The first thing you probably think of when we say “kidney stone” is “pain.” Kidney stones can certainly be painful for some dogs, but did you know that other dogs may not have any symptoms? There’s some interesting science behind kidney stones and how they’re formed — let’s learn more.
They Start as Crystals
Urine is mostly water (about 95 percent), but it also contains substances that can play a role in the formation of urinary crystals and stones. The crystals are microscopic, but the stones are larger rock-like clumps that are often visible without a microscope. The presence of crystals in urine doesn’t automatically lead to stone formation, but they do represent a risk of the dog developing stones. Urinary stones are called kidney or bladder stones depending on their location, and kidney stones are also called nephroliths (“nephro-” meaning kidney and “-lith” meaning stone).
Types of Stones
Kidney stones can be formed from several different minerals, including magnesium, ammonium, phosphate and calcium. They can also be formed from oxalate, which is a naturally occurring compound found in food. Calcium oxalate is the most common type of kidney stone in dogs, accounting for more than 70 percent of them. Struvite, which is made up of magnesium, ammonium and phosphate, is another type of kidney stone that dogs may have issues with. There are several other types of stones dogs can develop, but they are not common.
The Formation of a Stone
Struvite stones are typically associated with a bacterial urinary tract infection (UTI). This makes treatment of the infection essential to resolving stone formation. The exact cause of calcium oxalate stone formation isn’t fully understood. Some breeds are more predisposed to stone development than others (schnauzers, shih tzus, Yorkshire terriers). Many factors such as urine pH, hydration status, diet and metabolic issues can play a role in the formation of calcium oxalate crystals.
Detecting a Kidney Stone
Many times, dogs with kidney stones do not have any outward signs. Stones are often detected when undergoing X-rays for unrelated reasons. If symptoms are present, they are usually due to a concurrent kidney infection or another kidney disease. Signs related to kidney stones may include blood-tinged urine, abdominal and/or back pain, vomiting and anorexia.
If symptoms, a physical exam and urinalysis indicate a potential urinary issue, your veterinarian may perform an abdominal X-ray or ultrasound to confirm the presence and location of urinary stones. Bladder stones are much more common than kidney stones. By examining a urine sample, the type of crystals present in the urine can help to determine the type of stone. This information is used by your veterinarian to make an appropriate treatment plan.
A Range of Treatment Options
If the kidney stones are not currently causing problems, intervention may not be needed and your veterinarian may recommend regular monitoring for changes. If action is required, the type of stone will determine the treatment options.
Some stones, such as struvite, can be treated with medical therapy including a therapeutic diet and appropriate administration of antibiotics. Therapeutic diets are usually low in magnesium and phosphorus. Unfortunately, calcium oxalate stones can’t be dissolved by changing your dog’s diet.
Another option for removal of kidney stones is extracorporeal shock wave lithotripsy (ESWL). This procedure uses shock waves to break up the stone into smaller pieces that can pass through the urinary tract. This procedure is minimally invasive and usually successful but may not be readily available. Additionally, some specialists can remove stones via percutaneous nephrolithotomy or surgically assisted endoscopic nephrolithotomy.
Surgery to remove kidney stones is much more complicated than surgery to remove bladder stones. In some cases, it may be possible to surgically remove the stone from the kidney; however, sometimes the entire kidney may need to be removed.
Kidney stones can cause pain and result in serious illness, including blocking the urinary tract — potentially a life-threatening situation. If you think your dog is showing signs of a kidney stone, have them checked by your veterinarian.
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