Stones or crystals in the urinary tract are relatively common problems in cats.  Both sexes are affected.  Bloody urine and difficulty in urination are cardinal signs of bladder stones.

Types and Causes

Initiating causes of urinary stones in cats are not known.   Fifteen years ago, the most common urinary "stones" were crystals of magnesium ammonium phosphate ("struvite") in urinary tract mucus.  This produces a gritty sludge with a consistency of toothpaste.  More recently, large dense stones of calcium oxalate have become more frequent, possibly due to the use of magnesium-restricted, aciditic diets used to inhibit struvite formation.  Other types of stones are rare in cats.

Signs

Production of large amounts of struvite crystals is associated with bloody urine, difficult urination, and occasionally complete urinary tract obstruction in cats. Standing in the litter box for unusually long periods, especially with the back humped, is suggestive of lower urinary tract obstruction.  Affected cats may lick their genitals due to a burning sensation or spasms in their urinary tract.

Calcium oxalate stones may develop in the recesses of the kidneys and cause pain and sometimes obstruction as they try to pass down the ureter to the urinary bladder.  Once they develop further in the bladder, they can obtain very large size and irritate the bladder wall, or while relatively small, they may pass down the urethra and cause pain and obstruction in the penis.  Females can pass the stones through the urethra more easily than in males.

Diagnosis

Urinalysis, bacterial urine culture, x-rays, and ultrasonography may be needed to determine whether stones are the cause of signs, the type of stones, and their locations.

Treatment

Urethral obstruction is an emergency.  Toxins in the urine can be absorbed into the blood and death may occur within 48 hours.

Struvite crystal obstruction and bladder irritation can usually be treated by using urinary acidifiers to dissolve the crystals and modified diets that are magnesium-restricted.  If the struvite crystal and mucus mixture has become infected with bacteria, antibiotics are also indicated, but this is uncommon.

Calcium oxalate stones must be surgically removed from male cats.  Attempts to dissolve the stones may make them small enough to pass into the urethra and cause a total obstruction to urine flow.

Prevention Measures

Feed appropriately to prevent obesity

Consult your veterinarian on the best diet for your cat

Provide clean, fresh water at all times

Keep the litter box clean and watch your cat’s habits using the litter box

If your cat has difficulty in urination, seek immediate veterinary attention

For more information, contact your local veterinarian or the MU Veterinary Medical Teaching Hospital 573-882-7821 or visit http://www.vmth.missouri.edu/

C.B. Chastain, DVM
Professor, University of Missouri
College of Veterinary Medicine