What are bladder stones (Uroliths, Urolithiasis)?
One of the functions of the kidneys is to eliminate waste material from the body in liquid form (e.g. urine). However, some of this waste material is only slightly soluble, and can easily precipitate into small crystals. Over time these crystals can increase in size, forming uroliths or bladder stones.
Although uroliths are commonly referred to as bladder stones, they can actually occur anywhere in the urinary tract (i.e. the kidneys, ureters, bladder, or urethra). The stones can made up of a variety of mineral components, and this will affect the measures needed to be taken to control them.
The most common type of bladder stone found in the cat and dog is made up of struvite, which contains magnesium, phosphate, and ammonium. As the uroliths grow in size, they can irritate and block the urinary tract, preventing the normal flow of urine.
What factors contribute to the formation of uroliths?
Bladder stones will not form unless there is a sufficiently high concentration of certain minerals in the urine, the crystals spend a prolonged period in the urinary tract, and the pH of the urine is favorable to urolith formation. There are a number of risk factors that contribute to the likelihood of developing stones in the urinary tract:
1. Diet: The food your pet consumes can affect the mineral content of its urine (i.e. by containing high levels of calcium, magnesium, phosphate, etc.), alter the acidity of its urine (leading to growth of certain types of stones), or the moisture content of the diet can alter the concentration of the urine.
2. Urinary Tract Infection (UTI): Certain bacteria that infect the urinary tract can lower the pH of the urine, resulting in an ideal environment for the growth of struvite stones.
3. Low Water Intake: The less water your pet consumes, the more concentrated its urine will be. Uroliths and urethral plugs are more likely to develop in concentrated urine than dilute urine.
4. Frequency of Urination: The abnormal retention or urine promotes the formation of uroliths.
5. Genetics: The higher prevalence of uroliths in certain breeds tends to suggest a hereditary predisposition to develop particular types of bladder stones. These predisposed breeds include Bulldogs, Dalmatians, Miniature Schnauzers, and Yorkshire Terriers.
6. Gender: Struvite bladder stones are found predominantly in female dogs, whereas other types of bladder stones more commonly affect male dogs. In cats, urolithiasis occurs equally in both sexes. However, females are more likely to develop struvite stones, while males are prone to struvite urethral plugs because of the narrow diameter of their urethras.
How can I recognize whether my pet has bladder stones?
Depending on the size and location of the bladder stones, there may be a range in symptoms from no noticeable signs, a cystitis (inflammation of the bladder) or urethritis (inflammation of the urethra), to a complete blockage of urine flow, which is a life-threatening situation.
Signs to look out for are:
• Pain when urinating
• Straining to pass urine
• Difficult, slow urination
• Frequent unsuccessful attempts to urinate
• Blood in the urine
• Incontinence
• Abdominal discomfort
• Anorexia and vomiting (especially in cats with obstructions)
• Drinking more than usual
If you suspect your pet has bladder stones, do not hesitate to contact your veterinarian. This is a painful condition that should be resolved as soon as possible. Furthermore, the signs or bladder stones are similar to other serious diseases, such as kidney disease, that may require immediate treatment.
How does the veterinarian diagnose bladder stones?
Your pet’s medical history, along with a thorough physical exam, may alert your veterinarian to the possibility of bladder stones. But, further tests are necessary to confirm the diagnosis:
• Urinalysis: analysis of a urine sample can reveal the presence of bacteria in the urine, the pH of the urine, and the specific type of crystal present in the urine
• Diagnostic imaging: X-rays of the abdomen can reveal certain types of stones in the urinary tract, depending on the mineral composition of the stone. Not all uroliths can be detected by x-rays, so an ultrasound scan may be required as well. Imaging allows the vet to determine exactly where in the urinary tract the stones are actually located, and the size of the stones.
• Blood sample: often a blood sample is required from animals that seem particularly ill just to ensure that there are no concurrent systemic illnesses.
• Stone analysis: Analysis of a stone that has been passed in the urine or surgically removed from your pet will provide a definitive diagnosis of the mineral composition of the uroliths.
Once the vet has confirmed the presence of bladder stones, and determined the mineral composition of the stones, he or she can then develop a treatment plan specific to your pet.
How are bladder stones treated?
The treatment plan for your pet will depend on the type of stone it has and the severity of disease. While some cases can be managed medically, others will require surgical removal of the stones. Medical management to dissolve the stones usually involves a course of antibiotics to resolve any bacterial infection and feeding a specially formulated diet designed to break down bladder stones.
Hills Prescription Diet makes a number of different foods for cats and dogs that dissolve stones and maintain the correct urine pH. Urine acidifiers can also be utilized to achieve the correct urine acidity. Some animals may need to be on a prescription diet for some time to prevent the recurrence of bladder stones.
In order to ensure the efficacy of treatment, your pet will require follow-up monitoring to ensure that the stones have been effectively dissolved. This may involve further urinalysis, a urine culture, and/or x-rays.
(photo: rljohnson)