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Dogs, cats, and humans alike can suffer from urinary stones, or uroliths, a dreaded buildup of irritating substances in the urinary tract that causes pain and even obstruction. There are several kinds of stones, some of which occur more commonly in certain breeeds. Symptoms of urolithiasis include bloody urine, frequent urination, painful urination, and straining. If the stones move into the urethra (the tube that transports urine from the bladder to the outside), they can obstruct the flow of urine. For some types of stones and crystals, nonsurgical therapies — diet changes, nutritional supplements, drugs — may be all the treatment needed. The treatment for stones that cause obstruction is almost always surgical.
In some dogs and cats, crystals can form in the urine, causing irritation, infection, pain, and/or obstruction anywhere along the urinary tract (from the kidneys to the tip of the urethra). The crystals can in some cases coalesce into stones called urinary calculi or uroliths, hence the name of the resulting disease: urolithiasis.
In both dogs and cats, these uroliths most commonly cause a problem when they dwell in the bladder, causing irritation, inflammation, and infection, and/or when they pass through the urethra, where they can cause all of the above as well as complete urinary obstruction.
Complete obstruction of urine flow is an immediately life-threatening problem, because urine backs up in the urinary tract, causing toxins to build in the bloodstream. If the flow is not re-established, accumulation of these toxins leads to deadly heart rhythms and other potentially irreversible toxic changes to the body veterinarians ascribe to the effects of acute kidney failure.
Any dog or cat can experience urinary stones, but some breeds of dogs are predisposed to form certain kinds of stones. Many Dalmatians, for example, cannot metabolize uric acid in their livers properly, leading to an excess of uric acid in the urine. Because uric acid is not very water soluble, it can form urate crystals, which may then coalesce into stones. Urate stones can also form in pets with certain liver conditions.
For some other breeds, a defect of another metabolic pathway leads to excess quantities of the amino acid cystine. Cystine can crystalize in the urine and lead to stone formation within the urinary tract. This latter version of urolithiasis is called cystinuria, and may occur more often in Newfoundlands and Siamese cats.
Struvite (aka, triple-phosphate) uroliths and calcium oxalate uroliths are other types of urinary stones that are very common in many breeds of dogs and cats. Certain diets, mineral supplements or metabolic problems may lead to an excess of a substance in the urine, which may lead to the development of these stones.
Signs of urolithiasis are usually related to inflammation or infection in the urinary tract. Bloody urine, frequent urination, painful urination, and straining are common signs.
For dogs and cats whose stones pass into the urethra, urinary obstruction becomes a distinct possibility. In cases where urine flow is completely obstructed, most signs are associated with the resulting acute kidney failure. Sudden onset of vomiting, anorexia, and lethargy is most typical of these cases. Due to the small aperture of the penile urethra, males are over-represented among patients who suffer complete obstruction. Owners who notice pets straining to urinate, with no success, should recognize that this is a medical emergency, and pets should be seen by a veterinarian immediately.
Diagnosis can usually be made with X-rays or ultrasound. Alternatively, contrast urography (with air or dye) is a great way to demonstrate the presence of stones that don’t show up on normal X-rays (as is often the case with urate uroliths). Urinalysis and urine culture and sensitivity are a critical part of this process. Definitive diagnosis, however, can be achieved only once stones are retrieved and analyzed for their chemical makeup.
The treatment for uroliths that cause obstruction is almost always surgical. A cystotomy is the most common urolith surgery, and requires an incision in the abdomen and urinary bladder for stone removal. When urethral obstruction occurs, however, surgeons may be forced to perform a urethrotomy, or an incision into the urethra, to retrieve the stones and re-establish normal urine flow.
Though less frequently performed, the nonsurgical use of lasers or ultrasound waves to break down stones so they might pass is also a possibility for pets, when owners have access to highly specialized facilities.
For some types of uroliths and crystals, nonsurgical therapies may be undertaken. Diet changes, nutritional supplements and drugs can sometimes be implemented to help dissolve stones, particularly in the case of struvites and urates.
In many cases, treating secondary urinary infections with antibiotics may be part of treatment protocol.
Though the traits that allow for certain kinds of stone formation are preventable only through judicious breeding, other types of stone formation can often be prevented through nutritional management.
This article has been reviewed by a Veterinarian.
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