Dog Owner's Home Veterinary Handbook.pdf - Mr. Walnuts

BLADDER AND URETHRAL STONES
THE URINARY SYSTEM • 415
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 recurence.
Surgical removal is the treatment of choice for urethral stones that cause
obstruction (see Obstructed Bladder, page 416) and for bladder stones that fail