Struvite uroliths, also referred to as calculi, are stones within the urinary tract composed of the mineral struvite or magnesium ammonium phosphate hexahydrate. They account for approximately fifty percent of the stones that affect dogs. Although any breed can be affected, the miniature schnauzer, bichon frise, dachshund
, Scottish terrier, beagle, Pekingese, and Welsh corgi are predisposed to struvite urolith formation.
Struvite uroliths are seen more commonly in females, and the average age of affected animals is six years. Clinical symptoms depend on the size and number of uroliths as well as their location in the urinary tract. Some affected animals may have no clinical symptoms.Causes Bacterial urinary tract infection is the most important predisposing factor for struvite uroliths in dogs.
Dietary factors (diet based primarily on plant proteins) or medical factors (rare kidney tubular disorders) can contribute to formation of struvite uroliths.
Long-term administration of corticosteroids, or diseases such hyperadrenocorticism, may predispose dogs to urinary tract infection and secondary formation of struvite uroliths.
What to Watch For
Passage of small volumes of urine
Increased frequency of urination
Inability to urinate
Affected dogs may be extremely ill due to kidney failure associated with urinary tract obstruction.
A thorough physical examination is very important. Occasionally, calculi may be palpated (felt) in the bladder.
Routinely performed tests include a complete blood count (CBC), biochemical profile and urinalysis. Although often within normal limits, these tests may identify abnormalities associated with kidney failure or urinary tract infection. Struvite crystals may be present in the urine, but not in all cases. Also, struvite crystals may be present in the urine of dogs that do not have struvite urolithiasis.
Additional tests include:
Bacterial culture of the urine is crucial, because bacterial urinary tract infection predisposes dogs to formation of struvite calculi.
Abdominal radiographs (X-rays) or ultrasound will detect the presence of struvite uroliths. Struvite uroliths are dense and appear as white objects in the region of the bladder on plain radiographs of the abdomen.
Depending on the size and location of the stones, recommended treatment options may be surgical or medical. If the patient is obstructed (blocked) or is having severe clinical signs associated with the presence of the stones, surgical removal is recommended.
If the stones are an incidental finding or the pet is not having severe clinical signs, dietary dissolution may be attempted. It is important for both you and your veterinarian to monitor your pet very closely during this period, as it is possible that not all stones can or will dissolve, especially if the stones are not 100 percent struvite or the pet is not under strict dietary surveillance. A diet low in protein, magnesium and phosphorus and high in salt is used in an attempt to dissolve struvite stones.
Other treatments include:
Urohydropulsion (flushing stones out of the lower urinary tract with sterile saline and a catheter) in female dogs with small (less than 5 mm diameter) bladder stones
Antibiotic therapy in patients with concurrent bacterial urinary tract infection
Fluid therapy in patients that are dehydrated or those that have severe infections, concurrent kidney failure, or have urinary blockage.
Home Care and Prevention
If your pet is receiving a stone dissolving diet, complete compliance is necessary. No snacks or other food are permitted, as these may negate the beneficial effects of the special diet. Administer all medication and return for follow-up as directed by your veterinarian.
Preventing bacterial urinary tract infection and treating infections promptly when they arise can prevent many cases of struvite urolithiasis in dogs.
Feeding your pet a diet that is magnesium restricted and one that lowers urine pH may be beneficial in preventing recurrence of struvite urolithiasis.