What are bladder stones?
Also known as uroliths or calculi, bladder stones are rock-like deposits located within the urinary bladder. They are caused by concentrations of certain minerals in the urine. The most common types of bladder stones are struvite (also referred to as magnesium-ammonium-phosphate or MAP) and calcium oxalate. Other, less common bladder stones include ammonium urate, calcium-ammonium-phosphate, urate, cystine and compound (stones which contain different materials).
Bladder stones are named after their mineral formation. It is important that your veterinarian identifies which stone(s) your cat has and treats accordingly. They form due to the presence of excess quantities of certain minerals in the urine. Other contributing factors include persistently infected bladder, genetic predisposition, dietary, portosystemic shunt, urine pH.
Bladder stones run the risk of causing a potentially fatal urinary obstruction. This is a medical emergency and requires immediate veterinary attention. Symptoms of a urinary obstruction include straining to urinate, frequently visiting the litter tray, urinating in inappropriate spots, genital licking, crying. Males are at greater risk of a urinary obstruction due to their narrower urethra.
Struvite stones come in two categories, infected and sterile. Infected struvite stones are the result of bacteria which produce an enzyme that raises the urine pH, increasing the amount of ammonium and phosphate in the urine. Sterile struvite stones are generally associated with specific diets that contain high levels of magnesium.
Calcium oxalate stones are again they are the result of acidic urine. In the past, struvite stones were by far the most common type of bladder stone to affect cats. However, calcium oxalate stones are now gaining ground.
What are the symptoms of bladder stones in cats?
- Frequent urination (often only a few drops coming out at a time)
- Difficulty urinating (dysuria), sometimes cats will meow and appear to be distressed (but not always)
- Blood in urine (hematuria)
- Urinating outside the litter box
- Genital licking
How are bladder stones diagnosed in cats?
Your veterinarian will perform a complete physical examination and obtain a medical history from you. This examination will include abdominal palpitation, including the bladder. Most stones in the bladder are not palpable, however, your veterinarian may discover a full bladder as a result of obstruction.
Your veterinarian will wish to perform some tests, some of which may include;
- Urinalysis - To check for the presence of blood (hematuria), white blood cells (pyuria), bacteria (bacteriuria) and crystals (crystalluria) in the urine. This will also show the pH of the urine.
- X-Ray or ultrasound - To identify most stones. This will show the location and size of the stones.
- Intravenous Pyelogram (IVP/excretory urography): To see very small or radiolucent (transparent to x-ray) stones may require contrast radiography. This is where a contrast medium (dye) is injected into a vein. It is excreted via the kidneys and appears in the urine. This enables the technician to view the structures of the urinary tract.
- Analysis of the stones - To determine what type of stone(s) your cat has. This will help your veterinarian determine the treatment plan. Your veterinarian can only find out which "type" of bladder stones your cat has by surgical removal, or in some cases, by the passage of a small stone in the urine. This is generally only possible with female cats who have a wider urethra.
What is the treatment of bladder stones in cats?
Treatment will depend on the type of stone and may include:
- Antibiotics to treat bladder infection if there is one.
- Prescription diet. These alkalizing diets assist in dissolving the stones and alter the pH of the urine. It can take several weeks to several months for stones to be dissolved. These diets are not always completely successful and not all types of stone can be dissolved by diet.
- Urinary acidifiers may be used in conjunction with diet to assist with lowering the pH of the urine.
- Increasing water consumption. Switching the cat to a moist diet (such as canned food) which has a higher water content.
- Surgical removal of the stones. This is 100% successful and has the advantage of confirming the type of stone involved. Obviously, there are risks involved with any form of surgery, and there will be a recovery time, but surgery is the only option if a diet fails to dissolve the stones or if they are the type of stones that diet alone can't treat.
Your veterinarian will wish to follow up with you after several weeks. Further x-rays may be taken to see if the stones are dissolving (in the case of diet), or have returned.