Calcium Oxalate Urolithiasis in Dogs

Urolithiasis is a disorder in which minerals in the bladder clump together and form crystals or stones in the urine. Calcium oxalate stones are composed of the mineral calcium oxalate and do not dissipate once they are formed. Occasionally these structures travel into the urinary tract and either partially or completely block the passage of urine. This can cause severe distress to your pet and should be considered an emergency. Surgery is often required to resolve this condition, and changes in diet may be needed to keep the obstruction from reoccurring.

Calcium oxalate urolithiasis is a disorder in which calcium oxalate stones, or crystals, form in the bladder and block the passage of urine out of the body.

Calcium oxalate urolithiasis, or the presence of calcium oxalate crystals anywhere within the urinary tract, may initially develop with no outward symptoms if the crystals do not get large enough to obstruct the urinary tract. When blockages do occur the following signs and symptoms may be observed, and should be considered an urgent medical condition:

• Blood in the urine
• Cloudy urine
• Depression
• Distended abdomen
• Foul-smelling urine
• Frequent urination
• Inability to urinate
• Inappropriate elimination
• Loss of appetite
• Pain, particularly during urination
• Straining 
• Vomiting
• Weakness

Types 

A glycoprotein called nephrocalcin in your pet’s urine is responsible for preventing the formation of crystals in the urine. In many cases, the nephrocalcin production is defective, and there is evidence that this is in part genetically driven. 

Breeds that are more prone to developing calcium oxalate urolithiasis include:

• Bichon Frise
• Cairn Terrier
• Chihuahua
• Dachshund
• Keeshond
• Lhasa Apso
• Maltese
• Miniature and Toy Poodle 
• Miniature Schnauzer
• Papillion
• Pomeranian
• Jack Russell Terrier
• Shih Tzu
• Standard Schnauzer
• West Highland White Terrier
• Yorkshire Terrier

The Cocker Spaniel, German Shepherd, and Golden Retriever breeds are less likely than other breeds to develop this type of urolithiasis.

Although breed disposition can play a large part in the formation of the calcium oxalate crystals that cause urolithiasis, it is not the only component to this disorder. Male dogs are much more likely to develop this disorder than females, and the most likely age to develop this type of stone is between five and twelve years old. Several disorders can contribute to their formation as well as general condition status; dogs with inadequate fluid intake or obese animals are more likely to develop the calcium oxalate stones. Hypercalciuria is elevated calcium levels in the blood and can lead to developing calcium oxalate stones, as can other metabolic diseases like Cushing’s Disease. Excessive dairy, protein, or sodium in the diet can also result in a higher than average amount of calcium in the bladder, and corticosteroids and diuretics can also increase the risk of calcium oxalate stones.

When you bring your canine into the veterinary clinic with symptoms related to calcium oxalate urolithiasis, general blood tests such as a biochemistry profile as well as a complete blood count will be ordered, and a urinalysis will be completed as well. Results from the urinalysis may show signs such as acidic urine, and sometimes even visible crystals and the blood tests will help to confirm the functionality of the kidneys. The veterinarian will also palpate the bladder area to check for any stones large enough to be detected manually.

Imaging techniques such as x-rays or ultrasound are often used to visualize the size and location of stones, particularly those crystals too small to feel by palpitation. These tests can all be done to verify that stones are present, what size they are, and where they are located. They will not, however, determine the mineral composition of the stones that are causing the blockage, although educated guesses can be made. The mineral composition of the crystals affecting your pet will need to be analyzed in the laboratory in order to determine the best possible treatment plan.

Unlike other types of mineral crystals that may be present in the kidneys or in the bladder, calcium oxalate stones are unable to be dissolved once they have formed and may need to be removed through surgery. It is important to try and remove even small stones of this type, as they can irritate the lining of the bladder if left unchecked. This irritation can lead to a thickening of the bladder walls or to bladder infections. If the crystals are small, they may be able to be removed using a technique called urohydropropulsion. In this procedure, a saline solution is passed up through a catheter in order to increase the liquid volume in the bladder and propel the stones out. This method is more successful in female dogs over twenty pounds and does run a small risk of physical damage to the bladder. The likelihood of damage to the urethra is greater in male dogs due to the bone surrounding their urethra, called the os penis, which limits the elasticity of the urethra.

In some cases, a retrograde urohydropropulsion will be used to push the stone back into the bladder for removal from there. Stones in the bladder can either be removed by lithotripsy, a procedure that targets the stone using shockwaves, or by surgical removal from the bladder itself. Calcium oxalate stones are usually easier to fracture using lithotripsy than other types of urinary stones but requires specialized expertise and equipment, and is not available at all clinics.

The formation of calcium oxalate crystals and stones in the bladder tends to reoccur if underlying problems is not addressed. Measures will be taken to reduce the acidity in the urine to prevent new stones from forming, including changing your dog’s diet to include higher  levels of potassium, magnesium, phosphorus, and chloride, and ensuring that your dog is getting higher levels of hydration than they previously were. Your veterinarian will likely request urinalysis testing to be done every few months and if dietary changes are not successful in preventing further stones from forming, potassium citrate or thiazide diuretics may need to be added to your pet’s daily regimen. In rare cases, some male dogs that continually develop this type of crystal may require additional surgery to create a new urinary opening to help prevent future obstructions.