Canine Urolithiasis – Calculi Stones Blocking Dogs Urinary Tract

Description of Canine Urolithiasis

Canine Urolithiasis is a condition where excessive crystals in the urine combine to form stones, also called calculi or uroliths, which can result in blocking or partially blocking the urethra and making it difficult or impossible for a dog to pass urine. Immediate medical attention is required and, in situations of a complete blockage, death can result in a matter of a day or two if the blockage is not removed.


Sign and Symptoms of Canine Urolithiasis

The severity of the symptoms will depend on the extent of the blockage. It is important to note that you may not see all of the signs. The most obvious sign when there is a blockage will be the dog's inability to pee or difficulty in doing so where the urine is seen as dripping versus streaming.

Common signs of Canine Urolithiasis are:
Frequent urination attempts
Straining to urinate / pee
Urinating / peeing in inappropriate areas (bedding, carpet)
Urinating in drips versus in a stream
Complete failure to urinate (immediate attention is required)
Blood in urine
Particles in urine or on tip of penis
Displaying signs of pain and discomfort
Stands stiffly with arched back
Distended stomach
Bladder sensitive on palpation
Lethargic (lack of energy)
Chills; trembling
Loss of appetite
Fever; high temperature


Diagnosis of Canine Urolithiasis

Abdominal palpation
Urine culture to determine type of stone and infection
Obstruction felt with urethral catheter
Radiographic examination (xray)


Treatment of Canine Urolithiasis

When an obstruction is caused by urinary tract calculi (stones), the veterinarian will attempt to flush the stones back into the bladder. The stones will be dissolved by a prescription of a special diet and/or medication, if possible. Dissolution generally takes 8 to 12 weeks, but can take upwards of 20 weeks in some cases. If the stones are not able to be dissolved, the vet may attempt to break them up with the use of ultrasonic waves (lithotripsy).

It is important to determine the type of urolith (stone). The most common stone types are struvite, calcium oxalate, and urate. Your dog may pass small stones which can be collected. If you can get a sample and bring it to your veterinarian, the process of identifying the stone type will be much easier and therefore the path to treatment much quicker.

Struvites are more commonly seen in female dogs one to eight years of age and are more common in the following small breeds: Miniature Schnauzers, Miniature Poodles, Bichon Frise, and Cocker Spaniels.

Calcium Oxalate uroliths are primarily seen in male dogs two to ten years of age and are more common in the following dog breeds: Schnauzers, Lhasa Apsos, Yorkshire Terriers, Bichon Frise, Shih Tzus, and Miniature Poodles. Calcium Oxalates can be seen with other types of stones as well, which can be especially challenging in the treatment and future prevention of stones. Oxalate stones cannot be dissolved and must be either surgically removed or broken down with sound waves (lithotripsy).

Urate and Ammonium Urate stones are commonly found in middle aged male Dalmations, as well as English Bulldogs and Yorkshire Terriers.

It is vital to note that any breed can suffer from Canine Urolithiasis. (We have a purebred Pug that has been affected and was the inspiration behind the research for this article.)

Antibiotics will be necessary if infection is present (or in cases of surgery — see below).

Surgically removing the stones may be necessary. There are risks with dissolution as well as with surgery. For male dogs that have recurring stones or have a tumor of the penis, a prescrotal or scrotal urethrostomy may be necessary. In male dogs, there is a hollow bone in the penis referred to as the "os penis" (or Baculum) which is much like a pipe. As it is bone, it is not flexible to allow a larger stone to pass through the urethra. The urethrostomy procedures involve making an opening to the urethra which will allow the urine and stones to exit. The opening may be temporary or permanent. In cases of penile tumors, the urethrostomy is permanent and the penis is removed.

Blood work and an electrocardiogram (ECG), due to the failure to pass potassium, is also often performed to evaluate any damage. The kidneys may suffer some damage from the blockage, however this is usually temporary.


Management of Canine Urolithiasis

Your vet may ask you to monitor your dog's urine pH and/or to bring urine samples for follow-up urinalysis. The vet may also recommend regular serum chemistry profiles, ultrasounds, and/or x-rays to detect any stones while they're are still small and manageable.

Potassium citrate and vitamin B6 supplements, as well as thiazide and chlorothiazide diuretics, are often indicated for oxalate bladder stones.

It has been said that 50% of dogs will develop new calcium oxalate stones within three years of surgery. According to a study at the University of Minnesota, 42% of the canine patients with calcium oxalate uroliths had recurrences within 2 years. A special case is the Bichon Frise which has been shown to have an extremely high chance of recurrence of oxalate bladder stones, seeming to have replacements reform almost as soon as they are removed.

In any case, a change of diet is recommended and strict adherence to that diet is required. Human food and treats should be eliminated from the diet. Wet food is recommended over dry, and fresh water should always be available.


Differential Diagnoses

There are other conditions that can cause a dog to strain when urinating. Based on that symptom alone or when coupled with blood in the urine, vets will often look for bladder, kidney, or prostate disease or infection. Urinary tract infection (UTI), sometimes referred to as cystitis, is a very common problem associated with urinary issues and occurs when bacteria colonize the urinary tract. Other conditions causing a difficulty in urinating can be an enlarged prostate gland due to tumor, cyst, or high level of hormones or in dogs with perineal hernias.


Resources and Further Reading

Calcium Oxalate and Struvite Uroliths – University of Minnesota
Urethral Obstruction in Male Dogs – American College of Veterinary Surgeons (ACVS)
Oxalate Bladder Stones (Canine) By Wendy C. Brooks DVM, DABVP
Canine Urolithiasis – Merck Veterinary Manual
Canine Urolithiasis An Owner's Guide
Minnesota Urolith Center – University of Minnesota
Images: Canine Urolithiasis (Bladder Stones) Illustrations

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