Feline Urolithiasis (Stones in the Urinary Tract)
Urolithiasis refers to the formation of stones (calculi or uroliths) in the urinary tract. Calculi can be found anywhere in the urinary tract, in the kidneys, the ureter or the bladder, but are most common in the bladder.
Below is an overview of Urolithiasis in cats followed by in-depth detailed information on the diagnosis and treatment of this condition.
Calculi form due to oversaturation of the urine with certain minerals. Several factors may contribute to this oversaturation including increased concentrations of specific minerals in the urine, alterations in the pH (acidity or alkalinity), highly concentrated urine, presence or absence of stimulators, and inhibitors of crystal formation.
Several factors can contribute to development of urolithiasis. These include:
Genetic factors like the altered urate metabolism in Dalmatians
Differences in dietary composition and water intake
Underlying metabolic diseases such as high blood calcium concentration arising from overactivity of the parathyroid glands
Congenital problems such as abnormal blood vessel shunting blood around the liver and contributing to urate stone formation
Bacterial infections of the urinary tract (struvite stone formation). The cause for stone formation is unknown in many cases.
The various types of calculi are named according their predominant mineral composition. In cats, calculi composed of the minerals magnesium ammonium phosphate (commonly called struvite) and calcium oxalate are most common. Urate calculi occur less commonly. Cystine and silica calculi are relatively rare. The different types of calculi must be treated differently. Consequently, it is important for your veterinarian to be able to obtain calculi for chemical analysis.
The risk of recurrence for urolithiasis is high and ranges from 20 to 50 percent. The pet’s symptoms depend upon the number of stones, their location in the urinary tract, the physical characteristics of the stones (smooth or jagged), and the presence of bacterial urinary tract infection.
What to Watch For
Difficult or frequent urination
Urinating in inappropriate locations
Blood in the urine
Symptoms caused by kidney stones include back or abdominal pain or occasionally abnormal odor to the urine if bacterial infection is present. Surprisingly, however, many pets with kidney stones have few or no symptoms.
Diagnosis of Urinary Tract Stones in Cats
Diagnostic tests are needed to identify urolithiasis as the cause of your pet’s symptoms and to exclude other disease processes. Your veterinarian may recommend:
Complete medical history and physical examination, including palpation of the abdomen. Bladder stones can be difficult to palpate due to the tendency of many pets to tense their abdomen when the veterinarian attempts to palpate them. The medical history may include questions about the pet’s urine stream, the frequency of urination, presence of blood in the urine, change in water consumption, changes in appetite, weight loss and history of previous illness or infection.
Urinalysis to evaluate urine concentration, acidity or alkalinity (called pH), presence of red blood cells, white blood cells, bacteria and crystals
Abdominal X-rays to identify stones that are dense enough to be visualized
Other diagnostic tests that may be completed include:
Urine culture and sensitivity to identify bacterial urinary tract infection
Serum biochemistry tests to assess kidney function
Complete blood count to evaluate for infection
Abdominal ultrasound to evaluate for obstruction of the urinary tract by stones
Contrast dye X-ray studies to visualize some stones not visualized on plain X-rays
Stone analysis to identify the mineral composition of the stones and guide your veterinarian in treating urolithiasis
Treatment of Urinary Tract Stones in Cats
Treatments for urolithiasis may include one or more of the following:
Treatment of bacterial urinary tract infection with antibiotics
Removal of stones surgically or by dietary intervention. There are advantages and disadvantages to both methods. Surgery is invasive but usually insures removal of all stones and allows for mineral analysis of the stones. Dissolution of stones by dietary methods is not invasive but does not allow mineral analysis of the stones and requires your veterinarian to make an educated guess about the type of stone present. Some stones can be dissolved by dietary means and others cannot. Whether or not to attempt dietary dissolution will depend on your pet’s general health, the type of stone suspected, the location and number of stones and other factors that your veterinarian will discuss with you. In many instances, surgery is the most direct way to remove stones and submit them for analysis.
At home, be sure to administer any medications prescribed by your veterinarian. Give antibiotics according to the schedule prescribed. It’s important to allow your pet free access to fresh clean water.
Follow-up with your veterinarian for physical examinations and urinalysis as directed. Urine culture should be repeated 5 to 7 days after completion of antibiotic treatment to ensure eradication of infection. If your pet has a poor response to treatment, further workup may be required to search for underlying disease processes.
Stone analysis will guide your veterinarian’s treatment plan:
Struvite stones: antibiotics to treat bacterial infection
Oxalate stones: thiazide diuretics and potassium citrate
Urate stones: allopurinol
Cystine stones: penicillamine or 2-mercaptopropionyl glycine (2-MPG or Thiola)
Most stones are difficult to prevent. Providing your pet with frequent opportunities to urinate and an ample supply of fresh clean water may help.
Prompt treatment of urinary tract infections can help reduce the potential for certain stone formation.
In-depth Information on Urolithiasis in Cats
Other medical problems can cause symptoms similar to those encountered in cats with urolithiasis. Your veterinarian will exclude these conditions as necessary before establishing a diagnosis of urolithiasis.
Clotting disorder (diagnosed with platelet count and tests of blood coagulation)
Congenital defects (those present at birth) such as ectopic ureters
Bacterial cystitis (lower urinary tract infection)
Drug-induced cystitis such as that caused by cyclophosphamide, which is a drug used to treat some types of cancer and immune diseases
Hydronephrosis, which is distension of the urinary space within the kidney due to obstruction
Cancer of the urinary tract
Disorders of the nervous system that interfere with urination
Rare parasites of the urinary tract (kidney and bladder worm)
Diseases of the prostate gland
Veterinary care should include diagnostic tests and subsequent treatment recommendations.
Certain diagnostic tests must be performed to confirm the diagnosis of urolithiasis and exclude other diseases that may cause similar symptoms. Tests may include:
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).
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.
Follow-up Care for Cats with Urinary Tract Stones
Optimal treatment for your pet requires a combination of home and professional veterinary care. Follow-up with your veterinarian is essential. Administer any antibiotics prescribed by your veterinarian and allow your pet free access to fresh clean water.
If your pet has had surgical removal of calculi, monitor the incision site for redness, swelling or discharge. Do not allow your pet to lick at the suture area. An Elizabethan collar can be used for pets that tend to lick their incisions. Call your veterinarian if you have questions or problems.
Follow-up with your veterinarian for physical examinations and urinalysis. Bacterial culture of the urine should be repeated 5 to 7 days after completion of the antibiotic course to ensue eradication of infection. Periodic urinalyses are recommended every several months to monitor for development of new bacterial urinary tract infections.