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Struvite Bladder Stones in Cats

By Catherine Barnette, DVM

Medical Conditions, Surgical Conditions, Pet Services

What are struvite bladder stones?

Struvite bladder stones are one of the most common bladder stones in cats. These stones are composed of a mineral called struvite, which is a combination of ammonium, phosphate, and magnesium.

Struvite and struvite crystals are a normal finding in urine, at low levels. In some pets, however, these struvite crystals come together to form an actual stone within the urinary tract. These stones can irritate the urinary tract and have the potential to cause a urinary obstruction.

 

What causes struvite bladder stones?

In some cats, struvite bladder stones form as a result of a urinary tract infection. Certain species of urinary bacteria produce a chemical called urease, which leads to changes in urine acidity. Urease-producing bacteria can contribute to the formation of struvite stones.

In most cases however, cats develop struvite stones in the absence of an infection. In these cases, the exact cause is unknown. A number of different factors have been found to contribute to these stones, including the formation of concentrated urine, increased urine pH (alkaline urine), and increased levels of magnesium and phosphorus within the urine.

Struvite stones have been shown to be more common in Siamese cats. This suggests that genetic factors may also play a role.

What are the clinical signs of struvite bladder stones?

Struvite stones, like other bladder stones, cause significant inflammation and irritation of the bladder wall. Therefore, they cause signs similar to those of a urinary tract infection or other inflammatory bladder disease.

Signs of bladder stones typically include frequent urination, straining to urinate, blood in the urine, and urinating outside of the litterbox. Some cats show nonspecific signs of discomfort, such as lethargy and decreased appetite.

In some cats, bladder stones do not produce any symptoms at all. These stones may be detected as part of the workup of another condition.

 

How will my veterinarian diagnose struvite bladder stones?

If your cat is having urinary issues, your veterinarian will first recommend a urinalysis. This test involves obtaining a small urine sample for biochemical analysis and microscopic examination. Struvite stones are most commonly seen in concentrated urine that has an increased pH. On microscopic examination, your veterinarian will likely see red blood cells (caused by irritation of the bladder wall), white blood cells (consistent with inflammation), and increased numbers of struvite crystals.

Your veterinarian may also recommend blood tests, including a complete blood cell count and serum biochemistry profile. These tests will assess your cat’s overall health and rule out other medical conditions that may be contributing to your cat’s urinary signs.

"On radiographs, struvite stones typically look like smooth rocks or pebbles within the bladder."

Finally, your veterinarian will likely recommend abdominal radiographs (X-rays). Radiographs are the most effective way to diagnose bladder stones, because most bladder stones (including struvites) are visible on radiographs. On radiographs, struvite stones typically look like smooth rocks or pebbles within the bladder. Ultrasound may also be used to visualize bladder stones.

What is the treatment for struvite bladder stones?

There are two basic categories of treatment for struvite bladder stones: medical dissolution and surgical removal.

Medical dissolution is accomplished by feeding a specially-formulated prescription diet. These diets are intended to alter the pH and chemical composition of the urine in a way that causes the stone to gradually dissolve. In order for dissolution to be effective, the cat must eat only the prescription food; no treats or other food can be given. Radiographs are repeated every few weeks during this process, to monitor progress and ensure that the stones are shrinking in response to the diet. Most struvite stones will dissolve within one to two months.

"Radiographs are repeated every few weeks during this process, to monitor progress and ensure that the stones are shrinking in response to the diet."

Some cats are unable to eat a prescription diet, due to either a medical conditions or factors in the home. In these cats, bladder stones can be surgically removed in a procedure called a cystotomy. A cystotomy is performed under general anesthesia. Your veterinarian will first make an incision into your cat’s abdomen and then make an incision into the bladder to remove the stones. Once removed, the stones are sent to a laboratory to confirm their chemical composition. Recovery from a cystotomy typically takes one to two weeks. During this time, cats must have their activity restricted to allow their incision to heal. Some abdominal pain and blood in the urine are normal for the first several days after a cystotomy.

Less commonly, bladder stones are removed via a process known as cystoscopy. This involves inserting a small camera into the bladder, with a basket or other retrieval device that can be used to remove the stones. Alternative techniques have also been described to remove bladder stones, but these techniques are less commonly used and are only practical for very small stones.

Will struvite bladder stones recur after treatment?

Cats who have developed struvite bladder stones are likely to experience a recurrence later in life, unless the conditions that led to the formation of stones can be corrected.

The most important step to preventing recurrence is to feed a prescription diet. These diets are specially formulated to create a urine environment that is less favorable for the formation of struvite bladder stones. In general, these diets decrease the urine pH and restrict the levels of magnesium, ammonium, and phosphorus in the urine.

"The most important step to preventing recurrence is to feed a prescription diet."

Additionally, you will need to increase your cat’s water intake in order to make your cat’s urine less concentrated. In most cases, using the canned version of your cat’s prescription diet will keep the urine dilute. In some cases, you may need to take additional steps, such as adding a running water fountain to your home, offering flavored water (a small amount of chicken broth or tuna juice can be used), or adding additional water to canned food.

Your cat will require long-term, regular rechecks. This will allow your veterinarian to monitor your cat’s urine, in order to ensure that her urine characteristics remain within desired parameters. Regular monitoring will also allow future recurrence of bladder stones to be detected early, when treatment may be easier and more effective.

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