What is Urolithiasis - bladder stones?

Definition: Urolithiasis is by definition the formation of stones in the bladder. Bladder stones are sometimes called uroliths or calculi. Stones form in the bladder after crystalluria has occurred. If you have questions on crystalluria please consult our handout entitled crystalluria. There are many types of stones. The two most common are struvite and calcium oxalate. Because there are so many types of stones, we will concentrate on these two most common types.

Why do they form?

Stone formation is due to many reasons:

• Struvite stones which commonly form in an acid pH of urine, ocurr when magnesium and phosphate ratios are out of balance, when the pH is too high, and bacteria are present. The more concentrated the urine, the higher the crystal count. These minerals become supersaturated, and precipitate out into stones. Crystals lead to stone formation. In the case of calcium oxalate crystals, hypercalcuria (high urine calcium), hyperoxaluria (high urine oxalate), and variable pH can also be a factor. Specific causes of sterile struvite uroliths are unknown.

• Calcium oxalates are more difficult to control than struvite crystals. In both cases bacterial infections complicate and increase the likelihood of stone formation.

Are they genetic?

While there is no known genetic link to calcium oxalate formation, we do see an increased incidence of struvite crystals in some breeds, especially miniature schnauzers and English cocker spaniels. Some breeds are more prone to stone formation although the heritability is not known. In the case of struvite crystals, commonly affected breeds are the

• miniature schnauzer
• Shih Tzu
• Bichon frises
• miniature poodle
• cocker spaniel
• Lhasa apso
• several other breeds.

• miniature schnauzers
• Lhasa apsos
• Yorkshire terriers

Any age of dog or cat can be affected by crystals and therefore affected by stone formation. The predominance of struvite crystals appear to be more common in females(85%), while calcium oxalate crystals appear to be more common in males. (male dogs-73% and male cats-55%) Because stones take time to form, it is uncommon to find stones in young dogs, however, stones can form in as little as 2 weeks. The older the pet, the more likely it is to form stones.

What are the symptoms?

How are bladder stones diagnosed?

On physical examination, in some cases, stones can be palpated. Unfortunately, many times the stones are either very small or only a few in number, and difficult to palpate. Even a few stones can cause severe symptoms for your pet.
In the case of male cats, obstruction is common and generally seen even with just large crystals - well before stone formation has occurred. Urinalysis is important for the diagnosis of what type of crystal is present, as most stones form from the crystals present in the urine. This can give us a heads up on what kind of diet change will be needed.

Stones are often found on ultrasound. The Ultrasound is often used in collecting urine samples. Ultrasound guided cystocentesis is often preformed, as it is safe and gives us a sterile urine sample. Urine samples collected by cystocentesis are collected sterilely and therefore do not contain contaminants from the outside world.

X-ray is sometimes also required for stone diagnosis. Struvite uroliths are radiodense and may be detected by survey radiography.This is especially true if we have small stones. Occasionally, this may require a double contrast pneumocystogram to diagnose it. Double contrast pneumocystograms are dye studies which help us determine if there is a stone present and whether or not the bladder wall is thickened. With the advent of ultra-sonography, double contrast pneumocystograms are performed less frequently.

Once stones have formed we often need to remove them. Stone analysis will be performed on the removed stones to give us an exact diagnosis of which type of stone type your pet has.

How are bladder stones treated?

After the stones have formed, it is difficult to treat them without surgically removing them. In rare cases of struvite stones - special diets can be tried. Unfortunately, it is uncommon for diet to adequately remove the stones. While the pet is on a special diet for stone dissolution, it is necessary to continue antibiotics. It is not uncommon for special diets to require more than six months and up to a year to dissolve stones. During that time your pet will continue to be uncomfortable and have blood in the urine. For that reason surgery is generally recommended.
During surgery, the doctor will surgically remove the stones from the bladder. The stones will then be sent off for analysis. The surgery for stone removal is called cystotomy.

After stone removal, a special diet will be needed to prevent further formation of stones. Most special diets are prescription diets. It is very important to feed strictly the diet - without any treats or snacks. If you have questions about the special diet, please consult your veterinarian.

It is very common for stones to cause bacterial infections; therefore, antibiotics are also commonly used to clear up any bacterial infection that is present. Sometimes a culture and sensitivity is needed to select the correct antibiotic. This test is the growing of the bacteria in the urine. Antibiotics are then tested on the culture to select the one that works best.

The calcium oxalate stones tend to be difficult to dissolve and keep from reforming. New research shows that some medications may be beneficial in this. Many medications are purely experimental at this stage, though they have been shown to be helpful. Your veterinarian will consult with you if your pet needs a special medication.

Are there any complicating factors?

As mentioned before, some complications can occur due to stones which cause obstruction of the urinary tract. This is called a blockage, and is life threatening. If your pet has been blocked, special blood work will also be needed. Blockages often lead to renal failure (kidney disease). Renal failure can lead to permanent, lifelong debilitation. It is important to treat crystalluria and urolithiasis early in order to prevent these complications.

The male cat is particularly prone to blockage (inability to urinate). If you see your cat straining in the litter box to urinate, check to be sure urine is coming out. If not, this should be considered an emergency and treated immediately. If you ever have doubts as to whether or not your pet can urinate properly, please contact us immediately for an examination. If your pet is blocked (meaning that there is a stone or crystal lodged in the urethra), anesthesia and catheterization will be needed to relieve the obstruction. Once the obstruction is relieved, we still need to treat the underlying cause. Surgery, medication and diet changes may be necessary. In cats especially, if diet and medication cannot control the recurrence of blockage, a special surgery called perineal urethrostomy (P.U.) will be recommended. More information about the surgeries is available from the veterinarian and in the form of handouts online.

Some commonly asked questions.

I have a cat who has blocked several times, what can be done to stop blockage?

There is a surgery called perineal urethrostomy (P.U.). In essence this is a sex change operation for cats. The penis has a very narrow urethra. Because it’s very narrow, it tends to obstruct easily. As the penis enters the bladder, the urethra widens. In this location blockages are unlikely. The surgery removes the narrow part of the penis, opening up at the wider part so that urine and crystals are unlikely to block the urethra. Cats do very well with the surgery and it can be lifesaving.