Chapter 12 Diseases of the Urinary System

Anatomically, the urinary system is composed of the kidneys, ureters, bladder, and urethra (Fig. 12-1). The main job of the urinary system is waste removal, although it is also instrumental in red blood cell production, the regulation of water and electrolyte balances, and control of blood pressure. The system is a blood plasma balancer. It processes blood plasma by adjusting the water and electrolyte content, removes waste materials not needed by the body, and returns those necessary substances to the systemic circulation. It also regulates the pH of the plasma. The final product is urine, which is stored for elimination.

Figure 12-1 The urinary system is made up of two kidneys, two ureters, one urinary bladder, and one urethra.

(From Colville T, Bassert JM: Clinical anatomy and physiology for veterinary technicians, St Louis, 2002, Mosby, by permission.)

The kidneys are located in the retroperitoneal space along the vertebral column from T13-L3. Internally, the kidney is divided structurally into the cortex (the outer region) and the medulla (the inner region) (Fig. 12-2). The “filtration units,” or glomeruli, are concentrated in the cortical region, whereas the “concentration/exchange tubules,” or nephron loops, are found in the medulla (Fig. 12-3). Blood enters the kidney and is filtered through the capillaries of the glomerulus. The nephron loop concentrates the filtrate and reabsorbs vital nutrients. The urine passes into the ureters and then on to the bladder for storage before elimination.

Figure 12-2 Frontal section of right kidney.

(From Colville T, Bassert JM: Clinical anatomy and physiology for veterinary technicians, St Louis, 2002, Mosby, by permission.)

Figure 12-3 Fluid flow through the nephron.

(From Colville T, Bassert JM: Clinical anatomy and physiology for veterinary technicians, St Louis, 2002, Mosby, by permission.)

Clinical disease can result when any portion of this system fails to function properly. The most commonly seen clinical problems involving the urinary system include cystitis, cystic calculi, urinary obstruction, acute and chronic renal failure (CRF), and incontinence.

CYSTITIS

Feline Cystitis (Idiopathic [Interstitial] Cystitis)

Feline cystitis (idiopathic cystitis) is a nonmalignant inflammatory condition, previously known as feline urologic syndrome or feline lower urinary tract disease, that occurs frequently in cats. In a study at Ohio State University of 132 cats examined for symptoms of irritative voiding (dysuria, hematuria, and pollakiuria), 61% were found to have idiopathic cystitis. The cause for this disease is unknown, although a virus may be the causative agent. The disease appears to be self-limiting in most cats, with clinical signs subsiding within 1 week to 10 days. Any treatment appears to help because of the self-limiting nature of the cystitis.

Cats with undocumented bacteriuria should not be treated with antibiotics. Needless antibiotic treatment only results in an increased number of antibiotic-resistant organisms.

Change of diet may be the most beneficial treatment, especially if it results in dilute urine without an increase in urine pH. If possible, cats should be fed canned food or have water added to their dry food.

Cats should be given places to hide; toys and scratching poles allow cats to exercise normal play behavior and reduce stress, which has been shown to help in the treatment of this disorder.

Use of amitriptyline is advocated to reduce pain and decrease clinical symptoms. A dose just sufficient to calm the cat is given orally once daily at bedtime. Monitor liver enzymes while the cat is receiving this medication.

CLINICAL SIGNS

• Hematuria (frank blood or a pink urine)

• Dysuria (pain on urination)

• Inappropriate urination (e.g., floors, sinks, bathtub)

• More frequent urination (small volumes)

DIAGNOSIS

• Urinalysis: Both dipstick and sediment examination should be performed to rule out bacterial cause or systemic disease.

• Urine culture is negative.

• Radiographic contrast studies may indicate irregular mucosal lining and thickened bladder wall, or radiographs may be normal.

TREATMENT

• Avoid unnecessary use of antibiotics unless urinalysis indicates a bacterial cause.

• Change diet to produce dilute urine.

• Provide amitriptyline to relieve clinical signs and ease discomfort.

• Antiinflammatory medications should be used with caution. (There have been no positive clinical effects seen in controlled studies.)

• Administer propantheline orally (PO) every 72 hours to relieve incontinence until the condition resolves.

INFORMATION FOR CLIENTS

• This disease is self-limiting.

• This may be a recurring problem.

• There is no definitive cure.

• Reduction of stress in the cat’s environment helps prevent recurrence.

• It may be difficult to change the diet. Be creative and patient.

Canine Cystitis (Bacterial Cystitis)

Although bacterial urinary tract infection accounts for only 1% to 3% of all feline cystitis, it is the most common cause of cystitis in the dog. The urinary tract is normally sterile (free of bacteria) and resistant to infection. Natural defense mechanisms such as frequent voiding of urine, urethral and ureteral peristalsis, glycosaminoglycans in the surface mucosal layer, pH, and constituents of the urine assist in preventing the invasion of bacteria into lower urinary tract structures.

Urinary tract infections are most commonly the result of ascending migration of bacteria up the urethra. The blood-borne route does not seem of much importance in animal infections. The motility of some bacteria such as Escherichia coli and Proteus spp. may assist in this migration. Once in the bladder, the microorganisms must adhere and colonize the mucosal lining. Bacteria that may be nonpathogenic in the healthy animal may be virulent in hosts with altered immunity.

CLINICAL SIGNS

• Increased frequency of urination

• Hematuria

• Dysuria

• Cloudy urine, abnormal odor

• Frequent licking of the urethral area

DIAGNOSIS

• Urinalysis: Dipstick and sediment examination show increased white blood cell (WBC) counts and bacteria.

• Urine culture and sensitivity: Collect by cystocentesis and culture within 30 minutes for best results. This should always be done.

TREATMENT

Prevention

• Avoid unnecessary use of indwelling urinary catheters.

• Use a closed system when using indwelling urinary catheters (Fig. 12-4).

• Avoid trauma to the urinary tract during surgical procedures.

• Select the least expensive, least toxic, most effective antibiotic to start treatment. Because of frequency of urination, it is recommended to dose the drug every 8 hours when possible. Treatment should be of sufficient duration to eliminate the bacteria.

• Treatment for acute infections should be for 10 to 14 days. Chronic or relapsing infections require 4 to 6 weeks of treatment.

Figure 12-4 Collection apparatus in place for continuous urine drainage. Note that collection container is below the level of animal’s urinary bladder.

Antibiotics

• Choice should be based on culture and sensitivity results.

• Empiric choice of antibiotics: Drug should attain effective concentrations in the urine and tissue. Some good choices include the following:

Ampicillin: PO every 8 hours

Amoxicillin trihydrate (clavulanate potassium): PO every 8 hours

Trimethoprim-sulfonamide: PO every 12 hours

Cephalexin: PO every 8 to 12 hours

Enrofloxacin: PO every 12 hours

INFORMATION FOR CLIENTS

• Most uncomplicated urinary tract infections resolve without treatment.

• If antibiotics are needed, make sure you give them as directed and for the prescribed time period to avoid creating resistance to the drug.

• Relapses are common (many relapses are due to inadequate treatment).

• The prostate may be the source of recurring infections in male dogs.

• Repeat cultures during treatment to follow progress.

FELINE UROLITHS AND URETHRAL PLUGS

A detailed description of feline uroliths is beyond the scope of this text. Students are referred to veterinary medical texts for more information.

“Plugged” cats are a frequent occurrence in the small-animal hospital. The inability to pass urine may have serious and even fatal consequences. Two common causes of urethral obstruction in the cat are uroliths and urethral plugs. These terms should not be used synonymously because they are physically distinct from one another. Uroliths are polycrystalline concretions composed of minerals with a small amount of matrix. Urethral plugs consist of small amounts of minerals in a large amount of matrix. This section discusses each of these as they affect urinary tract disease in the cat.

Feline Uroliths

A number of different minerals can be found in feline uroliths (Fig. 12-5). These include the following:

• Struvite (approximately 60%)

• Calcium oxalate (27%)

• Ammonium urate (5.5%)

• Cystine

• Mixed mineral

Figure 12-5 Various types of crystals that may be found in urine.

(From Hendrix CM, Sirois M: Laboratory procedures for veterinary technicians, ed 5, St Louis, 2007, Mosby, by permission.)

Uroliths, also called bladder stones, may be located anywhere in the urinary tract. Some are radiopaque and are easily diagnosed by radiographs (e.g., calcium oxalate, urates, and struvites), whereas others are radiolucent and require double-contrast cystography to be seen.

In most cases, the cause of urolith formation cannot be determined, although studies show that diets high in magnesium produce struvite uroliths experimentally in cats. Obese, older cats (>2 years) appear to be predisposed to urolith formation. There appears to be no breed predisposition for struvite uroliths; however, Burmese, Himalayan, and Persian breeds have a greater prevalence of calcium oxalate uroliths. Cats that form uroliths typically have concentrated urine with altered pH (either too alkaline or too acidic). Cats with uroliths may be asymptomatic or may present with signs of lower urinary tract disease or urethral obstruction. Spontaneous reabsorption of uroliths has been documented.

Uroliths that remain in the bladder can damage the bladder lining, resulting in secondary bacterial infections and hematuria. Small uroliths that become lodged in the outflow tract present a special problem. As urine flow out of the bladder stops, the bladder distends with urine. This results in a backup of urine through the ureter and into the kidney, virtually halting renal filtration and urine production. The cat becomes azotemic within 24 hours, and clinical signs relating to this begin to be evident at this time. If the obstruction to urine flow is not relieved within 3 to 6 days, the cat will die.

This section focuses on struvite uroliths because they are the most commonly seen type. Please refer to medical texts for treatment of other types of uroliths.

CLINICAL SIGNS

• Signs depend on the degree of trauma and whether urinary obstruction is present.

• Some cats with bladder or renal uroliths may be asymptomatic. However, clinical signs include the following:

Hematuria

Dysuria

Urinating in strange places

Straining to pass urine (owners may report the cat is constipated)

Vomiting

Collapse, death

DIAGNOSIS

• Radiology may show uroliths on routine films.

• If there is a strong suspicion, a double-contrast study should be done.

• Ultrasonography locates the position of uroliths in the urinary tract.

• An analysis of the uroliths is critical for proper treatment.

• Small uroliths may be collected by catheter while obtaining a urine sample.

TREATMENT

Medical treatment

• Struvite uroliths can be treated by inducing their dissolution. By feeding a diet that reduces urine pH to 6 to 6.3 and that is low in magnesium (Prescription Diet Feline S/D), uroliths will dissolve. This type of diet may also prevent the recurrence of these uroliths.

• Dissolution is usually completed in 4 to 8 weeks. Animals should be examined radiographically every 2 to 4 weeks to monitor the dissolution process. Continue the diet for 1 month after all uroliths have disappeared.

• Antibiotic treatment helps prevent secondary bacterial infections that may occur in traumatized tissues.

Surgical treatment

• Consider surgery for uroliths that do not resolve with diet.

• Postsurgical radiographs should be taken to ensure that all uroliths have been removed.

TREATMENT (FOR OBSTRUCTIVE UROLITHS)

Medical treatment

• Uroliths must be retrograded back into the bladder or removed from the urethra. Using a well-lubricated, open-end feline catheter, which has been atraumatically inserted in the urethra (under sterile technique), and a saline or lactated Ringer’s solution, gently propulse the urolith back toward the bladder. This reestablishes urine flow and allows time for further medical management (Fig. 12-6).

• Dietary dissolution: Diets low in magnesium, which promote a urine pH of 6 to 6.3, are recommended for dissolution of struvite uroliths (Prescription Diet Feline S/D). Dissolution may take 4 to 8 weeks. Follow progress with radiographs taken every 2 to 4 weeks. Continue diet for 1 month after uroliths disappear from the radiographs.

• Antibiotics should be used to prevent secondary bacterial infections in the already traumatized urinary tract. Choice may be empirical or based on culture and sensitivity results.

• Monitor the animal’s urine flow daily, because reobstruction may occur.

Figure 12-6 Introducing a urethral catheter into a female cat.

Surgical treatment

• Surgery (perineal urethrostomy with or without cystotomy) should be performed if uroliths cannot be removed from the urethra or dissolution does not occur. Owners should be advised of the risks associated with perineal urethrostomies (increased bladder infections, strictures). A cystotomy may be needed to remove the uroliths in the bladder.

INFORMATION FOR CLIENTS

• If the uroliths do not dissolve, surgery is required.

• Feed the cat the prescription diet exclusively. No treats or table food!

• Medical treatment requires periodic monitoring by radiography and urinalysis.

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