Dogs can form calcium oxalate uroliths following successful management of struvite (magnesium ammonium phosphate hexahydrate) uroliths, and vice versa. Sometimes both struvite and calcium oxalate are present in the same urolith. When this occurs, the likelihood of an initial episode of calcium oxalate urolithiasis, which has predisposed the patient to infection-induced struvite urolith formation, should be considered. In those situations where dogs have documented occurrences of both calcium oxalate and struvite urolithiasis, uncontrollable risk factors (defective inhibitors of crystal formation and defective inhibitors of crystal aggregation) may be present. This scenario creates a therapeutic paradox in that control of some risk factors for struvite urolith formation is opposite to that recommended for prevention of calcium oxalate urolith formation.
- If struvite urolithiasis is associated with urease-positive urinary tract infections, appropriate therapy should be devised to eradicate the UTI and prevent its recurrence. Eradication of urease-producing pathogens will prevent recurrence of infection-induced urolithiasis.
- In addition, further medical management should be designed to minimize risk factors associated with calcium oxalate urolith formation. When considering dietary management, we recommend that emphasis be placed on minimizing recurrence of calcium oxalate uroliths, since medical management currently cannot dissolve this type of urolith. Should struvite uroliths recur, dietary management often can dissolve them.
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If uroliths should recur despite control of risk factors, they may be removed non-surgically by voiding urohydropropulsion, if detected early. Uroliths removed by voiding urohydropropulsion should be quantitatively analyzed. If attempts at non-surgical urolith removal are unsuccessful, surgery remains the most reliable way to remove active uroliths from the urinary tract. We emphasize, however, that surgery may be unnecessary for clinically inactive uroliths.
Further references:
Lulich JP, Osborne CA, Unger LK, et al: Nonsurgical removal of urocystoliths by voiding urohydropropulsion. In Journal of the American Veterinary Medical Association. Vol 203, pp. 660-663, 1993
Osborne CA, et al.: Canine and Feline Urolithiases: Relationship of Etiopathogenesis to Treatment and Prevention. In Canine and Feline Nephrology and Urology, Osborne and Finco 1995, pp 798-888.
Osborne CA: The Management of Recurrent Urolithiasis In Patients with a History of Calcium Oxalate and Struvite Urolith Formation. In Partners In Practice, Hill's Pet Nutrition pub. Vol V, No. 1, 1992.
Osborne CA, et al.: Canine Urolithiasis. Small Animal Clinical Nutrition 4th ed., 2000, pp. 605-688.
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