Bladder and Urethral Stones
Kidney stones are rare in dogs. Bladder stones however, are common. Stones that form in the bladder may pass into the urethra. All dogs can develop bladder stones. Breeds with an increased incidence include the Miniature Schnauzer, Dalmatian, Shih Tzu, Dachshund, and Bulldog.
Bladder and urethral stones may be large or small, single or multiple, and may pass spontaneously or obstruct the lower urinary tract. Stones in the bladder eventually cause painful urination and blood in the urine.
Most bladder stones are struvites (meaning they are composed of magnesium ammonium phosphate). They form in an alkaline urine and are usually preceded by a bladder infection. The bacteria and urinary sediment form a nidus around which the ammonium phosphate is deposited.
Uric acid stones form in an acid urine, and are frequently associated with inherited alterations in urate metabolism. Dalmatians and Bulldogs are genetically predisposed.
Other stones are calcium oxalate and cystine stones. Cystine crystals have been found in Newfoundlands and many other breeds.
Silica stones are rare - they occur most often in male German Shepherds. These stones are not usually associated with a pre-existing bladder infection.
Stones that are large or numerous can sometimes be palpated through the abdomen. In most cases, the diagnosis is made by X-ray. A contrast dye study may be needed for definitive diagnosis. Stones not visible on an abdominal X-ray can often be seen by ultrasonography or IVP. A urinalysis is routinely obtained.
Stones that pass spontaneously and those that are removed surgically should be analyzed (if possible) since the composition of the stone influences the treatment of any remaining and future stones.
Bladder infection (if present) is treated as described for Cystitis. In many cases the stones can be dissolved over weeks or months by feeding the dog a special diet.
Struvite stones dissolve in an acid urine, requiring a diet low in magnesium and protein. Uric acid stones respond to a low-purine diet, along with the drug allopurinol. Cystine stones respond to drugs that dissolve cystine. Feeding a vegetarian diet may help prevent urate stones, but this may also bring about nutritional deficiencies that will lead to other health problems. There are no methods currently available for dissolving calcium oxalate and silica stones, however, diets and supplements can be used to reduce the risk of recurrence.
Surgical removal is the treatment of choice for urethral stones that cause obstruction and for bladder stones that fail to respond to a diet change and medication. Surgery is also indicated when medical treatment is contraindicated because of congestive heart failure, or when there is a need for more rapid resolution of symptoms.
The formation of new stones occurs in up to 30% of cases. The dog should be seen and checked at regular intervals. Your veterinarian may recommend long-term dietary changes and/or the addition of supplements such as vitamin C, raspberry seed extracts, or cranberry extracts.
There is a genetic test offered by VetGen, OptiGen, and PennGen to detect carriers and affected dogs with this problem.
Please contact your veterinarian with questions regarding this condition.
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