Uroliths are rock-like stones found within the urinary tract causing irritation and secondary infection. Struvite (also referred to as magnesium ammonium phosphate or MAP) account for approximately 65% of stones, 20% are calcium oxalate , other stones include calcium phosphate, ammonium urate, silica, and cystine. The stones are named after their mineral formation and are caused by varying reasons. It is important that your veterinarian identifies which stone(s) your cat has and treats accordingly.
Crystals develop and combine to form stones over time. They are composed of a small amount of organic matrix, composed of mucoprotein, surrounded by layers of polycrystalline (many crystals) concretions.
Urinary stones can lead to inflammation of the urinary tract, which may lead to urinary tract infection , or they can cause a urethral blockage, especially in male cats, leading to urinary obstruction. Blockage leads to uremic poisoning and hyperkalemia (high blood potassium). This is a life-threatening situation and veterinary assistance must be sought immediately.
What are the symptoms of urolithiasis in cats?
The underlying feature of urolithiasis is difficulty passing urine. Symptoms include:
Frequent urination (pollakiuria), only passing small amounts of urine.
If you notice any of the above symptoms, immediate veterinary attention is required as a cat who develops a full urinary blockage lead to a dangerous build-up of toxins in the bloodstream (uremia), which is life-threatening.
How are uroliths diagnosed?
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 uroliths 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 uroliths. This will show the location and size of the uroliths.
Intravenous Pyelogram (IVP/excretory urography) – To see very small or radiolucent (transparent to x-ray) uroliths 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.
Microscopic analysis of the stones – To determine what type of stone(s) your cat has. This will help your veterinarian determine the treatment plan.
How is urolithiasis treated at home?
Treatment depends on the cause and severity of the condition. Treatment will also vary according to the type of crystals your cat has.
As stone build up is caused by urine which is too concentrated it is important to try and get more fluids into your cat, to reduce the concentration of the urine. It is also beneficial to aim for a pH below 6.5. pH in a cat’s urine usually ranges from 5.5 to 8.0, but diets which result in < 6.5 decreases the chances of struvite crystals forming.
Diet: Moisten dry food or change to canned/raw food. Cats are designed to obtain most of their water through the food they eat. Dry food contains approximately 10% water, whereas canned or raw food contains approximately 70% water and most cats don’t compensate by drinking more water. Avoid fish flavoured food. Feed a diet which increases the acidity of urine. There are special diets which are created to increase thirst.
Stone dissolving diets may be recommended. These are restricted in magnesium and acidifying. Stone dissolving diets only work with struvite stones. Unfortunately, long-term use of an acidifying does carry some risks, one of which is the increased chances of developing calcium oxalate urolithiasis.
Increase water consumption: Encourage drinking by other means, such as providing a drinking fountain for your cat.
Antibiotics: This form of treatment is used for mild cases of urolithiasis. The decision to prescribe antibiotics to a cat who is affected by urolithiasis depends on upon the severity of the case.
How is urolithiasis treated a the vet?
Urine: If your cat is completely blocked then your veterinarian may extract urine by placing a syringe through the abdomen and directly into the bladder and draw out the urine. This is a fast and effective way of emptying out the bladder in an emergency situation. Alternatively, he may choose to catheterise the cat immediately. See below for info on catheterisation.
Catheterisation: This is the system by which a catheterisation needle is inserted into what is called the Cephalic vein. This vein is located in one of the front legs of the cat. After the intravenous needle is placed in the front leg of the cat it is wrapped. A urinary catheter is also placed in the cat’s urethra. This helps re-hydrate the affected cat and also helps flush out small uroliths. Catheterisation on a cat takes place while the cat is under anaesthesia.
Surgical removal of uroliths: The advantage of surgical removal is that the stones are completely removed and can be identified. However, as with any surgery, there are also risks.
Voiding urohydropropulsion – The bladder is flushed with a sterile liquid to void it of stones.
Retrograde urohydropropulsion: Stones trapped in the urethra are flushed back into the bladder using a sterile liquid.
Perineal urethrostomy: This surgery involves partial amputation of the penis to the point where the urethral opening is larger. This will help reduce the risks of blocking, although it is still possible a small number of cats will become blocked even after the perineal urethrostomy.
Fluid Therapy: This form of therapy is often used before catheterisation is attempted. It involves the feeding of fluids to the cat in order to continue to flush out the cat’s urinary system (particularly the bladder).
 The Feline Patient – Gary D. Norsworthy, Mitchell A. Crystal, Sharon K. Fooshee and Larry P. Tilley.