Cystine Bladder Stones in Dogs

By Malcolm Weir, DVM, MSc, MPH; Tammy Hunter, DVM; Ernest Ward, DVM

My dog has cystine bladder stones. What are they?

Bladder stones (also called 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. A somewhat rare form of bladder stone in the dog is composed of cystine crystals.

How did my dog develop cystine bladder stones?

Cystine bladder stones appear to be the result of a genetic abnormality that prevents a dog from reabsorbing cystine from the kidneys. This type of stone has been reported in over 60 breeds of dogs, with the condition believed to be inherited in some breeds like the Newfoundland, Labrador retriever, Australian cattle dog, and miniature pinscher.

How common are cystine bladder stones?

While bladder stones in general are somewhat common in dogs, cystine bladder stones are rare. Cystine uroliths are most diagnosed in male dogs (98% of dogs diagnosed with cystine bladder stones are male).

What are the signs of cystine bladder stones?

The signs of bladder stones are very similar to those of an uncomplicated bladder infection or cystitis. The most common signs that a dog has bladder stones are hematuria (blood in the urine) and dysuria (straining to urinate).

"A complete obstruction is potentially life threatening and requires immediate emergency treatment."

Hematuria occurs because the stones rub against the bladder wall, irritating and damaging the tissue and causing bleeding. Dysuria may result 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), from muscle spasms, or from a blockage of urine flow caused by the presence of the stones. Dogs may demonstrate signs of discomfort by being less active, panting more, eating less or crying when urinating.

Large stones may act almost like a ball valve, causing an intermittent or partial obstruction at the neck of the bladder, 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 will be unable to urinate at all. If the obstruction is not relieved, the bladder may rupture.A complete obstruction is potentially life threatening and requires immediate emergency treatment.

How are cystine bladder stones diagnosed?

In some cases, if the dog is relaxed and the bladder is not too painful, your veterinarian may be able to feel cystine bladder stones in the bladder. However, some cystine bladder stones are too small to detect this way.

Unfortunately, many cystine stones are radiolucent, meaning they are not visible on X-rays (radiographs). Your veterinarian may need to perform other imaging, such as a bladder ultrasound or a contrast radiographic study, a specialized technique that uses dye to outline the stones in the bladder. If your veterinarian suspects that your dog has cystine bladder stones based on breed, clinical signs, and results of a urinalysis, one or both of these specialized imaging techniques may be recommended.

"The only way to be certain that a particular bladder stone is a cystine bladder stone is to have it analyzed at a veterinary diagnostic laboratory."

The only way to be certain that a particular bladder stone is a cystine bladder stone is to have it analyzed at a veterinary diagnostic laboratory. In some cases, your veterinarian may make a presumptive diagnosis about the type of stone based on the findings on imaging studies and results of a urinalysis. For example, if your dog is one of the breeds predisposed to this type of stone, if ultrasound or contrast X-rays show that there are one or more stones present in the bladder, and if the results of the urinalysis show the presence numerous cystine crystals, your veterinarian may make a presumptive diagnosis of cystine bladder stones and start treatment accordingly.

How are cystine bladder stones treated?

There are two primary treatment strategies for treating cystine bladder stones in dogs.

Medical management

If there is no urinary obstruction, cystine bladder stones can be dissolved through dietary therapy. The goal of this treatment is to reduce the concentration, and increase the solubility, of cystine in the urine. Feeding a low protein, low sodium diet can aid in this approach. Prescription diets such as Hill’s U/D, or Royal Canin UC Low Purine are recommended.

Since cystine crystals don’t form well when urine pH is higher than 7.2 (more alkaline), your veterinarian may recommend urine alkalinizing agents like potassium citrate, in addition to prescription diet. A drug called 2-Mercatopropionylglycine (2-MPG, or tiopronin) that decreases cystine crystal formation is also sometimes prescribed. Your veterinarian can discuss the advantages and disadvantages of these medical treatments.

Physical removal of stones

In selected cases, small stones may be removed non-surgically by urohydropropulsion, in which the bladder stones are flushed out of the bladder using a special urinary catheter technique. This technique is possible only when the stones are very small in diameter. Small stones in the bladder can sometimes be removed with a cystoscope, avoiding the need for surgery to open the bladder. These procedures may sometimes be performed with your dog under heavy sedation, although general anesthesia is often necessary. Either of these non-surgical procedures may be used to obtain a sample stone for analysis so that your veterinarian can determine if dietary dissolution is feasible.

Surgical removal is commonly recommended in cases where the bladder stones are too large for urohydropropulsion, when there are many stones in the bladder, or if there is an increased risk of urinary obstruction. Surgical removal is the quickest way to treat bladder stones; however, it may not be the best option for patients with other health concerns, or in whom general anesthesia could be risky. With this option, the stones are removed via cystotomy, which means that the bladder is surgically exposed and opened so that the stones can be removed. This routine surgery is performed by many veterinarians and dogs usually make a rapid post-operative recovery. If the stones have obstructed the urethra and the dog is unable to urinate, emergency surgery must be performed immediately to save the dog's life.

"If the stones have obstructed the urethra and the dog is unable to urinate, emergency surgery must be performed immediately to save the dog's life."

In some selected referral centers, another option may be available to treat bladder stones: ultrasonic dissolution (lithotripsy), a technique in which high frequency ultrasound waves are used to disrupt or break the stones into tiny particles that can then be flushed out of the bladder. It has the advantage of immediate removal of the offending stones without the need for surgery. Your veterinarian will discuss this treatment option with you if it is available in your area.

Your veterinarian will discuss the advantages and disadvantages of each treatment option with you, and help you decide which option is best in your situation.

How can I prevent my dog from developing cystine bladder stones in the future?

Unfortunately, cystine stones have a high rate of recurrence, despite careful attention to diet and lifestyle. Dogs that have developed cystine bladder stones in the past will often be fed a therapeutic diet for life (see handout “Nutritional Concerns for Dogs with Bladder Stones” for more information). In addition, careful routine monitoring of the urine to detect any signs of bacterial infection is also recommended.

Bladder X-rays and urinalysis will typically be performed one month after treatment and then every three to six months for life. Dogs displaying any clinical signs such as frequent urination, urinating in unusual places, painful urination, or the presence of blood in the urine should be evaluated immediately.

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