For years, Jody P. Lulich, DVM, Ph.D., Dipl. ACVIM, and his colleagues at the Minnesota Urolith Center have strongly advocated for non-invasive dissolution of uroliths in cats.
Struvite is the most common urolith in cats, accounting for about 46 percent of feline urinary stones, according to data from the Minnesota Urolith Center. And for struvite uroliths, non-invasive nutritional management is the most effective treatment, Dr. Lulich says.
Dietary dissolution is more compassionate and carries less risk, Lulich notes. For the owner, it’s less stressful than seeing her beloved companion undergo general anesthesia, and much less costly. Surgical or laser removal of uroliths can cost upward of $2,000.
Newer research suggests that not only can nutritional management work more quickly than was previously established, but that even a food designed for long-term maintenance of urinary tract health can dissolve struvite uroliths, too, says S. Dru Forrester, DVM, MS, Dipl. ACVIM. Forrester is a scientific affairs representative at Hill’s Pet Nutrition of Topeka, Kan.
Hill’s special dietary formulas, even dry versions, can dissolve struvite stones in as little as two weeks in some cats, Forrester says, eliminating the expense, pain and stress of surgical options.
“It’s exciting news, because we always want veterinarians to think dietary therapy, not surgery, when it comes to struvite,” Forrester says. “Most cats’ clinical signs disappear very quickly with nutritional management, often within a few days. It makes no sense to subject a cat to surgery when you can dissolve uroliths in as little as 14 days.
“There is sometimes a rush to surgery to remove struvite uroliths, but if we can avoid the pain of abodominal surgery, that’s a good thing.”
Controlling pH Is Key
Struvite forms in alkaline urine, typically greater than a pH of 7.5. A therapeutic pet food regimen works by dissolving stones, then maintaining an appropriate urine pH and controlling excessive amounts of minerals such as magnesium and phosphorus, which may lead to urolith formation in the first place, Forrester says.
Typically, Hill’s has recommended that veterinarians prescribe Prescription Diet s/d Feline Dissolution Bladder Health to dissolve stones, Forrester says. They then recommend that clients follow up with Prescription Diet c/d Multicare Feline Bladder Health, which has been designed as a long-term maintenance food to decrease stone recurrence in cats with a known proclivity for struvite disease.
Lulich was lead author on a double-blind clinical trial of the two Hill’s therapeutic pet foods. In the study, which will be presented at the American College of Veterinary Internal Medicine Forum in Denver in June, both Hill’s formulas successfully dissolved struvite uroliths.
Interestingly, complete dissolution took only slightly longer when the maintenance diet was fed—about four weeks on average (utilizing in vivo, a prospective, double-blinded, controlled study using cats with naturally occurring struvite uroliths). That compared to less than two weeks on average when the dissolution formula was fed.
Earlier studies had pegged stone dissolution time at about four weeks for the dissolution formula; the maintenance formula had not been clinically tested, Forrester says. Additionally, the newest study was done using dry food. That’s important, because many pet owners prefer dry formulas to wet food for its convenience.
Such evidence is helpful when it comes to encouraging veterinarians to embrace non-invasive procedures, Lulich says.
Some veterinarians may prefer surgical removal because this is the conventional therapy to remove any type of urolith. But with minimal practice most veterinarians can accurately predict urolith composition using a survey radiograph and supporting information from the urinalysis, Lulich says.
“We also need to dispel the myth that urethral obstruction is likely, as urolith size diminishes using non-invasive dietary dissolution.” Lulich says. “Although possible, urethral obstruction rarely occurs.”
Surgery May Be Needed
Surgery is still the best option in certain cases, says Marianne Diez, DVM, a faculty member at the University of Liège in Belgium.
These include cases involving oxalate or mixed stones; numerous or very large stones; or cats that are unable to eat a moderately acidifying pet food, such as cats suffering from kidney disease. The veterinarian also must be able to ascertain that the client will strictly follow the feeding guidelines and return the cat for follow-up consultations, she adds.
In many cases, however, education and exposure to the benefits of nutritional management are all that’s needed to encourage veterinarians to adopt this method.
For instance, a few years ago, Tamara Padgelek, DVM, owner of a Banfield, The Pet Hospital, in Monroeville, Pa., was treating a female cat suffering from recurring urinary issues. Finally, after radiographs revealed uroliths, Dr. Padgelek was prepared to resort to surgical removal.
But before Padgelek could schedule the procedure, she happened to attend a lecture by Forrester that discussed the topic of nutritional dissolution.
So, upon returning to her practice, Padgelek suggested the dietary therapy to her client. The cat’s stones dissolved within weeks, and Padgelek has since changed her clinical procedures. For most feline bladder stones, she now begins by suggesting nutritional management.
“Clients love it because it’s a less expensive option, and obviously it’s better for the pet if we don’t have to perform surgery,” Padgelek says.
She combines the dietary therapy with pain medication to minimize associated pain during the first week or so of treatment, and antibiotics to treat an infection, if present—all equaling good results for both pet and owner.
It’s the kind of success story Forrester likes to hear.
She points out that in addition to its expenses and risks, surgery is not 100 percent effective. A preliminary study at the University of Minnesota revealed that about 20 percent of cats who have cystotomy performed for urolith removal still have a few stones left after surgery.
“Those stones have a tendency to hide in crevices, so even if you pass a catheter and flush them out, you can still miss a few,” she says. “And on top of that, it’s only going to manage the current uroliths; it’s not going to treat the underlying issue that led to stone formation.”
In most cases, cats still need a special pet food to decrease the risk of forming additional uroliths until they are 8 years old, she says.
This Education Series was underwritten by Hill’s Pet Nutrition of Topeka, Kan.