My dog has urate bladder stones. What are they?
Bladder stones (uroliths or cystic calculi) are rock-like formations of minerals that form in the urinary bladder and are more common than kidney stones in dogs. There may be a large, single stone or a collection of stones that range in size from sand-like grains to gravel.
There are two main causes of urate stones: a genetic defect in the metabolism of uric acid, which is most commonly seen in dalmatians, and a liver disease called a portosystemic shunt (abnormal blood vessel bypassing the liver). If urate bladder stones or crystals are diagnosed in a dog that is not a Dalmatian, the dog should be tested for the presence of a liver shunt.
How common are urate bladder stones?
While bladder stones are somewhat common in dogs, urate stones constitute only about 5% of all bladder stones diagnosed. Breeds most diagnosed with urate bladder stones include dalmatians, English bulldogs, and black Russian terriers. In these breeds, genetic testing should be performed prior to breeding to reduce the occurrence of this condition. Urate bladder stones are more common in male (97%) than female (3%) dalmatians.
What are the signs of urate bladder stones?
The general signs of bladder stones are similar to the signs of a bladder infection or cystitis. The most common signs that a dog has bladder stones are blood in the urine and straining to urinate.
"If an obstruction occurs, the bladder cannot be emptied fully; if the obstruction is complete, the dog is unable to urinate at all."
Blood in the urine occurs because the stones rub against the bladder wall, irritating and damaging the tissue and causing bleeding. Straining to urinate may result from muscle spasms, from a physical obstruction to urine flow, or from inflammation and swelling of the bladder walls or the urethra (the tube that transports the urine from the bladder to the outside of the body).
Large stones may act almost like a valve or stopcock, causing an intermittent or partial blockage where the bladder attaches to the urethra. Small stones may flow with the urine into the urethra where they can become lodged and cause an obstruction.
If an obstruction occurs, the bladder cannot be emptied fully; if the obstruction is complete, the dog is unable to urinate at all. If the obstruction is not relieved, the bladder may rupture or the kidneys may fail. A complete obstruction is potentially life threatening and requires immediate emergency treatment.
If urate bladder stones form because of a portosystemic shunt, the dog may also show signs of neurologic impairment (dullness or disorientation, head pressing, or seizures).
How are urate bladder stones diagnosed?
The initial step with any urinary tract problem is for your veterinarian to analyze a sample of your dog’s urine. A urinalysis assesses the chemistry of the urine and looks at it under the microscope. Urate crystals may be found in the urine, which have a characteristic color and shape. Other possible findings in a dog with urate stones are blood in the urine, protein in the urine, white blood cells in the urine, or an acidic pH.
In some cases, if your dog is relaxed and the bladder is not too painful, your veterinarian may be able to feel stones in the bladder. However, some stones are too small to be felt this way.
Unfortunately, urate bladder stones often do not show up on regular X-rays. This means that your veterinarian will need to perform other imaging studies to detect these stones, such as a bladder ultrasound or contrast X-rays (a specialized technique that uses dye to outline the stones in the bladder). Your veterinarian may recommend one of these specialized imaging studies if they are concerned that your dog may have urate bladder stones based on breed, results of a urinalysis, and/or results of blood tests that indicate a liver problem.
The only way to be sure that a bladder stone is a urate stone is to have the stone analyzed at a veterinary diagnostic laboratory. In some cases, your veterinarian may make an educated guess about the type of stone that is present, based on the findings of imaging studies and results of a urinalysis and/or blood tests.
"The only way to be sure that a bladder stone is a urate stone is to have the stone analyzed at a veterinary diagnostic laboratory."
For example, if ultrasound or contrast X-rays show that there are one or more stones present in the bladder, and the results of the urinalysis show the presence of acidic urine and numerous urate crystals, your veterinarian may make a presumptive diagnosis of urate bladder stones and start treatment accordingly.
How are urate bladder stones treated?
There are two primary treatment strategies for treating urate bladder stones in dogs: medical dissolution and physical removal.
Medical dissolution involves feeding a very specific prescription diet. These diets are lower in protein and promote a higher urine pH. Canned foods are preferred, as they produce a more dilute urine due to higher water content. Stones are less likely to form in diluted urine. Certain medications may also be prescribed, such as allopurinol to decrease urate production and potassium citrate to increase the pH of urine.
It is important to note that dissolution only works if the stones are purely urates. Often, stones can be a combination of different substances, especially if secondary infection is present. Attempting dissolution is not appropriate if a partial or full obstruction is present, in which case immediate removal would be necessary.
"Attempting dissolution is not appropriate if a partial or full obstruction is present, in which case immediate removal would be necessary."
Removal may be done in several ways. In some cases, small stones may be removed non-surgically by urohydropropulsion, in which the stones are flushed out of the bladder using a special urinary catheter technique. This method is only possible when the stones are very small in diameter. If your veterinarian has a cystoscope, small stones in the bladder or urethra can sometimes be removed with this instrument, therefore avoiding a surgical procedure to open the bladder.
Surgical removal is commonly recommended in cases where the bladder stones are too large for urohydropropulsion, when there are many stones present in the bladder, or if there is an increased risk of urinary obstruction. This method is the quickest way to treat bladder stones; however, it may not be the best option for patients that have other health concerns or in whom general anesthesia could be risky. With this option, the stones are removed via a cystotomy: a surgical procedure to access and open the bladder so that the stones can be removed. This routine surgery is performed by many veterinarians and dogs usually make a rapid postoperative recovery.
"If the stones have obstructed the urethra such that your dog is unable to urinate, emergency surgery must be performed immediately to save your dog's life."
If the stones have obstructed the urethra such that your dog is unable to urinate, emergency surgery must be performed immediately to save your dog's life. Your veterinarian will discuss the pros and cons of each of these options with you and help you decide which option is best in your dog's situation.
In some selected referral centers, a third option may be available to treat urate bladder stones: ultrasonic dissolution. With this technique, high frequency ultrasound waves are used to disrupt or break the stones into tiny particles that can then be flushed out of the bladder. This option is not widely used due to its lack of availability. It has the advantage of immediate removal of the offending stones without the need for surgery or general anesthesia. Your veterinarian will discuss this treatment option with you if it is available in your area.
How can I prevent my dog from developing urate bladder stones in the future?
Dogs that have experienced urate bladder stones will often be fed a therapeutic diet for life. Dogs with liver disease will need to be treated appropriately prior to addressing urate bladder stone management. Diets that are lower in protein and therefore lower in purines (one of the building blocks of urate crystals) and that promote higher urine pH are recommended.
It is very important to encourage water consumption, as dilute urine (urine specific gravity less than 1.020) helps decrease urate stone formation. In certain cases, medications such as allopurinol may be required long term. In addition, careful, routine monitoring of the urine to detect any signs of bacterial infection is also recommended.
Bladder X-rays and urinalysis will be performed one month after treatment and then every three to six months for life. Many dogs will need to have a bladder ultrasound to detect early urate stones that are small and may not be visible on X-rays.
Dogs displaying any clinical signs of urinary tract infections such as frequent urination, urinating in unusual places, painful urination, or the presence of blood in the urine should be evaluated immediately.