Urolithiasis (stones in the urinary tract) in Cats
Dr. Debra Primovic
Veterinary care should include diagnostic tests and subsequent treatment recommendations. A complete medical history. This should be obtained along with a thorough physical examination performed by your veterinarian. Special attention should be paid to palpation of the abdomen (to evaluate for the presence of bladder stones).
Certain diagnostic tests must be performed to confirm the diagnosis of urolithiasis and exclude other diseases that may cause similar symptoms. Tests may include:
Urinalysis. This test evaluates for urine pH, urine concentration and the presence of white blood cells, red blood cells, bacteria and crystals. The presence of crystals in the urine does not necessarily imply the presence of urolithiasis. Crystals can be seen in both normal pets and those with urolithiasis. Ideally, urine samples are collected by cystocentesis, which involves placing a needle through the abdominal wall into the bladder. The procedure of cystocentesis avoids genital or urethral contamination of the urine.
Bacterial culture of the urine. This test is used to identify urinary tract infection that may occur in pets with urolithiasis. Susceptibility testing of the urine will determine the most effective antibiotic for treatment of the infection.
Abdominal X-rays. This test is used to identify uroliths that are dense enough to be observed on plain X-rays. Some calculi cannot be seen on plain X-rays and contrast dye studies may be required.
Your veterinarian may recommend additional diagnostic tests to exclude other conditions, and to better understand the impact of urolithiasis on your pet. These tests ensure optimal medical care and are selected on a case-by-case basis. Examples include:
Complete blood count and serum biochemistry tests to evaluate the general health of your cat, evaluate kidney function, and assure that your cat can be safely anesthetized for surgical procedures to remove stones.
Ultrasound examination, which is an imaging technique in which internal organs visualized by means of ultrasonic waves directed into the tissues, and helps to identify obstruction of the urinary tract and stones that may not have been observed on X-ray studies.
Contrast dye studies to evaluate for stones not dense enough to be visible on plain X-rays. These studies are called positive contrast studies if contrast dyes are used (dye appears white on X-rays), negative contrast studies if air is used (air appears black on X-rays), and double contrast studies is which both contrast dye and air are used.
Urethrocystoscopy during which a rigid or flexible scope is passed into the urethra and bladder for direct visualization of stones or other abnormalities with the possibility of biopsy of the bladder wall.
A contrast dye study called intravenous pyelography or excretory urography can be used to evaluate the urinary tract for obstruction or the presence of stones insufficiently dense to be seen on plain X-rays.
Analysis of prostate gland fluid to evaluate for prostate infection.
Urolith analysis should be performed on retrieved stones to evaluate their mineral composition. This procedure is very important because it helps determine proper treatment and preventative therapy.
Liver function tests may be indicated for pets with a specific type of stone (ammonium urate) because these stones often are associated with congenital liver defects (called portosystemic shunts) or other liver disorders.
Treatment of urolithiasis must be individualized based on the severity of the condition and other factors that must be evaluated by your veterinarian. Treatment may include one or more of the following:
If urinary tract obstruction is present, emergency treatment is required to reestablish urine flow. Relief of obstruction may be accomplished by passage of a well-lubricated urinary catheter or emergency surgery in difficult cases.
Stones may be eliminated surgically or medically depending upon the mineral composition of the stone. There are advantages and disadvantages to both methods. The proper approach will be determined based on your pet's general health, type of stone present, location and number of stones and other factors that your veterinarian will discuss with you.
Ideally, a stone is obtained for analysis to determine its mineral composition and to decide between medical and surgical therapy. Only some stone types can be treated (dissolved) by medical means. Stones that have been passed in the urine can be submitted for analysis or small stones can be obtained by a technique called urohydropropulsion that is performed under general anesthesia. Small stones can be retrieved from the bladder using a technique called catheter-assisted urolith retrieval, which can be performed under sedation.
Surgery is the most direct and efficient way to remove uroliths, relieve obstruction and obtain uroliths for analysis. Dehydration and electrolyte disturbances should be corrected before anesthesia and surgery.
Techniques to dissolve calculi have been developed for some types of stones, such as those composed of struvite (the most common stone type), urate and cystine. An effective dissolution protocol has not been developed for oxalate uroliths, the second most common stone type. Medical dissolution consists of a combination of adjusting urine pH, eradicating bacterial infection, diluting urine and trying to reduce the urinary excretion of minerals found in the calculi. This approach often consists of a special diet and antibiotics to treat bacterial infection.
Dissolution of stones can take several months. Medical dissolution carries with it the risk of urinary obstruction because bladder stones may become small enough to lodge in the urethra as they dissolve and kidney stones can become small enough to lodge in the ureters as they dissolve. Your veterinarian may recommend adding salt to your pet's diet to increase urine production and decrease the concentration of the urine. This approach typically is used for pets with struvite and urate stones but not for those with oxalate or cystine stones. Medical dissolution of stones is not recommenced for patients with heart disease, hypertension, kidney failure or those at risk for obstruction.
A 2 to 3 week course of antibiotics is typically used to treat bacterial urinary tract infection in pets with urolithiasis. Ideally, antibiotic choice is based on bacterial culture and susceptibility testing.