Bladder stones in pets: what to watch for and how we treat them

Bladder stones can be just as much of a painful problem for dogs and cats as they can be for humans. A recent case Dr. Kyle Fuller treated here at Cascade Hospital for Animals showed just how big of a problem bladder stones can grow to be and how critical it is to treat them on time.

An x-ray shows shows Rosey's bladder filled with stones.Rosey is a Japanese Chin whose bladder stone case appeared for an usual reason. “Most of the time, we diagnose bladder stones because people bring in their dogs for straining to urinate, blood in the urine, or having urinary accidents in the house,” said Dr. Fuller. “But in Rosey’s case, she had no urinary symptoms. We caught the bladder stones in an x-ray of her leg we took because she was limping. She had no clinical symptoms at home.”

It turned out that poor Rosey had two unrelated but serious issues: many bladder stones, some of them quite large, and a torn cruciate ligament. Due to the size of the stones, Dr. Fuller performed surgery to remove them. “She wasn’t showing symptoms yet, but she would be soon,” Dr. Fuller said. “Her stones were so large that I was worried it was going to take too long to try to dissolve them. She had probably about 200 stones in her bladder.”

Two possible culprits

Cats and dogs can get one of two types of bladder stones: oxalate and struvite. Even for experienced vets like Dr. Fuller, it’s next to impossible to definitively tell the difference between the two types. ”The only way to tell the difference is to send the stones out to the lab at the University of Minnesota,” Dr. Fuller said. “And the only way we usually get the stone is through surgery. Unlike with humans, it’s rare for them to pass stones and for us to be able to retrieve the stone.”

The type of stone usually determines the reason the stone formed and the course of treatment that will follow. Struvite stones most often form as a result of an untreated silent urinary tract infection  “They’re caused by urease-producing bacteria that feeds on substances in the urine and creates the underlying material that forms the stone,” said Dr. Fuller. “So it’s really important in dogs that have struvite stones, after they’ve been diagnosed and treated, that they have regular follow-up appointments to check and make sure they’re not developing another urinary tract infection.” 

It’s all in the dietDr. Fuller poses with a healthy puppy during a wellness check.

Ordinarily, struvite stones are treated with diet. “If we know that they're struvite stones, we try to get them to dissolve with diet, and that works better for stones that are smaller and it works better when they don't have as many stones,” said Dr. Fuller.  Although she learned after the fact that Rosey’s bladder stones were struvite, in her case, surgery was still the best option..

Oxalate stones tend to form due to a genetic predisposition to form them. Dogs with conditions such as Cushings disease or hypercalcemia, which is elevated blood calcium, for example, can develop oxalate stones. “It’s not as easy to prevent oxalate stones as it is to prevent struvite stones. So we also want to check regular x-rays of the bladder for dogs with oxalate stones,” she added. 

“And just as struvite stones are formed because of bacterial infections, the stones themselves, whether they're struvite or oxalate, can also predispose dogs to getting bacterial urinary tract infections because the surface of the stone provides a place for bacteria to grow and sort of hide from the body's normal immune defenses. A lot of the stones have little irregular pockets on the surface that the bacteria will hide in. So with both types of stones, we want to regularly check for urinary infections.”

Dr. Fuller and other veterinarians recommend prescription diets for dogs and cats with a history of both types of stones. “They help promote dilution of the urine, so the urine is less concentrated, which decreases the likelihood that a stone will form. The diet is lower in minerals like calcium that contribute to stone formation and it promotes a pH that is less likely to lead to stone formation. And it also has supplements in it like omega fatty acids, antioxidants, and potassium citrate, all of which decrease the likelihood of stone formation.”

Avoiding an emergency

Left untreated, bladder stones can quickly go from an inconvenience to a potentially deadly emergency, which is why in cases like Rosey’s, veterinarians need to act quickly.

“For Rosey, the stones had already grown so large that they were stretching her bladder, and at some point she would've started showing pain with urination or blood in the urine,” Dr. Fuller said. “It's also possible for one of those stones to try to pass and get stuck in the urethra on the way out and that's considered a surgical emergency. What we usually do is flush the stone that's stuck in the urethra back up into the bladder, and then we do surgery on the bladder to remove all the stones.”

It can be life-threatening to have a large, obstructive stone in the bladder. “Because when the bladder is not able to empty itself of urine, it sends signals to the kidneys to stop producing urine, leading to kidney failure. Also if the bladder ruptures, then there's a bunch of urine in the abdomen and that's also bad because urine is very irritating.”

In Rosey’s case, her bladder stone surgery went well, and she’s being carefully monitored to see if she needs surgery on her cruciate ligament, something smaller dogs can sometimes stabilize on their own. “She’ll need monitoring and x-rays on her bladder to watch for signs of infections, but so far she’s doing great recovering at home,” said Dr. Fuller.