Canine Urolithiasis

Urolithiasis is a disease of the urinary tract that is characterized by the formation of calculi or uroliths (stones). Crystals form in urine when the concentration of its constituents exceeds a critical level of saturation. More than 80% of uroliths in both dogs and cats are composed of magnesium ammonium phosphate (struvite) or calcium oxalate. However, a major difference between struvite urolithiasis in cats and dogs is that most struvite uroliths in cats are not associated with urinary tract infection (sterile struvite), while urinary tract infection is common in dogs with struvite urolithiasis. Other, less frequently seen mineral composites, include ammonium urate, xanthine, cystine, calcium phosphate, silica, and dried, solidified blood (cats).2 Dietary factors can profoundly influence urolith formation. Accurate identification of the mineral composition of uroliths is important because dietary treatment or management must be directed toward the specific type of urolith.



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Canine struvite urolithiasis is often associated with bacterial urinary tract infection. Bacteria create an increasingly alkaline environment and conditions that are ideal for the formation of struvites. Bacteria commonly found to cause urinary tract infection are Escherichia coli, Staphylococcus species, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis.3

Treatment of infection-induced or sterile struvite urolithiasis involves either surgery to remove the uroliths or medical therapy. Medical therapy of infection-induced struvite typically involves the use of a calculolytic diet (such as Hill's Prescription Diet; Hill's Pet Nutrition, Topeka, Kansas, USA). A typical calculolytic diet acidifies the urine (increases struvite solubility), has decreased substrate for urease-producing bacteria (Bacteroides multiacidus, Bifidobacterium bifidum, Bifidobacterium infantis, Clostridium symbiosum, Eubacterium aerofaciens, Eubacterium lentum, Fusobacterium necrophorum, Fusobacterium varium, Lactobacillus fermentum, Staphylococcus asaccharolyticus, Peptostreptococcus), and decreased levels of magnesium and phosphorus.4. Antibiotics for 4 weeks after apparent urolith dissolution are often administered.

Medical dissolution for both sterile and infection‐induced struvite uroliths is highly effective and avoids the risks and complications of anesthesia and surgery. In many cases, dissolution is less expensive than surgery. Sterile struvite urocystoliths usually dissolve in less than 2–5 weeks. Minimally invasive procedures are associated with shorter hospitalization, and perceived fewer adverse effects, fewer residual stones because of improved visualization, and possibly lower stone recurrence rates compared to surgical cystotomy.5

Because it is not possible to dissolve calcium oxalate calculi through diet and other means, surgery is the only method of treatment for calcium oxalate urolithiasis. However, dietary changes can help to prevent recurrence of the condition by reducing urinary saturation with calcium oxalate. These diets should promote increased urine volume, preferably through the addition of water to the food.

Cystine urolithiasis occurs in dogs with an inherited defect in cystine (a component of many proteins) metabolism, resulting in cystinuria (presence of cystine in the urine). Since cystine is relatively insoluble, particularly in acidic urine, its accumulation leads to the formation of cystine uroliths. Dissolution and prevention of recurrence of cystine uroliths can be achieved through:

  • Increased water intake to increase urine volume
  • Reduction of dietary cystine to reduce cystine excretion
  • Alkalinization of urine (with bicarbonate or citrate) to increase cystine solubility
  • Administration of compounds such as D-penicillamine or 2-mercaptopropionylglycine (2-MPG), which convert cystine to a more soluble compound.

Ammonium urate urolithiasis occurs mostly in the Dalmatian and in dogs with portosystemic shunts when conversion of uric acid to allantoin in the liver is impaired. Surgical relief of obstruction may be required in some cases. In others, dissolution and prevention of recurrence of ammonium urate uroliths can be achieved through:

  • Restriction of dietary protein
  • Supplementation with potassium citrate to promote neutral or slightly alkaline urine
  • Increased water intake
  • Administration of allopurinol which decreases uric acid production.

References

  1. D.R. Lane. Veterinary Nursing
  2. Comparison of three techniques for the diagnosis of urinary tract infections in dogs with urolithiasis. Gatoria IS, Saini NS, Rai TS, Dwivedi PN.
  3. Nancy E. Rinkardt and Doreen M. Houston. Dissolution of infection-induced struvite bladder stones by using a noncalculolytic diet and antibiotic therapy
  4. Urease-Producing Species of Intestinal Anaerobes and Their Activities. K. SUZUKI,l* Y. BENNO,' T. MITSUOKA,' S. TAKEBE,2 K. KOBASHI,2 AND J. HASE2 The Institute of Physical and Chemical Research, Wako, Saitama, 351 Japan,' and Faculty of Pharmaceutical Sciences, University of Toyama, Gofuku, Toyama, 930 Japan2
  5. ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats. J.P. Lulich,corresponding author 1 A.C. Berent, 2 L.G. Adams, 3 J.L. Westropp, 4 J.W. Bartges, 5 and C.A. Osborne 1
  6. J Vet Intern Medv.30(5); Sep-Oct 2016



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