Bladder stones, also known as uroliths, can cause significant discomfort and complications for dogs. Detecting these stones, whether through noticeable urinary issues or incidentally, is crucial, as they can lead to persistent infections, urinary obstruction, and ongoing pain if left untreated. Implementing preventive measures is key to avoiding the formation of new stones.
Calcium oxalate stones are a common concern, particularly in certain breeds and demographics. Approximately 73% of dogs diagnosed with calcium oxalate stones are male. Breeds at a higher risk include miniature schnauzers, Lhasa apsos, Yorkshire terriers, miniature poodles, Shih Tzus, and Bichon Frises. The majority of cases occur in dogs between 5 and 12 years of age.
Diagnosing Calcium Oxalate Stones
While a urinalysis can offer clues, the definitive diagnosis of calcium oxalate bladder stones requires laboratory analysis of a retrieved stone. Small stones may be obtained through urinary bladder flushing and forceful expression. Other methods for stone retrieval include surgical removal, endoscopic retrieval via the urethra, or laparoscopic extraction through a small abdominal incision. Unlike struvite or uric acid stones, calcium oxalate stones cannot be dissolved through dietary changes alone.
Understanding the Cause of Calcium Oxalate Stones
A strong hereditary component is often implicated in the formation of oxalate bladder stones, mirroring the situation in humans. A naturally occurring substance in urine, called “nephrocalcin,” inhibits the formation of these stones. In individuals prone to calcium oxalate stone formation, this substance may be defective due to a genetic issue.
In humans, genetic predisposition is often compounded by dietary factors, with foods like spinach, peanuts, chocolate, dairy, and certain supplements contributing to stone formation. Dogs, however, typically consume a more consistent diet of commercial dog food, making genetics the more dominant factor.
Certain metabolic diseases can also predispose dogs to calcium oxalate stones. For instance, Cushing’s disease leads to excess cortisol production, increasing calcium excretion in urine and promoting stone formation. Similarly, elevated blood calcium levels (hypercalcemia) can result in increased urinary calcium. Screening for such underlying medical conditions is an important part of the diagnostic workup.
The Risks of Bladder Stones
The most immediate danger posed by bladder stones is urinary obstruction, especially in male dogs due to the “os penis” structure in their urethra, which cannot expand to accommodate a stone. This can lead to life-threatening uremic poisoning. If obstruction occurs, veterinary intervention is required to dislodge or surgically remove the stone.
Beyond obstruction, bladder stones irritate the sensitive lining of the bladder, causing bleeding and significantly increasing the risk of chronic bladder infections.
Management and Prevention of Calcium Oxalate Stones
Since calcium oxalate stones cannot be dissolved by diet, surgical removal is typically necessary. Studies indicate that a significant percentage of dogs that undergo stone removal will develop new stones within three years without proper preventive measures. A comprehensive therapeutic plan is essential to minimize the chance of recurrence.
Step One: Diet Modification
While not capable of dissolving existing stones, special diets are crucial for preventing new ones. The goal is to create a urinary environment with reduced levels of calcium and oxalate, and a urine pH unfavorable to calcium oxalate formation. High-protein, high-sodium diets should be avoided, as they can increase calcium absorption.
Recommended therapeutic diets include Hills G/D, Hills U/D (with caution for specific heart conditions), Hills C/D multicare, Hills Science Diet Adult 7+ Chicken & Barley Entree, and Royal Canin S/O. Opting for canned versions of these diets is advisable to encourage water consumption and urine dilution. It is vital to avoid table scraps for dogs prone to oxalate stones. Acceptable treats include plain cooked chicken or turkey, eggs, rice, peas, pasta, white potatoes, cabbage, cauliflower, bananas, and melon. Consulting a veterinary nutritionist for home-cooked diet recipes can be beneficial.
Certain medications can increase the risk of calcium oxalate stone formation and should be avoided if possible. These include prednisone and other cortisone-type medications, as well as furosemide (a diuretic used for heart failure). Both increase urinary calcium. Thiazide diuretics are a better choice if a diuretic is necessary. Supplementation with Vitamin D or C also increases the risk and should be discontinued.
Step Two: Monitoring Urinalysis and Radiographs
Two to four weeks post-surgery, a urinalysis and bladder radiographs are performed. If the urine specific gravity is not adequately dilute (less than 1.020), increasing water intake is recommended. If the urinary pH is below 6.5 or oxalate crystals are present, proceed to Step Three. Otherwise, regular urinalysis every 3-6 months and radiographs every 6-12 months are advised for life to detect new stones early.
Step Three: Potassium Citrate Supplementation
Oral administration of potassium citrate increases citrate levels in the urine. Citrate binds with calcium, forming calcium citrate, which tends to remain dissolved, unlike calcium oxalate. Potassium citrate also helps create alkaline urine, making it harder for calcium oxalate stones to form. It is typically administered twice daily.
Step Four: Follow-up Urinalysis
Two to four weeks after starting potassium citrate, another urinalysis is conducted. Again, if the urine is not dilute or the pH is below 6.5, water intake should be increased. If parameters are within the desired range, continued monitoring with urinalysis and radiographs every 6-12 months is recommended. If the patient remains predisposed to stone formation, proceed to Step Five.
Step Five: Thiazide Diuretics
Thiazide diuretics increase urine production while reducing the calcium content in the urine. This medication is usually given twice daily, and electrolyte levels are monitored via blood tests within the first two weeks of treatment.
For some dogs, stone formation may continue despite all efforts. Consistent radiographic monitoring is crucial for detecting new stones while they are still small. As research progresses, new advancements may emerge. Until then, these guidelines, developed by specialists at the University of Minnesota, are essential for oxalate stone prevention.
A Special Note on Bichon Frises
Bichon Frises appear to have a particularly high recurrence rate for oxalate bladder stones, with some studies showing a significant percentage of dogs developing new stones shortly after surgical removal. Preventive measures must be particularly aggressive from the outset for this breed due to their significantly higher risk compared to other breeds.
Preventing Male Dog Obstruction
In male dogs, the “os penis” can obstruct stone passage. A surgical procedure called a urethrostomy can create a new, wider urinary opening in the scrotal area, allowing urine to exit earlier and preventing stones from lodging in the os penis. This procedure typically requires neutering the dog. While not a cure for stone recurrence, it effectively prevents life-threatening obstructions.
Laser Lithotripsy
Laser lithotripsy is a newer technique that uses a laser to break stones into smaller, passable fragments. This method is particularly useful for a small number of stones or when a stone is lodged in the urethra. While less invasive for suitable patients, it may be time-consuming for a large stone burden.
Calcium oxalate bladder stones can be a frustrating challenge due to their tendency to recur. Consistent monitoring is essential, and owners must weigh the cost and effort of regular veterinary visits against the significant expense and complications of recurrent stone surgeries.
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