Urinary tract infections (UTIs) are common in dogs, often leading to bloody urine (hematuria), difficulty or pain when urinating (dysuria) and frequent urinations (polakiuria). Under the right circumstances, bacterial infection of the canine bladder can also lead to the formation of struvite (triple phosphate) stones.
Struvite Bladder Stones Form in the Presence of Urinary Tract Infection in the Dog
There are several different types of stones which may be found in the canine urinary bladder. Struvite stones are one of the two most common forms of bladder stones diagnosed in the dog.
Struvite stones are formed of a complex of minerals, primarily magnesium, ammonium and phosphate. They were previously referred to as triple phosphate stones and this terminology is still commonly used.
Struvite bladder stones form as a result of a complicated series of reactions which occur in the presence of specific types of bacteria which are able to digest urea, called urease-positive bacteria. Urea results from the normal metabolism of proteins by the canine body and is excreted as a waste product in normal urine. Struvite crystals (which differ from struvite stones) are also found in the urine of normal dogs.
In the presence of urease-positive bacteria, urea is broken down to ammonia which is toxic to the cells in the lining of the bladder. This toxicity causes inflammation in the bladder, also known as cystitis, and results in proteins being released into the urine as part of the inflammatory response. The proteins now present in the urine combine with the struvite crystals to form a matrix which is the foundation for a struvite stone.
The bacteria most commonly involved in the canine urinary tract infections which result in the formation of struvite bladder stones are Staphylococcus and Proteus. Though both male and female dogs can develop struvite bladder stones, the majority are seen in female dogs.
Diagnosing Canine UTI Complicated with Struvite Bladder Stones
In addition to the signs normally encountered with UTIs in dogs, recurrent urinary tract infections are common due to the continuing presence of the stone in the bladder.
Struvite stones require the presence of bacteria to form. Staphylococcus is the most common infecting bacteria, but Proteus is also diagnosed with regularity as a cause of bladder infection in dogs with struvite stones.
Unlike some of the other forms of bladder stones seen in dogs, struvite bladder stones form only in an alkaline urine pH. The alkaline pH of the urine is a direct result of the infection in the bladder. The pH of the urine is easily determined by a urinalysis which can be performed by your veterinarian.
Struvite stones are radio-opaque, which means that they can be visualized on a radiograph readily. In some cases, the stones may even be palpable through the abdominal wall.
Dogs with struvite bladder stones may have one stone or many. The stones can vary in size from small to quite large. When removed from the urinary bladder, they resemble a common pebble or rock which is tan in color.
The definitive diagnosis of the composition of any canine bladder stone is through laboratory analysis of the mineral composition of the stone. Canine bladder stones may be of a mixed composition on occasion, with one layer of the stone being formed of struvite and another being formed of a different mineral content (such as calcium oxalate).
Treatment of Canine Urinary Tract Infections and Bladder Stones
When struvite stones are present in a dog, the infection must be treated with an appropriate antibiotic. Without control of the infection, the stones are likely to return even if they are physically removed.
Treatment of struvite stones can be accomplished by:
- surgical removal
- urohydropropulsion (a means of manipulating the stones in the bladder so that they can be voided)
- dissolution through the use of a specialized diet
Bladder Stones and UTI in Dogs
Dogs which have recurrent urinary tract infections, particularly those which are female, should be evaluated for the presence of bladder stones. Though there are many different types of stones which can form in the canine urinary bladder, struvite stones are one of the most common and always occur in the presence of an infection within the bladder.
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