There are multiple urinary issues that can occur in cats and dogs and we've covered a few of them in past espisodes of A Vet's View. You can find those topics at the links below:
This week and next week we are going to discuss canine urinary stones. While dogs and cats can certainly get stones in their kidneys they more frequently get them in their bladders. This is ultimately the better location as it is far easier to retrieve stones from a bladder than it is from the kidneys. There are several different types of stones that dogs and cats can from in the bladder and today we will discuss struvite stones. Next week's topic will be oxalate stones.
Dogs and cats with urinary stones may present with similar signs as pets with urinary tract infections, cystitis or even bladder tumors. They may also present with no clinical signs at all. While different stones are going to b approached using different measures the initial work up for a pet with urinary issues is typically the same. A urinalysis with either ultrasound or x rays (I prefer ultrasound) combined with a urine culture is the basic minimum data base or starting point. If we identify stones using either ultrasound or x ray we will use the urine pH from the analysis to give us an idea of the type of stone. This is only an idea, however, as it is possible for stone populations to be mixed and there are more than two types of stone.
Struvite stones occur in an alkaline or basic (pH is more than 7.0) urine and are typically associated with infections. There is a specific line of English Cocker Spaniels that have a genetic predisposition to forming struvite stones without the presence of infection but for our purposes it is safe to say that struvite stones equal infection. Struvite crystals in urine are relatively normal, they form when magnesium and ammonium bind to a phosphate ion. This is typically of no consequence but when bacteria that can digest urea are present in the urine they produce ammonia, ammonia is a very irritating substance. When ammonia produces inflammation in the bladder, inflammatory proteins are released into the urine. These proteins form a matrix that allows the struvite crystals to come together to make stones. It is not unusual for the bacteria that are digesting the urea to become encrusted in these stones which leads into the various treatment plans and why I would really only consider there to be two plans.
Treating struvite stones should be based on at least a reasonable assumption that the stones are struvite. Without having a stone in hand to submit to the laboratory we are left relying on the ultrasound (or x rays), a urinalysis and the urine culture. If the stones appear to be small enough to be retrieved with a cystoscope then that is a perfectly reasonable avenue and requires referral to a facility that has a scope small enough to fit your dog's urethra and someone well trained in retrieving stones with the scope. The other option would be surgical removal of the stones. In either case the stones should be submitted to a laboratory for analysis. It is possible that another type of stone created the inflammation and then the proteins involved in the inflammation simply added to the preexisting stones using struvite crystals.
While it is possible to dissolve the stones using diet, I am not a huge advocate of this method nor do I consider it to be a reasonable alternative when we are comparing it to surgery in most cases. My reasoning has to do with the length of time and the amount of monitoring involved if we are going to do it correctly. When we opt for less invasive measures it is almost always a financial reason. Occasionally there are medical reasons to not go for surgery and sometimes people have personal belief systems that make surgery less desirable for their pets and in those cases I am on board with dietary dissolving of stones. For the money it's just not a cheaper alternative if you are going to do it properly and if you are not going to do it properly you aren't going to do it with me. To dissolve with diet we have to use a diet that changes the pH of the urine; these are commercially available. We also will want to keep your pet on antibiotics for the entire duration of the treatment as the bacteria that are causing the problem can become encrusted in the stones. Fluffy or Cuddles will have to return at least monthly to have the bladder stones remeasured using ultrasound or x ray. The typical course of treatment is around four months. If we do that math out, dietary dissolving of stones will cost well over $600 by 2012 prices and may not work. It may also create stones that gradually become smaller but then become entrapped in the dog's urethra and need to be removed surgically in an animal that is seriously compromised. I would just bite the bullet, have the surgery, and be done with it if it were up to me.
After treatment the antibiotics will be continued until the urine culture is negative. After that regular checkups including ultrasound (or x rays) of the bladder and urine cultures will be necessary to prevent future infections from occurring and possibly forming more stones. Dietary changes are not only unnecessary but may lead us into a sense of false security. We may get the impression that we are actively preventing stones and may not need to be as proactive about monitoring and this could lead us into trouble. That is unless your dog is an English Cocker Spaniel, then I would suggest a dietary change.
Next week we'll read about Oxalate Stones.