Struvite Urolithiasis in Dogs

Just as we humans can experience urinary system problems, so can our animal companions.  Urea is the by-product of the biochemical process of protein metabolism (ammonia). Any excess of ammonia is released into the bloodstream by the liver, then filtered by the kidneys and finally excreted from the body in the urine flow.  As the body digests what the dog eats, various minerals are isolated for use by the body or for removal from the body.  Magnesium, ammonia and phosphate are all common elements found in urine.  

When these elements are in high enough concentrations, a binding takes place and crystals or uroliths are formed.  These uroliths are irritating and can inflame the bladder tissues.  This irritation and inflammation can cause mucous formation which can create an environment that allows the crystals or uroliths to fuse together to form the struvite stones. As these stones then travel through the urinary system, various symptoms can be experienced by the dog and the possibility of obstruction, either partial or complete, exists.

Struvite urolithiasis is the presence of struvite stones in the urinary tract of dogs.  These stones are called struvite based upon their composition and can be located in the dog’s bladder, urethra, or ureters.

The most common symptoms noted in dogs are listed below.  Clinical signs are also being listed.

• Frequent urination
• Dysuria (straining to urinate)
• Abnormal urinary stream - your dog may lift his leg to urinate and only a few drops will come out, then after a short pause, maybe a few more drops may fall out.
• Urinating in inappropriate places
• Cloudy or bloody urine (hematuria)
• Increased thirst frequently is noted
• Some dogs have no symptoms at all

Clinical signs are caused by macroscopic uroliths as opposed to microscopic crystals as the larger uroliths interfere with urine flow and can irritate mucosal tissues that results in:

• Dysuria (straining)
• Hematuria (blood in urine)
• Stranguria (slow and painful urination due to muscle spasms of urethra and bladder)

Types

Types of struvite urolithiasis can be called bladder stones, kidney stones, ureter stones and urethral stones based upon their location within the urinary system.  These are the types of uroliths found in dogs:

• Nephrolithiasis - stones located in the kidneys
• Ureterolithiasis - stones located in ureters
• Uro cystolithiasis - stones located in the bladder
• Urethrolithiasis - stones located in the urethra

Types of uroliths (stones) are determined by the mineral of which they are comprised.  Ninety to ninety-eight percent of uroliths are a composite of minerals and it is this composite that helps to determine what the urolith is called.

Basically, the normal ph of dog urine falls into the slightly acidic range.  The urine is laden with mineral salts and other compounds from waste products resulting from the metabolic process.  The mineral struvite is a common dissolved component in normal dog urine and this mineral will remain in a dissolved state as long as the urine remains acidic and as long as it is not too concentrated.  If the urine gets too concentrated or becomes alkaline, then the struvite crystals can fuse together to form uroliths (stones) of various sizes and in various urinary system locations.  The causes of these urologic changes:

• Alkaline urine
• Steroid therapy
• Abnormal retention of urine
• Urinary tract infection
• Diets high in grains or starches that raise the alkaline ph in urine

A few causes of alkaline urine:

• Certain kidney diseases
• Long-term use of diuretics or antacids

A number of tests and imaging methods will likely be utilized to diagnose struvite urolithiasis in dogs.  A urinalysis can reveal cloudiness or the presence of blood. Next will be the 

veterinary examination which will involve palpation or feeling for the struvite stones in the bladder if the dog is fairly relaxed and not in much pain. If bladder stones are tiny and too small to feel through the palpated exam, an x-ray of the bladder will show the stones.

Ultrasound and radiograph as imaging tools are also useful for viewing the stones to assess size and location. While ultrasound and radiographic imaging will show the stone, it won’t tell your veterinarian the composition of the stone.  Laboratory evaluation will be required to identify the composition.

If no specimen or sample of stone is available, based on urine analysis, alkaline urine, and imaging of the stone, your veterinarian will likely make an educated guess as to the composition of the stone and make the treatment plan accordingly.

Diet

A special therapeutic diet is used when the risk of obstruction in the urinary tract is low. These diets have limitations on protein, phosphorus and magnesium and are designed to help the urine to reach an acidic ph level of less than 6.5. Diet also helps to dissolve the stones and help to discourage the development of future ones. 

Antibiotic therapy will likely be started as well because most dogs suffering from struvite bladder stone have been found to have developed them after a recent urinary tract infection.  An increase in water consumption will be recommended to help dilute the urine.  If this treatment is chosen, the pet will require urinalysis and bladder x-rays to follow the progress of the dissolution of the stones.  These tests will need to be performed every 4 to 6 weeks during the treatment.

Urohydropropulsion

Retrograde urohydropropulsion is defined as the use of a catheter and lubricant to relieve urethral obstruction by gently propelling uroliths back into the bladder.  If the stones are very small, it is possible to pass a specialized catheter into the bladder and flush the stones out (urohydropropulsion).  The dog will need, at a minimum, heavy sedation but more likely general anesthesia will be required to complete this procedure.  The use of a cystoscope will enable the veterinary caregiver to remove the stones or collect samples for lab testing, this bypasses the need to cut open the abdomen and bladder.

Surgery  

This will be strongly recommended by your veterinarian in those cases in which the dog has a large number of stones, if increased risk of obstruction exists, or if the pet owner desires the quickest resolution to the problem.  Since male dogs have higher risks of obstruction of urinary tract than do females,this fact may cause the strong recommendation from your veterinarian for surgical intervention.  Surgical intervention is also needed if attempts to dissolve the stones have failed or if stones are of mixed composition of mineral types. Surgical intervention is required for any obstructions as death of the animal can occur within days.

Another treatment option is to utilize ultrasound dissolution which may be available at some referral centers.  This option uses high frequency ultrasound waves to break up stones into tiny particles that will more easily be flushed out of the bladder.

For those dogs who have experienced struvite bladder stones, you should expect that your veterinary doctor will prescribe a therapeutic diet for the long term in attempts to eliminate or reduce the formation of future stones. This diet will not be the one used to dissolve the stone during the treatment phase but will be lower in protein, phosphorus and magnesium to aid in keeping the urine acidic. Medications may be used to keep the urine acidic.  Your pet will require careful and regular monitoring of urinalysis and signs of bacterial infection.  Bladder x-rays and urinalysis will be needed about one month after successful treatment, whether the treatment was surgical or dietary.  And, these tests should be continued every 3 to 6 months for the rest of the dog’s life.