Dog and cat sharing pet bed
Photo courtesy of Dr. Teri Ann Oursler
Bladder stones, also known as urolithiasis or cystolithiasis, are solid mineral deposits that form inside the bladder of dogs and cats. Stones start out as crystals that form in the urine. These crystals form when a combination of events takes place, such as urine pH change, increased urine concentration, and changes in the mineral makeup of the urine being formed. Over time, the crystals combine and layer together to form bladder stones.
Bladder stones can range from one to two stones to hundreds. Some bladder stones are small and grit-like, whereas others are can grow to be larger than 2 inches in diameter. Bladder stones are quite common in dogs and cats. Kidney stones, more common in humans, occur much less frequently in dogs and cats. Only 2% of stones found in the urinary tract of our pets are found in the kidney.
The two most common types of bladder stones are those made of calcium oxalate and those made of struvite (also known as magnesium ammonium phosphate). Urate is another mineral type that can form bladder stones, but is rare.
Types of Bladder Stones
Struvite bladder stones can occur with bladder infections. Certain bacteria will change the urine’s pH to grow and replicate better. This pH change causes the urine to be more alkaline, promoting struvite crystals to form. Struvite stones can also form without an infection, which is seen more commonly in cats than dogs.
Less is known about why struvite stones form without an infection. They often play a role in idiopathic cystitis in cats (also known as feline lower urinary tract disease), a condition associated with stress and straining to urinate. Calcium oxalate stones tend to form with a more acidic pH, and are rarely caused by bacteria. Other types of stones can occur with toxins (such as antifreeze poisoning) or can be breed-related as occurs in Dalmatians.
Symptoms of bladder stones include straining to urinate, urinating small amounts more frequently, dribbling urine, urinating in unusual places such as inside the house if house-trained or outside the litter box, vocalizing or crying when urinating, and frequently licking the vulva or penis. The urine may have a strong odor and may have mucus or blood in it.
To diagnose bladder stones, a veterinarian will perform a thorough physical examination. Sometimes large stones can be felt by the veterinarian when assessing for internal organ structures of the abdomen called abdominal palpation. Urine can be obtained to look for crystals, pH changes, and evidence of infection. X-rays are almost always necessary to confirm bladder stones. Unfortunately, some stones do not show up well on x-rays, so the veterinarian will need to take into account the symptoms, physical exam, and urine findings.
Determining the type of mineral in the stone is difficult when looking at its shape or appearance. Urine pH can provide clues, but this is also not very accurate. To determine the stone’s composition, it has to be sent to a special laboratory, which can take several weeks for results.
For the most part, surgery is necessary to remove bladder stones. This type of surgery is called a cystotomy. A veterinarian will need to surgically open the abdomen and bladder and pull out the stones. Stitches or staples are used to close surgical sites.
After surgery, recovery can take 2-4 weeks. Pets will need pain medication to control both the pain and inflammation for at least one week. Pets are often given antibiotics after surgery if they had a urinary tract infection. More stones will form if the infection is not cured. Pets will need to be rested for 1-2 weeks following the surgery so they don’t damage the surgical sites or break internal stitches. Urine may be blood-tinged for several days following surgery. Straining to urinate should improve by 2-3 weeks after the surgery.
Lithotripsy, a method to fragment stones into a smaller size so they can be passed or removed through the urinary tract, is extremely uncommon in veterinary medicine. The procedure is only available at a few referral institutions and veterinary schools.
In some cases, usually with very small stones, struvite stones can be dissolved by feeding a prescription diet that acidifies the urine pH and restricts certain minerals such as magnesium and phosphorus. Dissolution of stones can take one week to 2 months, depending on many factors. Calcium oxalate crystals cannot be dissolved with diet, but certain prescription diets can change the urine environment such that enlargement or new stone formation is less likely.
Increasing water intake, either by providing more water or introducing canned food into the diet, can also help treat bladder stones. Increased water allows for increased flushing of the bladder and dilution of minerals within the urine.
If left untreated, bladder stones can grow in size to the point that urination will be difficult or impossible. This is especially problematic if stones pass from the bladder into the urethra and get stuck. Inability to urinate is a life-threatening situation. Other issues associated with bladder stones are chronic pain and increased risk of urinary tract infections.
Once you know your pet can have these stones, prescription diets selected for the specific type of stone can help prevent recurrence. It is extremely important that only the prescription food be fed to the pet. No additional treats (unless specific for the diet), bones, or flavored chew toys can be given. Even a small change in the diet can change the pH and mineral content of the urine and lead to the stones reforming.
Increase water consumption as much as possible to help dilute the urine to further decrease chances of bladder stone formation.
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