Urolithiasis (stones)

What is ... ?: 

Urolithiasis is a condition in which crystals in the urine combine to form stones, also called calculi or uroliths. These can be found anywhere in the urinary tract, where they cause irritation and secondary infection. Most end up in the bladder or in the urethra, where they may cause obstruction, which is a medical emergency. Several different types of uroliths have been identified, with struvite stones (magnesium ammonium phosphate) the most common. Dogs of any breed can develop uroliths, but a genetic predisposition to producing crystals in some breeds makes the development of stones more likely.

Dalmatians have a defect in the pathway (purine metabolism) that normally leads to the breakdown of urates, a by-product of protein digestion. This results in increased urate excretion in the urine, and this predisposes them to the formation of urate crystals and eventually, stones. In some other breeds, an inherited defect in a different pathway causes excessive urinary excretion of the amino acid cystine, resulting in cystine crystals and potentially stones in the urine.

 

Type of crystal/stone Breeds affected Inheritance Treatment Prevention
Struvite (triple phosphate, MAP) Bichon frise, Dandie Dinmont terrier, miniature poodle, miniature schnauzer,  shih tzu, Yorkshire terrier, seen in many other breeds as well This is the most common type of stone seen, but little is known about inheritance. Dissolve medically or remove surgically; treat UTI*
 Feed special diet; acidify urine
Urate/biurate

Dalmatian

Black Russian terrier, dachshund, English bulldog,  giant schnauzer, large Munsterlander, mastiff, Parson (Jack) Russell terrier, South African Boerboel, Weimaraner

Autosomal recessive Dissolve medically or remove surgically Special diet (reduced purine) and, if necessary, allopurinol; alkalinize urine
Calcium oxalate Bichon frise, Dandie Dinmont terrier, Lhasa apso, miniature poodle, miniature schnauzer, Shih tzu, Yorkshire terrier  Little is known Remove surgically. Special diet; alkalinize urine.
Cystine Dachshund, English bulldog, Newfoundland, Irish terrier, mastiff

Thought to be autosomal recessive 

  Special diet; alkalinize the urine.
Xanthine Cavalier King Charles spaniel, dachshund
 Thought to be autosomal recessive    

* UTI - urinary tract infection

For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have listed breeds for which there is a consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.

How is ... inherited?: 

The trait for hyperuricosuria (elevated uric acid in the urine, leading to urate stones) is autosomal recessive. It is present in all Dalmatians, although not all will develop urolithiasis. A DNA test is available (see here) to test for this mutation in the many breeds affected. There is also a test available for the trait causing high cystine in the urine (cystinuria) of Newfoundland dogs.

What does ... mean to your dog & you?: 

The changes in the urine are generally present from birth. However it usually takes some time for crystals to form and combine into stones that cause problems, most often between 3 and 6 years of age. The signs you will see in your dog depend on where in the urinary tract the stones end up. They collect most commonly in the bladder, in which case you may see blood in the urine, difficulty and pain in urinating, and small frequent amounts of urine.
 
Urinary tract obstruction is a serious condition that occurs when a stone completely blocks the urethra and thus blocks the outflow of urine (more common in male dogs, who have a smaller urethra). Signs include straining to urinate, vomiting and loss of appetite, weakness and lethargy (due to toxins building up in the body).

How is ... diagnosed?: 

If your dog is showing the physical signs described above, your veterinarian will do an analysis of his/her urine (urinalysis) to look for crystals and also for a bacterial infection, which is commonly seen with this condition. Many stones can be seen with x-rays; some (especially urate uroliths) will only show up with contrast radiography.  Ultrasound can generally detect stones of all types.
FOR THE VETERINARIAN
Types of uroliths vary in radiodensity. Struvite and calcium oxalate uroliths are usually obvious on radiography; urate uroliths may be radiolucent and therefore require contrast radiography or ultrasonography.
 

How is ... treated?: 

A combination approach is usually needed. Stones are often small and numerous. Larger ones may be removed surgically - this is necessary if the stone is blocking the ureter or a kidney, if your dog is in pain, or if the stones do not dissolve after a period of medical management. The medical approach is to dissolve the stones gradually by changing the pH of the urine, ie. making it more or less acidic (depending on the type of stone) through medication and changes in diet.Special diets also result in a larger volume of more dilute urine, making it easier for a dog to pass the stones. Your veterinarian will monitor your dog's progress through periodic radiographs and analysis of the urine over the period of time the stones are dissolving (which can take some months). Some types of stones are more amenable to dissolution than others.
 
In all cases of urolithiasis, in addition to paying careful attention to your dog's diet, you can help to reduce the formation of stones by providing lots of fresh water and regular opportunities to urinate, so that urine doesn't accumulate in the bladder allowing time for stones to form. You can increase your dog's water consumption by feeding a canned diet with a high water content, or mixing dry food with water.
 
Bacterial urinary tract infections are common with urolithiasis, and should be treated promptly.

Breeding advice: 

Affected animals should not be bred, and it is preferable to avoid breeding their parents and siblings as well. Carriers for hyperuricosuria, and for cystinuria in the Newfoundland, can be identified through DNA testing (see links below).
 
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources: 

Faunt KK, Cohn LA. Urolithiasis (Oxalate, Struvite, Urate/Biurate, Other). In: Côté E, ed. Clinical Veterinary Advisor Dogs and Cats. Missouri: Mosby Elsevier, 2007:1125-1132.
 
Karmi N et al. Estimated frequency of the canine hyperuricosuria mutation in different dog breeds.J Vet Intern Med. 2010, 24:1337-1342.
 
Sargan DR. Urolithiasis. In IDID - Inherited diseases in dogs:web-based information for canine inherited disease genetics. 2002-2011.
 
Veterinary Genetics Laboratory - DNA test for hyperuricosuria
 
Optigen - DNA test for cystinuria in Newfoundland dog

 


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