Reviewed and fact checked by Bruce Whittle, DVM
Urolithiasis means calcified “stones” of varying sizes that form in the urinary tract – the kidneys, bladder or urethra. Bladder stones are the most common and can vary from a sand-like sediment to “stones” that can be over 2 inches in diameter! There are multiple types of stones that can form depending upon the dog’s breed and diet.
What are the Different Types of Urinary Stones in Dogs?
1) Struvite stones (Magnesium-ammonium-phosphate)
-
The most common type of bladder stone.
-
Miniature Schnauzers, Miniature Poodles, Bichon Frise and Cocker Spaniels seem to be more likely to develop this type of stone.
-
Usually result from a bacterial infection of the bladder which is more common in females than in male dogs due to the shorter length of their urethra.
-
Affected dogs can be fed a special diet to either prevent stone formation or can sometimes dissolve the stones and prevent the need for surgical removal.
2) Calcium oxalate
-
Second most common type or urinary stone.
-
Miniature and Standard Schnauzers, Miniature Poodles, Lhasa Apso, Shih Tzu, Yorkshire Terriers and Bichon Frise seem to be more predisposed to this type of stone, possibly due to a genetic predisposition—genetic testing may be available.
-
Affected dogs have a defect in a substance called nephrocalcin, that usually inhibits the formation of calcium oxalate stones in normal dogs.
-
This condition is more common in middle-aged to older male dogs.
-
Unfortunately, calcium oxalate stones cannot be dissolved via feeding a special diet and some type of physical removal of the stones is necessary.
3) Urate stones
-
Most commonly found in Dalmatians but also in Bulldogs, Black Russian Terriers, American Pit Bull Terriers and American Staffordshire Terriers.
-
Genetic mutation prevents these dogs from converting uric acid into allantoin—a genetic test is available to identify this mutation.
-
Uric acid thus builds up in the body, gets into the urine and crystallizes into urate stones.
-
Special diets are available that may dissolve the urate stones.
4) Cystine stones
-
Caused by increased excretion of cystine in the urine as a result of a metabolic problem that affects the kidneys.
-
Often due to a genetic mutation in dog breeds including Newfoundlands, Labrador Retrievers, Scottish Terriers, Australian Cattle Dogs, Miniature Pinschers, Mastiffs, English Bulldogs and French Bulldogs – genetic testing is available.
-
Male dogs are most commonly affected, usually before 2 years of age.
-
Neutering can result in greatly decreased cystine levels thus lowering risk of stone formation.
-
Cystine stones do not show up very well on radiographs but can be diagnosed with ultrasound and by finding characteristic cystine crystals in a urine sample.
5) Silicate stones
-
Silicate stones are the least common type of urinary stone.
-
Stones often have a characteristic spiny shape, although other types of stones can occasionally look similar.
-
Most commonly seen in male dogs.
-
German Shepherds, Shih Tzus, Old English Sheepdogs, Labrador Retrievers, and Golden Retrievers appear to have a higher risk of developing these stones.
-
These stones cannot be dissolved through dietary changes, and some form of surgical removal is necessary.
-
Silicate stones seem to have increased in prevalence due to an increase in the amount of plant proteins incorporated in dog foods.
-
Prevention: feeding a diet lower in plant-based nutrients and increasing water intake, often by feeding a canned diet or soaking dry food to absorb moisture can be helpful.
What are the clinical signs of urinary stones? (How will I know to suspect them in my dog?)
-
Frequent urination of small amounts, often with straining.
-
Blood in the urine.
-
“Potty accidents” in the house.
How will my veterinarian diagnose if my dog has urinary stones?
-
Microscope exam of urine sample to look for crystals.
-
Chemical exam of urine for acidity, protein, blood and specific gravity (how dilute is the urine?)
-
Radiographs (except cystine stones which are less dense)
-
Ultrasound.
If my dog has urinary stones, how can we treat them and then prevent future episodes?
-
Special diets can be fed that may dissolve the stones or prevent future stones.
-
If stones are present in the urethra, placing a urinary catheter and pulsing liquid through it may dislodge the stones and push them back into the bladder.
-
Surgery may be required to remove stones from either the kidney, bladder or urethra, especially with larger stones.
-
Endoscopy can be used through the urethra or laparoscopically through the abdominal wall (similar to gallbladder surgery in people) to remove smaller stones.
-
If a urinary blockage has been present for a few days, the dog’s metabolic status will be worsened making anesthesia and surgery more risky.
Summary
-
The key to successful treatment of urinary stones is early diagnosis.
-
Contact your dog’s veterinarian when you see signs of urinary stones as previously described: blood in the urine, consistent straining without voiding urine or uncharacteristic potty accidents.
-
Most urinary stones are not life-threatening unless their treatment is delayed.
-
Urinary stones are not uncommon and dogs of predisposed breeds should be monitored closely.
As a dog owner who knows what to watch for you will be able to present your dog to your veterinarian in a timely manner to achieve the best outcome.
