Canine Bladder Stones: Diagnosis and Treatment

Dr. Marty Greer, DVM joins host Laura Reeves for a deep dive on bladder stones in dogs, how to diagnose and treat them. The following information is provided by Dr. Greer. Bladder stones are the quintessential “which came first, the chicken or the egg” question. By this, we mean that a dog can have a bladder symptoms that are caused by a bladder stone, or the bladder infection can cause bladder stones to form. Which then becomes a vicious cycle. There are two basic types of bladder stones – the first, struvite stones associated with a bladder infection or second, any of the following other bladder stones, caused by a metabolic disturbance that causes a stone to form in the urinary tract. How do bladder infections cause bladder stones? An undiagnosed, under-treated or recurrent bladder infection can lead to the development of struvite bladder stones. This is the most common type of bladder stone. Or another type of stone can cause irritation to the bladder which can cause a stone to form that is partly any of the types of stone below combined with a struvite stone. These form like a pearl in an oyster – the irritation of the infection or other stone type can cause a struvite coating on an existing bladder stone. Many metabolic stones are associated with a particular breed or disease condition causing minerals to deposit in the bladder, forming stones. These metabolic stones form with long term supersaturated minerals in the urine. With time, the crystals form which develop into a bladder stone. Other factors are the pH of the urine, inhibitors and promotors of stone formation, and macrocrystalline matrix. If something like suture is in the bladder, this can also allow a stone to form. Fortunately, most stones in the urinary tract are in the bladder itself, where they are accessible surgically. Stones in the kidney or ureter (tube from the kidney to the bladder) are not easily managed surgically or by physical removal. Stones that form in the bladder and pack together like sand in a funnel or slip from the bladder into the urethra (tube from the bladder to the outside of the body) cause urinary obstruction. This is a true medical emergency, more common in males that females due to the length and shape of the urethra, the tube from the bladder to the outside. Males have a design flaw – their urethra is more narrow and curved, causing a greater likelihood of urinary obstruction. On the other hand, females have a design flaw, a shorter wider urethra just below the rectum that allows bacteria to ascend into the bladder, increasing the risk that a female will have a bladder infection. That infection can often lead to the formation of struvite stones.

Symptoms

Symptoms of bladder disease can be virtually non-existent to severe. The symptoms can vary:

1. No signs or very subtle signs of discomfort or urinary accidents.
2. Signs of blood in the urine (often not noted until there is snow on the ground or when the urine is wiped up and blood is seen on a white towel), straining to urinate, frequency of urination, inappropriate urination, +/- fever, pain, and/or urinary incontinence. Dogs are rarely “sick” with a bladder infection – they eat, drink, and act normally other than increased trips outside or urinary accidents on the floor.
3. If obstructed, there will be abdominal pain, vocalizing, vomiting, dehydration, depression, heartbeat irregularities, bladder distension, in advanced cases, bladder rupture, collapse and death.
4. Blood work can show elevated BUN and creatinine, kidney values if obstructed.
5. Blood work may show elevated calcium if calcium oxalate stones are present.
6. Blood work may show liver dysfunction in patients with urate stones.

Below is a table showing the different types of bladder stones, comparing the composition, cause, prevention and treatment options.

Type of stone	Cause	Prevention	Treatment
Struvite or magnesium ammonium phosphate hexahydrate. Usually located in bladder but can be in renal pelvis. This is the most common stone in dogs at an incidence of  53%.	More common in female than male dogs, usually young dogs. Frequently multiple. Secondary to undermanaged bacterial bladder infection incl most commonly Staphylococcus spp., but less commonly seen urease-producing bacteria include Proteus spp. or Enterococcus spp. Rarely Escherichia coli, Pseudomonas spp., Klebsiellaspp., Corynebacterium urealyticum, or Ureaplasma/Mycoplasma spp.  May have a genetic component. Breeds: American cocker spaniel Bernese Mountain dog Bichon frise Dachshund Golden retriever Lhasa apso Miniature poodle Miniature schnauzer Pekingese Poodle Rottweiler Saint Bernard Shih tzu	1. Find and manage cause of recurrent bacterial bladder infection. 2. Preventive diets lower in protein, phosphorus and magnesium including: Royal Canin® Veterinary Diet Urinary SO, Hill’s Prescription Diet c/d™, Hill’s Prescription Diet w/d™, and Purina Pro Plan Veterinary Diets UR Urinary St/Ox. 3. Increased water intake 4. Weekly monitoring of urine pH and intervention if pH rises. 5. Periodic imaging for early detection of recurrence.	1. Dissolution diet combined with appropriate long-term antibiotics. May be dissolved medically unless obstructed. 2. Acidifiers such as D,L-methionine combined with appropriate long-term antibiotics. 3. Surgical removal or Cystoscopic retrieval 4. Physical removal.
Calcium oxalate or calcium oxalate combined stones. Usually in the bladder but can be in the renal pelvis. 2nd most common bladder stone seen in dogs.	More common in males, middle aged. Patients who have increased urinary excretion of calcium /or oxalate. May include Cushing’s disease, primary hyperparathyroidism, or cancer causing elevated calcium levels. Obesity. Steroid administration. Genetic predisposition. Bichon frise Cairn terrier Chihuahua Lhasa apso Maltese Miniature poodle Miniature schnauzer Pomeranian Shih tzu Yorkshire terrier	Calcium oxalate uroliths recur 8-9% after 6 months, 35-36% after one year, and approximately 50% after 3 years. 1.Diet Royal Canin® Veterinary Diet Urinary S/O Lower Urinary Tract Support, Purina Pro Plan Veterinary Diets UR Urinary St/Ox™, Hill’s Prescription Diet w/d™, and Hill’s Prescription Diet u/d™. 2.Potassium citrate orally. 3.Thiazide diuretics. 4.Vitamin B6	There is no known way to dissolve this stone type so must be physically removed.
Cystine	More common in males, young to middle aged. Occurs secondary to cystinuria, which is caused by increased levels of cystine excreted into urine. Uncommon. Inherited mutation of SLC3A1 gene, which leads to defective amino acid transport, described in the Newfoundland, Labrador retriever, and in the cat. Missense mutation in SLC7A9 is another cause of cystinuria in the dog. Androgen-dependent cystinuria has been described in dogs. Genetic Test: DNA testing for genetic traits is available at vetGen, Penn Gen, Paw Print Genetics, DDC, Animal Genetics, and UC Davis Veterinary Genetics Laboratory in the USA, as well as Animal Genetics-UK, Laboklin, and Animal DNA Diagnostics in Europe. Breeds: American pit bull terrier Australian cattle dog Bullmastiff Chihuahua Dachshund English bulldog French bulldog Labrador retriever Landseer Mastiff, English Miniature pinscher Newfoundland Rottweiler Scottish terrier South African boerboel Staffordshire terrier, American/bull	1. Feed protein-restricted, low-sodium diet. 2. Potassium citrate to maintain alkaline urine. 3. Some patients may also require 2-MPG therapy. 4. Do not breed affected dogs, their parents, or any other offspring. 5. For breeds with androgen-dependent cystinuria, castration can help in controlling cystinuria.	1. Low protein, low sodium, alkalizing diet: Hill’s Prescription Diet u/d™ and Royal Canin® Veterinary Diet UC Low Purine 2. Potassium citrate to alkalinize urine with a pH goal of 7.2 to 7.5 and dilute urine. 3.Physical removal.
Xanthine incidence  0.5 to 1% incidence of bladder stones in dogs	An uncommon type of purine urolith. Adults 2 to 6 years of age.  No sex predilection. Causes: Allopurinol administration Diet Idiopathic, unknown Genetic, hereditary: Cavalier King Charles spaniel Dachshund English cocker spaniel Manchester terrier	Purine-restricted, alkalinizing, diuretic diet helps prevent xanthine recurrence including renal failure diets or ultra-low protein diets with low purine levels (Hill’s Prescription Diet u/d™ or Royal Canin® Veterinary Diet Vegetarian) may help.  Add water to food to keep urine dilute. Use potassium citrate may be needed to keep urine pH alkaline.	Will not dissolve. Must be physically removed.   Stop allopurinol treatment if possible.
Silica incidence 0.9% of canine bladder stones	Incidence world-wide seems regional. Primarily male dogs. Usually 6 to 8 years of age. May be genetic with German Shepherds, Labradors, Golden Retrievers and Old English Sheepdogs being over-represented. Cause unknown.	Monitor with urine testing and imaging to check for recurrence. May help to feed more animal protein and less vegetable protein to reduce recurrence. Feeding diets higher in animal protein and lower in plant-based proteins (such as soybean, rice, corn gluten feed, oat-based cereals) may be beneficial. Increasing water intake may help decrease silica concentration in urine. Do not allow patients to eat grasses and soils with higher silica content.	No dissolution therapy known. Must be physically removed.
Calcium phosphate - incidence 1 to 2% of canine bladder stones	Brushite more common in males. Breeds predisposed include Shih tzu Lhasa apso Miniature Schnauzer Yorkshire terrier Miniature poodle Pomeranian Bichon frise American Cocker Spaniel	Identify and treat the underlying cause such as primary hyperparathyroidism or Cushing’s diease (hyperadrenocorticism). Keeping urine pH of 6.5-7.5 and urine dilute helps reduce risk of recurrence. Ideal preventive diet is unknown; diets aimed at preventing calcium oxalate uroliths are reasonable options.	Associated with primary hyperparathyroidism or Cushing’s disease (hyperadrenocorticism). These also may occur as part of stones that are largely composed of struvite or calcium oxalate. Associated with alkaline pH.
Urate incidence 5 to 8% of canine bladder stones	Either sex, usually young dogs. Uric acid and its various salts. Associated with liver disease, hepatic dysfunction, portosystemic shunts, inherited, or less commonly, caused by urinary tract infections (UTI) with urease-producing bacteria. Genetic mutation in the SLC2A9 gene: Australian shepherd Black Russian terrier Dalmatian English bulldog Miniature schnauzer New Zealand huntaway Parson Russell terrier Shih tzu Spanish water dog Yorkshire terrier	Frequently recurrent at rates of 33 to 50%. Annual or biannual imaging with ultrasound or x-rays to monitor.	1. Dietary therapy with low purine diets (eggs, dairy and vegetable protein) - may be dissolved medically unless obstructed:  Hill’s Prescription Diet u/d™, Royal Canin® Veterinary Diet Canine Vegetarian, and Royal Canin® Veterinary Diet Urinary UC Low Purine. 2. Potassium citrate at 50-150 mg/kg PO q 12 hrs or sodium bicarbonate at 25-50 mg/kg PO q 12 hrs may be used. Avoid pH above 7.5 3. Allopurinol 4. Physical removal 5. Managing underlying liver disease.
Combination stones	Any combination of the above stones can occur. The largest % component is reported when there are several mineral components to the stone.	Based on analysis	Based on analysis
Dried solidified blood	Cats only

The above table is a summary of information published on www.veterinaryinformationnetwork.com. Thanks to this author Kari Rothrock DVM.

Diagnosis

1. Symptoms are noted.
2. Urinalysis: crystals seen on microscopic evaluation of the urine, bacteria, white blood cells, and white blood cells seen under the microscope.
3. Culture – to identify the causative bacteria.
4. X-rays – seeing stones in the bladder, kidney, ureter or urethra. May require contrast x-rays.
5. Ultrasound – stones or gritty material seen blocking the ultrasound beam on ultrasound. This may be described as a “snow globe”.
6. Stone analysis – essential to know the cause and how to try to prevent formation of future stones.
7. Cystoscopy – when an endoscope is passed into the bladder to look for stones. Removal may be achieved at this procedure.

Physical Removal of stones: there are several techniques available to remove stones from the urinary tract.

1. Surgical removal – is a procedure available at most small animal veterinary clinics with basic surgical availability. If an obstruction is present, immediate surgical intervention is essential.
2. Cystoscopic retrieval – requires an endoscope and special baskets to retrieve stones from the urethra and/or bladder.
3. Voiding urohydropropulsion - With sedation or anesthesia, the bladder is catheterized, filled with fluids multiple times, and with pressure on the bladder, efforts to push the stones out through the urethra is attempted. This works best in small dogs with small stones.
4. Extracorporeal Shock Wave Lithotripsy (ESWL) - This involves using a shock wave to a patient immersed in a water bath. Bladder stones may move too much for this to have a successful outcome so is better suited for stones in the kidney or ureter.
5. Laser lithotripsy - This involves using a laser to fragment them, then the fragments are removed. This works better in female than male dogs. Small dogs and large bladder stones may not lend themselves to this treatment option.
6. Retrograde Urohydropropulsion (RU) – this involves flushing stones from the urethra back into the bladder for removal. In general, the patient will require sedation or anesthesia, followed by removal of some urine to relieve the pressure on the bladder.

Other than surgical removal, the others are usually only available at larger referral centers or veterinary schools. Dissolution – is a process by which bladder or kidney stones can be dissolved using special diets, drugs, and or antibiotics. Not all stone types will dissolve. And not all dissolvable stones will dissolve safely. If the dog has an obstruction and cannot urinate, immediate physical removal of the stones is essential as urinary obstructions are life-threatening. Not all dogs will eat the diet required to dissolve the stones. Not all owners are willing or able to administer the medications and diets necessary to dissolve the stones. Frequent monitoring of the size and location of the stone is essential to safely allow stones to dissolve. The required diets are prescription diets, and the medications are also prescription drugs. Care in selecting the correct food and medication is required, thus the reason for prescriptions from the pet’s veterinarian. Prevention can often be successful. Again, this requires that the owner(s) of the dog take great care to provide plenty of fresh water frequently, let the dog out to urinate frequently, and administer medication and food without “cheating”. Owners may also need to check weekly urine samples to assess the urine pH for early adjustments in medication and food to prevent recurrences. As a result, a mutual treatment plan with the pet owners and their veterinary team is essential for a successful outcome.