Therapeutic Options for Dogs & Cats with Urinary Calculi
Kidney stones” are a common problem in both species. We use the term “urolithiasis” which means calculi (stones) anywhere along the urinary system from the kidney to the ureter, bladder and urethra. This sounds simple but actually is a complicated subject. Signs of calculi in pets: Urethral stones 1. Difficulty in passing urine or a complete inability to pass urine 2. Straining to urinate. Standing or squatting in a position as if to urinate with no results or dribbling or urine 3. Accidents in the house 4. Visible blood in the urine 5. Increased frequency of urinations 6. Signs of discomfort such as restlessness or crying, vocalizing, panting or reluctance to lie down. Bladder stones 1. Increased frequency of urination 2. Accidents in the house 3. Straining to urinate 4. Visible blood in the urine Ureteral stones 1. Sudden onset of discomfort such as restlessness, crying, vocalizing, panting and reluctant to lie down. 2. Pain on touching the abdomen near the kidneys 3. Signs of systemic illness such as vomiting or loss of appetite. 4. If stones are present in both ureters the pet may suddenly become quite ill and stop producing urine Kidney stones 1. Signs of discomfort. 2. Fever if infection is present 3. Pain on touching the abdomen near the kidneys Any of these signs should cause the owner to take their pet to the veterinarian as soon as possible or often on an emergency basis depending on the severity of the signs. If unsure of what to do, call the staff at AVS 314-739-3330 for help. Common types of stones In dogs the two most common stone types are Struvite, also called Magnesium Ammonium Phosphate, and Calcium Oxalate. Struvite calculi are usually associated with urinary tract infection in dogs. In cats, struvite calculi will occur with the syndrome of lower urinary tract disease for which the cause is not known. Calcium Oxalate stones occur in both species and their cause is generally unknown. Other stones include urates, cystine, xanthine and silica. These are much less common but can occur in certain breeds or when other metabolic diseases are present. Diagnosis of stones After taking a careful history which points the veterinarian toward the affected system, a physical examination is performed. Pets with bladder or urethra signs should always have a rectal exam performed to feel the urethra for the presence of stones or tumors. If an enlarged bladder is felt, immediate therapy is required. After the physical, a variety of tests are indicated. This includes urinalysis and urine culture. Xrays need to be taken and must include the kidneys, bladder and entire urethra. The pet often requires an enema to remove fecal material so good images are obtained. Not all stones are visible on xray (some are radiolucent) and ultrasound is the primary method of imaging. The ultrasonographer can obtain good images all the way from the kidneys to the upper urethra although the lower urethra cannot be seen with ultrasound. Therapy of stones If urinary tract infection is present, it is best treated by first obtaining a urine culture so the specific type of bacteria is known and what antibiotics are effective can be determined. Several antibiotics are “broad spectrum” and will likely work but this should not be left to chance. Infection not only must be treated but it also must be prevented from recurring. Prevention requires removing underlying causes such as stones, or anomalies of the urinary or reproductive tracts. Struvite stones will often dissolve when the infection is treated and a special stone reabsorbing diet is prescribed. Both Royal Canin and Hill’s manufacture diets of this type. Surgical or other therapies of stones The conventional method of removing stones is surgery. Techniques have been used for many years to remove stones from anywhere in the urinary tract. Some of these procedures are done by general practice veterinarians but others should be performed by a surgical specialist. Whenever stones are removed they are submitted for analysis so the type of stone is determined. This is critical for future prevention of more stones. Newer methods involving interventional radiology or endourology have recently become available at AVS. These include laser lithotripsy which means the veterinarian places a cystoscope into the urethra or bladder and uses a holmium:yag laser fiber to direct laser light directly into the stone to cause it to fragment. The fragments are then flushed out or removed with stone retrieval forceps or baskets. This is effective for urethral stones and some bladder stones. The advantage of this technique is that it does not require a surgical incision although some urethral discomfort is present for a few days afterward. Other bladder stones can be removed via percutaneous cystolithotomy (PCCL). With this technique, a small incision is made over the bladder, a threaded cannula is placed into the bladder then the stones are flushed out or the cystoscope is placed into the bladder via the cannula and used to remove the stones via grasping forceps or stone retrieval baskets. The advantage of this technique is diminished surgical trauma to the patient and better visualization of the inside of the bladder to ensure complete stone removal. Some stones can often be missed with conventional surgery. A more serious problem is present when stones are in the kidney or urethra. The technique currently employed at AVS is to place a ureteral stent which is a device that allows urine to flow via the stent from the kidney into the bladder. These are placed surgically or endoscopically depending on the situation. These can be left in place long term. Please see article about “Pogo”. In some cases, the ureter must be bypassed by a Subcutaneous Ureteral Bypass system (SUB). This device employs catheters in both the kidney and bladder with a connecting port in the subcutaneous tissue. AVS maintains a complete inventory of devices necessary for these procedures. In dogs, certain kidney stones can be treated with Extracorporeal Shock Wave Lithotripsy. In the Midwest, the patient must be referred to Purdue University College of Veterinary Medicine for this procedure.