Kidney Stones in Dogs

All dogs are susceptible to developing kidney stones, though some breeds are more susceptible to certain types of stones. Kidney stones can be painful and lead to urinary tract inflammation, infection, tissue damage and possible urinary tract obstruction. Kidney stones, also known as nephroliths, are crystal formations in the kidneys resulting from the concentration of mineral salts in the urine. Stones can also form in the bladder, ureters or urethra. If you suspect your pet is having symptoms of kidney stones, schedule an veterinarian appointment as soon as possible. If you can, collect a sample of urine in a container directly from the stream of urine.

Stones may not cause symptoms at all. Symptoms that may be observed are similar to those involved with urinary tract infections and include:

• Blood in the urine
• Urinating in odd places
• Licking at genitals
• Pain during urination
• Straining to urinate
• Frequent urination producing only small amounts
• Recurrent urinary tract infections
• Abdominal pain

Types

Kidney stones form from the precipitation of mineral salts. The type of salt that the crystal is formed from defines the kidney stone type, though some stones can be formed from more than one type of salt.  Kidney stones can be made up of several types of minerals, including:

• Uric acid
• Calcium oxalate
• Struvite (magnesium ammonium phosphate)
• Cystine
• Calcium phosphate

The normal urine of a dog is slightly acidic and contains dissolved mineral products. As long as the urine remains dilute and at the correct pH, mineral salts remain in solution. If the pH of the urine becomes too acidic or alkaline or the urine becomes too concentrated, crystals of salt will precipitate out and form stones. The causes of kidney stone formation can include one or more of the following:

• Increased mineral salt concentration in the urine (can result from diet or urinary tract infection).
• Increased water reabsorption by the kidneys
• Changes in urine pH (can result from diet or urinary tract infection)
• Urinary tract infection – bacteria produce urease, an enzyme that breaks down urea in dog urine resulting in a more alkaline urine pH.
• Long term use of diuretics
• Dehydration
• Genetic predisposition - breeds include (but are not limited to) the bichon fries, lhasa apso, miniature schnauzer, and Yorkshire terrier.

If you suspect your pet is having symptoms of kidney stones, visit the veterinarian as soon as possible. If you can, collect a sample of urine in a container directly from the stream of urine. Keep the urine in the refrigerator until your appointment. Samples over 24 hours old may not be useful for analysis. Try to collect a sample first thing in the morning the day of your veterinarian visit.

A history of symptoms will be noted. A complete physical examination can detect an obstructed bladder and/or abdominal pain. The definitive diagnosis of kidney stones is made using abdominal x-ray or ultrasound.

If you are not able to collect a sample of urine from home, the veterinarian can collect one at the clinic. A urinalysis can detect the presence of blood in the urine, abnormal pH and the presence of crystals. A guess as to the type of stone can be made based on microscopic observation of urine, however detecting the true makeup is through submission of a stone or stone fragment to the laboratory for analysis.

Method of treatment will depend on the size, type and location of the stones.

Medications

Medications or supplements can be prescribed to acidify the urine and aid in dissolving the stones. Medications may be prescribed to increase water intake in an attempt to dilute mineral salts in the urine. Antibiotics may be required to prevent urinary tract infection or treat a current infection. Pain medications may be prescribed.

Dietary Adjustment

When risk of urinary tract obstruction is low, and depending on makeup of stones, a specialized diet may be prescribed to increase thirst (dilute the urine) or bring the pH of the urine to a normal level. These diets are normally low in protein, phosphorus and magnesium. A proper diet can result in stone dissolution within 2-12 weeks, in some situations.

Urohydropropulsion

When the risk of urinary tract obstruction is high (or the pet is already obstructed), and the stones are relatively small, urohydropropulsion may be performed. Under general anesthesia or heavy sedation, a urinary catheter is passed through the urethra and the stones are flushed out with a sterile saline solution.

Surgery

When the risk of urinary tract obstruction is high (or the pet is already obstructed), and the stones are too large for urohydropropulsion, surgery may be required. Surgery may also be necessary if dietary changes are not resolving the stones. Surgery may involve removing a kidney or cleaning stones from the bladder and flushing the bladder and urethra.

ESWL

Extracorporeal shock wave lithotripsy has the advantage of removing stones without invasive surgery. High-energy sound waves break up the stones into small enough pieces to be flushed from the urinary tract.

Follow up appointments for urinalysis and/or abdominal x-rays should be done every 4-6 weeks after treatment initiation to ensure stones are dissolving and new ones are not forming. Pets with recurrent kidney stone issues may need to be examined by x-ray or urinalysis every 3-6 months long-term.

A therapeutic diet may need to be fed for life depending on the stone type and predisposition to urinary tract infections and stone formation. Some urinary diets are not advised for long term use because they are not complete diets. There are other urinary maintenance diets that the pet will need to transition to once the stones are dissolved. Dietary changes are normally very effective in treating genetic predisposition to kidney stones.

Kidney stones tend to recur. Routine monitoring for symptoms of urinary tract infection and kidney stones is essential. Always treat urinary tract infections as soon as you notice symptoms.