriers, Fox Terriers, and Miniature and Toy Poodles and a familial occurrence in Siberian Huskies and Labrador Retrievers.

Patent uracus
is the remnant of the embryonic urinary tract. In the womb urine is collected in the fetal membranes not the bladder and passes out through the umbilical cord. If the uracus does not close off; urine is excreted through the umbilicus. This is corrected surgically.

Urethrorectal fistulas occur in English Bulldogs. There is a connection between the urethra and rectum. Urine is passed from both orifices and urinary infections are common.

Treatment of kidney disease

Kidney disease is the third most common cause of non-accidental death in dogs, and the second most common in cats. Because 75% of the kidney function is lost before we see symptoms we often do not diagnose kidney disease until it is too late. Blood and urine tests performed once or twice a year will identify kidney disease long before the owner notices symptoms. Creatine and urea (Blood urea nitrogen) are waste products from protein breakdown, their levels are elevated in kidney disease. With chronic disease blood proteins may be lowered and anemia develops. The most sensitive test is the ERD, early renal detection which can identify microscopic amounts of urine leaking from the kidneys.

Kidney disease can be caused by trauma, toxins, infection, inflammation, autoimmune disease, drug reactions, tumors and urethral obstruction. Ultrasound and biopsy are required to make a definitive diagnosis. The treatment of acute renal disease is more specific but has much in common with the treatment of chronic kidney failure:

  • Fluid therapy is the corner stone of treatment. The fluids flush the toxic waste products out of the body.
  • Diet – Low protein and low phosphorus. A low protein diet with a high biological value is fed. This reduces the build up of toxic waste products from protein break-down. High phosphorus in the diet speeds up kidney failure and low phosphorus slows it down. Salt should be restricted. Hills Canine and feline k/d™ are recommended for patients with kidney disease.
  • Vitamin supplementation (B & C) water soluble vitamins are flushed from the body in animals with kidney disease. Diets should contain additional amounts of these vitamins.
  • Treatment gastric ulceration; the toxins that build up in the blood cause gastric ulceration. If the patient is vomiting cimetidine and sucralfate should be given to reduce gastric ulceration.
  • Antibiotics are given to prevent build up of bacteria. The high urea levels in the blood provide “food” for bacteria. Dogs and cats with kidney disease are prone to infection.

  • Erythropoietin can be given to correct the anemia that develops because the kidneys are not producing enough
    erythropoietin
  • Potassium replacement may be required in patients who are loosing it because of the large volumes of urine they
    produce.

Urolithiasis

The urine contains dissolved minerals. These minerals can combine together to form crystals. These crystals can grow till they are big enough to see with the naked eye. At this point they are called uroliths (calculi or stones). Uroliths can develop anywhere within the urinary tract but are most common in the bladder. The uroliths have a small organic center and are often related to urinary infection. There are about ten different minerals found in uroliths as you can see from the following table.

Mineral name Chemical formula Chemical name
Struvite MgNH4PO4•6H20 Magnesium ammonium phosphate hexahydrate
Whewellite CaC2O4•H20 Calcium oxalate monohydrate
Weddellite CaC2O4•2H20 Calcium oxalate dihydrate
Hydroxyapatite Ca10(PO4)6(OH)2 Calcium phosphate (hydroxyl form)
Urate C5H4N4 O3 Urate
Ammonium urate NH4•C5 H4N4O3 Ammonium urate
Sodium urate Na•C5H4 N4O3 × H2 O Sodium urate monohydrate
Cystine (SCH2CHNH2 COOH) 2 Cystine
Silica SiO2 Silica
Xanthine C5H4N4 O2 Xanthine

Uroliths are produced when sufficiently high urine concentrations of urolith-forming constituents exist and the crystals remain within the urinary tract for a long enough period. For common calculi (eg, struvite, cystine, urate), other favorable conditions (eg, proper pH) for crystallization must also exist. These criteria can be affected by urinary tract infection, diet, intestinal absorption, urine volume, frequency of urination, therapeutic agents, and genetics.

The most common sign of uroliths is no sign. Most crystals are picked up on routine urinalysis. Clinical signs may relate to bladder infection – cystitis, pain or difficulty on urination – dysuria, hematuria or inability to urinate – stranguria. If the crystals obstruct the urethra urine builds up in the bladder causing acute renal failure and if left untreated death. Urethral obstruction is more common in male dogs and cats because the urethra is longer and narrower. This condition is a surgical emergency. The bladder should be drained, IV fluids antibiotic and painkillers are given to stabilize the patient before removal of the stones.

Struvite stones are the most common and often are associated with concurrent bladder infection. They form in urine with a high pH. Bacteria in urinary infections increase pH and predispose to struvite formation. The bacteria excrete urease, this enzymes breaks down the urea in urine providing more building blocks for phosphate compound. High protein diets result in more urea in the urine and can contribute to urolith formation. Treatment involves antibiotics to remove infection for 10 – 14 days plus a diet to reduce urinary pH and phosphate levels. Urinalysis should be repeated after 4 weeks. If therapy is not dissolving the stones or they are very large then surgical removal will be necessary.

Radiograph showing struvite bladder stones

kidneys_5

Oxalate stones form in an acidic urine pH 6.8 – 7. These stones cannot be dissolved by diet but can be prevented. Diet should be lower in protein and salt. This will reduce the amount of calcium and oxalate in the urine and the pH should be alkaline. Some drugs predispose to oxalate stone formation; cortisone, frusemide and urinary acidifiers such as vitamin C. Oxalate stones are more common in adult male small breed dogs. Calcium oxalate stones are not usually associated with cystitis.

Urate stones are seen in Dalmatians and dogs with porto-caval shunts.

FUS/FLUTD

Feline urological syndrome or feline lower urinary tract disease is a catch all term for urolithiasis, infection and inflammation of the bladder and urethra in the cat. FUS affects 30% of cats in their lifetime. It starts between 2 and 6 years of age and recurs throughout life. Predisposing factors include stress, low water intake, urine pH and a high ash content in the diet. Many cats will present with increased frequency of urination, hematuria, dysuria, urinating outside the litter box and behavioral changes. Although when analyzed the urine has no bacteria cats often respond well to antibiotics. Dietary modification, urinary acidifiers and NSAIDS are used to treat FUS.

Struvite stones used to be the most common in cats due to the formulation of commercial cat foods. Calcium oxalate is the now most common urolith in cats. Once these stones have formed they cannot be dissolved and have to be surgically removed. Diets that are lower in magnesium and produce an acid pH help prevent the formation of struvite but this may be contributing to higher incidence of oxalate stones. Struvite dissolving diets reduce the pH to less than 6.0, have lowered amounts of magnesium and added sodium chloride to increase water intake.

Urinary diets

When crystals are detected in the urine we will give a course of antibiotics and start the patient on a prescription diet. Hills canine c/d™, s/d™, or u/d™,. These diets are formulated to reduce the level of minerals in the urine and change the pH to prevent crystals forming. Hills Canine s/d™ is used to dissolve struvite stones, then Hills c/d™ is used for maintenance. Canine u/d™ is used to control oxalate, urate, cystine and silicate urolithiasis. Hills Feline s/d™ is used to dissolve struvite stones it is available in cans and dry. Hills c/d™ Multicare feline is indicated for Feline Lower Urinary Tract Disease : cystitis, Struvite Urolithiasis and Calcium Oxalate Urolithiasis. It is available in different flavors, canned and dry. A repeat urinalysis should be performed a month after starting the diet.

Incontinence

Incontinence is the inability to control urination. The neck of the bladder and urethra consist of a layer of muscle tissue. This ring of muscle is called the urethral sphincter and it controls urination. Incontinence can be caused by anatomical defects, nerve dysfunction and muscle weakness.

  • 1. In young animals incontinence can be caused by ectopic ureters, the ureter bypasses the bladder and the sphincter and enters straight into the urethra or vagina, the urine dribbles out constantly.
  • 2. Damage to the nerves controlling the sphincter can cause incontinence. Nerve damage can take two forms; if the sphincter is constantly open then urine leaks out and the bladder is small; if the sphincter is closed the bladder is full and eventually pressure forces some urine out – retention and overflow. Where incontinence is caused by retention and overflow the bladder must be drained regularly to prevent kidney damage. Nerve damage is often caused by spinal trauma – hit by car or disc disease and in cats pulling/fracture of the tail.
  • 3. In older dogs, usually bitches, the sphincter muscle can become weak and some urine will leak when the bladder is full or the dog is lying down. At other times the dog will urinate normally. This can be treated with estrogens or phenylpropanolamine (Proin or Propalin) which increase the strength of the sphincter muscle.