Bladder and Urethral Stones in Dogs
Kidney stones are rare in dogs. Bladder stones 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 (that is, they're 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. There is a genetic test offered by VetGen, OptiGen, and PennGen to detect carriers and affected dogs with this problem. Silica stones are rare; they occur most often in male German Shepherd Dogs. These stones are not usually associated with a preexisting 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.
Treatment: Bladder infection, if present, is treated as described for Cystitis (page 414). 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-accomplished by feeding Hill's Prescription Diet s/d, or Royal Canin Urinary SO 13. Uric acid stones respond to a low-purine diet (Hill's u/d), along with the drug allopurinol. Cystine stones also respond to Hill's u/d, along with drugs that dissolve cystine. Feeding a vegetarian diet, such as Royal Canin Vegetarian Formula, may help prevent urate stones. 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 percent 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.
A stone is the most common cause of an obstructed bladder. Tumors and strictures are less common causes. Enlargement of the prostate gland is a rare cause of bladder obstruction in male dogs.
A dog with an obstructed bladder is acutely uncomfortable or in dire distress. Males and females often assume a peculiar splay-legged stance while attempting to void. A partial blockage can be suspected when the dog dribbles urine, voids frequently, and has a weak, splattery stream.
A partial obstruction, left untreated, may become a complete obstruction. With a complete obstruction no urine is passed. The lower abdomen becomes swollen and tender to pressure, and it feels as if there is a large ball in front of the pelvis. Note that the continuous straining associated with an obstructed bladder can be mistaken for constipation.
Treatment:Adog with a partial obstruction due to a urethral stone may pass the stone spontaneously. Treatment thereafter is similar to that described for Bladder and Urethral Stones, page 415.
A complete obstruction is an acute emergency. Take your dog at once to the veterinarian. If the blockage is not relieved, the dog will go into kidney failure or the bladder could rupture. Often the stone can be pushed back into the bladder using a sterile catheter, or by infusing water under pressure into the urethra. If not, surgical removal will be necessary.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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