Bladder Stones or Urolithiasis

Cardigan Welsh Corgi Breed Column

Our guest columnist is Barbara S. Merickel, DVM. Barbara is chair of the Cardigan Welsh Corgi Club of America Health Committee and a current board member.

Urinary calculi, uroliths, and bladder stones are all names for a medical condition known as urolithiasis Urolithiasis can occur in any dog and is not uncommon. It develops when minerals present in the urine form crystals, which then unite into small grains. Over time these grow, as more mineral is deposited on each grain.

Uroliths can develop in the kidneys, ureters, bladder, or urethra; in dogs, the majority form in the bladder.

Signs of urolithiasis include frequent urination, straining to urinate, and blood in the urine. Occasionally a small stone will pass into the urethra and cause an obstruction. Obstructed dogs strain to urinate but are unable to pass more than a drop at a time. This is life threatening, and if the blockage can’t be relieved by passing a urinary catheter, emergency surgery will be required.

Some uroliths can be palpated in the bladder, and the diagnosis can often be confirmed by radiographs, but some stones are radiolucent. In those cases the diagnosis is made with ultrasound.

One of the most common types of uroliths are composed of magnesium ammonium phosphate and are commonly called struvite stones. These are usually associated with bladder infections and alkaline urine, and they can often be dissolved by a special diet if the infection is successfully treated.

Another common stone is composed of calcium oxalate. It develops in acidic urine and is often associated with increased levels of calcium in the urine. Diets designed to prevent struvite stones may actually predispose dogs to developing calcium oxalate stones.

Stones composed of calcium phosphate are relatively rare in dogs. Increased levels of calcium in the blood or urine may contribute to stone development. Silica stones are very rare in dogs and may be associated with diets containing silica-rich ingredients like rice or soybean hulls.

Cystine stones develop in dogs with cystinuria, a genetic defect that allows the amino acid cysteine to pass into the urine. Although rare in the dog population overall, it has been diagnosed in the Cardigan Welsh Corgi along with many other breeds. Cystine stones can often be dissolved by a special diet; since the dog will continue to excrete cysteine, a control diet will be needed to prevent the recurrence of stones.

Genetic tests for cystinuria have been developed for Labradors and Newfoundlands but have not been validated for Cardigans.

Urate stones are composed of uric acid and its salts. They develop in dogs with liver disease, most commonly portosystemic shunts, or in dogs with hyperuricosuria, a genetic defect that prevents the conversion of uric acid to allantoin. This condition is thought to affect all Dalmatians, and it affects many other dogs as well, and there is a genetic test available for all breeds.

It is essential to know the composition of bladder stones in order to successfully treat and prevent recurrence. Any urinary stones that are removed from dogs should be tested by a laboratory that specializes in urinary calculi analysis. In most cases, dogs with cystine or urate stones should not be bred. —B.S.M.

Thank you, Barbara. —Column coordinator Jeff Welch


First published in the AKC Gazette Digital Edition, December 2015.

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