Current Trends in Urolith Submissions in Canada

Doreen Houston Canada

The Canadian Veterinary Urolith Centre (CVUC), located in Guelph, Ontario, Canada, opened in February 1998. This collaborative effort between Veterinary Medical Diets (VMD) and the University of Guelph has been highly successful with more than 15,000 submissions quantitatively analyzed over the past three years. Approximately 60% of the submissions have been from canines and 40% from felines. Submissions have been received from all parts of Canada, including 25% from Western Canada (British Columbia, Alberta, Saskatchewan, and Manitoba), 47% from Ontario, 18% from Quebec, and 10% from Eastern Canada (Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland).

Dogs

Approximately 47% of submissions were struvite, 39% oxalate. Females outnumbered males approximately 10:1 in struvite stone submissions. Most struvite stones in dogs are infection-induced and female dogs are at greatest risk. This is likely due, at least in part, to the anatomy of the female urethra (short and wide compared to the male). Urea-splitting bacteria, most commonly Staphylococcus, Proteus and Ureaplasma, result in an elevated urinary pH and struvite crystal and stone formation. Medical dissolution of struvite stones in dogs is not as easy as in cats. The high prevalence of infection-induced struvite, the prevalence of fine concentric laminations with low porosity and the relatively common occurrence of apatite in struvite uroliths are reasons why dietary dissolution takes longer in dogs compared to cats. Current dissolution diets for struvite uroliths are high in fats and salt; care must be taken in feeding such diets to dogs with a tendency towards obesity, pancreatitis, hyperlipidemia, or salt-intolerant conditions such as heart and kidney disease.

Males outnumbered females approximately 2.3:1 in canine calcium oxalate stone submissions. This is similar to what is reported in other studies. Many of the dogs with oxalate were older; a number had documented serum hypercalcemia. Unlike the situation with struvite in dogs, infection does not appear to be a contributor to oxalate stone formation. Urinary tract infections can and do occur secondarily to the presence of any type of bladder stone. Although oxalate crystals can form at any urine pH, most dogs had urine pH < 6.5 at the time of urolith diagnosis. As dietary dissolution is not possible for oxalate uroliths, voiding hydropulsion or surgical removal is indicated.

Canine breed and gender composition of urinary calculi from the top six breed submissions are summarized in Table 1 (data based on the first 13,000 submissions to the CVUC). Although mixed breed dogs accounted for the majority (21%) of canine submissions, note the overrepresentation of cases from small purebred dogs (Miniature Schnauzer, Bichon Frise, Shih Tzu, Lhasa Apso, and Yorkshire Terrier). Additionally there is a strong tendency for males in these breeds to form oxalate, the females struvite. The female Schnauzer may be an exception to this tendency, as she appears to have a 50:50 chance of developing an oxalate or a struvite stone. Dalmatians are at highest risk for urate stone development with males 24 times more likely than female Dalmatians to develop urate stones. Dalmatians have a genetic tendency for urate urolithiasis and risk of recurrence is great.

Discussing risk factors for urolith formation with owners of over-represented breeds and monitoring urine may help in early identification, treatment and prevention of uroliths.

Less commonly submitted uroliths included cystine, xanthine, silica and calcium phosphate. Cystinuria is an inborn error of metabolism and its mode of inheritance has been documented in the Newfoundland dog. Xanthine urolithiasis is uncommon and occurs naturally in breeds such as the Cavalier King Charles Spaniel and Dachshund and secondarily in dogs receiving allopurinol (a xanthine-oxidase inhibitor, used in the management of ammonium urate urolithiasis). Silica uroliths may occur in dogs with a pica for eating soil or in dogs eating diets high in cereal grains containing silicates such as corn gluten and soybean hulls. Calcium phosphate uroliths occur in the same breeds as calcium oxalate uroliths and risk factors are similar. Calcium phosphate crystals are commonly found as a minor component with struvite uroliths.

TABLE 1: Stone composition and sex of top six canine breed submissions.

Cats

The majority of stones/urethral plugs came from domestic short hair and domestic longhair cats (82 %), Himalayan (5.5 %), Persian (3.5 %) and Siamese (2.1 %) cats. Approximately 53 % of submissions were struvite, 39 % oxalate. The majority of cats with struvite uroliths were domestic short hair and domestic longhair cats. A significant number of these cats were overweight. Males outnumbered females 1.4:1 in struvite submissions (about 25% of the struvite submissions in male cats were urethral plugs). Unlike the situation in dogs, many of the struvite plugs and uroliths in cats are sterile. Most of the submissions obtained came from cats with high urine specific gravities (often > 1.045) and urine pH in excess of 6.4.� The majority of cats with oxalate urolithiasis were older (more than five years). Males outnumbered females 1.5:1 in oxalate submissions. Male Himalayan, Persian and Siamese cats appeared to be at greater risk of developing oxalate uroliths compared to struvite uroliths. Again, many of the submissions obtained came from cats with high urine specific gravities.� Less commonly submitted uroliths included ammonium urate, cystine, xanthine, silica and calcium phosphate.

Current recommendations for cats with a history of lower urinary tract disease include:

Modifying the cat�s environment by:

 Identifying and decreasing stress.

 Providing at least one litter box/cat in the household.

 Avoiding covered litterboxes.

 Using unscented, fine-grained type litters.

 Changing the litter frequently.

 Providing the cat with toys and scratch posts that allow the natural �hunting� behavior to be manifested.

Increasing water consumption by:

 Feeding increased amounts of canned food.

 Providing easy access to fresh water at all times.

 Using a bowl with a wide surface area and keeping the water bowl full at all times (cats have very sensitive whiskers and many seem to prefer a large bowl in which the whiskers do not touch the sides of the bowl).

 Trying a variety of water types (Brita, distilled, bottled, warm tap water, cold tap water).

 Providing a source of running water (water fountains are available for cats).

 Feeding ice cubes flavored by tuna or clam juice.

 Keeping food and water bowls away from the litter box area.

 Keeping the water bowl clean (cats have a very keen sense of smell and are easily turned off by odors on the edge of the bowl).

 Changing the nature of the water bowl (some cats prefer a clear glass bowl).

Current recommendations for dogs and cats at risk of repeat urolith development include:

1. Examination of urine pH, specific gravity and sediment at two weeks, four weeks and then every three months post urolith removal or dissolution. This follow-up helps determine if the owner is being compliant with your recommendations (diet, water intake, etc.) and allows for modification of diet as necessary. Please note that it is very important to determine pH as soon as urine is collected. Urine pH will rise as the urine is allowed to sit, especially if cooled. Urine pH will also rise in a stressed cat.

2. Please note: urine pH is usually most acidic in the fasted animal. Urine pH rises two to six hours following a meal.

3. Radiographs (plain, contrast) or ultrasound examination every two to four months in high-risk breeds and in dogs diagnosed with metabolic uroliths (e.g., urate, cystine). Uroliths detected when small may be removed by voiding hydropulsion. It is important to note that some stones (urate, cystine) are often radiolucent necessitating contrast or ultrasound examination.

4. Increased water consumption (canned food, soaked kibble, flavoured water) See above recommendations for cats.

Kidney and ureteral stones

Kidney and ureteral stones accounted for approximately 1% of all submissions to the CVUC. Many kidney and ureteral stones are not removed and are thus not submitted for analysis. Most of the dogs and cats that develop renal stones are mid-age to older. As previously reported, the overwhelming majority of kidney stones in cats are oxalate in nature, with males outnumbering females. In dogs, oxalate and struvite stones were submitted with oxalate outnumbering struvite submissions. Female dogs were at highest risk for struvite nephroliths. Oxalate nephroliths were found in greatest numbers in dogs older than six years of age (males outnumbered females 1.5:1). Similar to bladder uroliths, renal uroliths appeared most often in Miniature Schnauzers, Shi Tzus, Lhasa Apsos, Yorkshire Terriers and Bichon Frise dogs.

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