Like a Rolling Stone

April 14, 2013

Bichon_FriseOh boy, did I get to perform a fun surgery this week! My favorite surgery to perform is a cystotomy, where an incision is made into the bladder to remove uroliths (bladder stones). While kidney stones are common in humans, they are uncommon in cats and dogs. Bladder stones, however, are a frequent finding in our canine and feline companions.

There are several different types of stones that can form in cats and dogs. Far and away, the most common urinary tract stones are either calcium oxalate or magnesium ammonium phosphate (commonly calledstruvite). In dogs, struvite stones occur most commonly as a complication of abacterial urinary tract infection certain types of bacteria can change the pH of the urine in the bladder, and result in struvite stone formation. Cats rarely develop bacterial urinary tract infections, but they do form struvite stones. It’s not well understood why some cats develop these stones. Calcium oxalate stones can form in certain breeds that are predisposed to this problem, or if the animal’s blood calcium levels are too high for some reason (hypercalcemia.) There are two types of treatment for struvite stones: dissolution via prescription diet therapy or surgical excision via cystotomy.

Cat in litter panWhy wouldn’t we always recommend dissolution over surgery, since this is obviously less invasive and much less expensive than surgery? Unfortunately, we cannot know what stone type is present in the bladder without obtaining a stone and submitting it to our lab for chemical analysis. Struvite stones are present only about 40% of the time. Thus, it’s a dice roll as to whether the stones can be dissolved or not. It can take several months to dissolve stones, and during that time Fluffy or Fido may be experiencing significant bladder pain, passing bloody urine and possibly urinating in the house. Once urinary tract stones have been identified as a problem, male cats and male dogs are at risk for developing a urinary tract obstruction, where a small fragment of bladder stone blocks the urethra, preventing the animal from urinating. This is a life-threatening emergency when it occurs, and requires immediate medical intervention. (Fortunately, this problem rarely occurs in female dogs and cats, since females have a much shorter, and wider urethra.)

Penny's radiographMore often than not, when we identify uroliths, our recommendation is for surgical excision of the stones. And that’s just what I got to do this week, when I took “Penny”, an 8 year old female Bichon Frise to surgery. Penny had presented to one of my colleagues for straining to urinate, urinating in the house and passing visibly bloody urine. My colleague, upon feeling Penny’s bladder, could palpate a large number of stones. Penny then had an abdominal radiograph (x-ray) to visualize her bladder. Penny’s radiograph is pictured here to the left. This is a lateral view of Penny, where she is laying on her side with her head to the left of the picture and her tail to the right. In the bottom right-hand corner of the radiograph you can see a large number of round, white structures; these are Penny’s uroliths…there are too many to count!

Penny's urolithsI was able to surgically remove over 50 stones from Penny’s bladder, ranging in size from pinpoint to the size of grapes (shown in this photo, left). The stones were submitted to our lab for analysis, and they were determined to be calcium oxalate. Certain breeds of dogs (Bichons being the most common) are predisposed to calcium oxalate stone formation; this is a frustrating problem for all parties involved since the stones have a high likelihood of returning after surgery. (I heard an internal medicine expert say once that Bichons start forming new stones the minute after their stones are surgically excised!)

What can be done to prevent stones from returning? We have much better success at preventing struvite stones than calcium oxalate stones. In virtually every patient where uroliths have been a problem, we recommend a prescription diet. Prescription urinary tract diets are able to create a neutral urine pH, have a reduced calcium, magnesium, oxalate and phosphorous content, and often contain higher sodium (salt) levels, which causes the pet to drink more. Increased fluid intake, either by drinking more, or eating a canned food diet, is also a mainstay of therapy to dilute out the urine. The less concentrated the urine is, the less likely it will supersaturate with the minerals needed to precipitate stones. Finally, in dogs prone to calcium oxalate stones, we may prescribe a medication known as potassium citrate; this medication increases the pH of the urine. Since calcium oxalate stones require an acidic pH to form, by making the urine pH more alkaline, we can decrease the incidence of stone formation.

CrananidinFor dogs prone to urinary tract infections, we often recommend cranberry supplements. (This concept may be familiar to women who have suffered from a UTI.) Cranberry has been shown to inhibit the binding of E. coli and other bacteria to the bladder wall, thereby preventing infection. Frequent voiding, ample access to fresh water, and adding water to the food are also recommended for these patients.

Uroliths are something we diagnose on an almost weekly basis; clearly this is a very common problem in cats and dogs. If your pet is straining to urinate, producing bloody urine or seems to have a urinary tract infection that doesn’t resolve with antibiotic therapy, it may be indicated to rule out bladder stones. Fortunately, Penny recovered well from her surgery. Now, we need to monitor her urine every 3 months to ensure her pH is appropriate, and that she’s creating urine dilute enough to minimize stone formation. She will require a lot of close monitoring for the rest of her life, but hopefully we will successfully prevent those stones from returning!

 

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