Problem

A 10-year-old spayed female domestic shorthair cat was examined for intermittent periuria (urinating outside the litter box) of 6 months' duration and recent red discoloration of the urine. Results of physical examination were unremarkable. Analysis of a naturally voided urine specimen indicated the cat had proteinuria, hematuria, pyuria, bacteruria (cocci), and crystalluria. The urine was concentrated (specific gravity, 1.050; reference limits, 1.025 to 1.070), with a pH of 6.0. The crystals in the urine sediment had a size and shape consistent with struvite crystals (ammonium magnesium phosphate). Abdominal radiography revealed a single large, radiodense urocystolith (Figure 1). The urocystolith with or without a concurrent urinary tract infection was deemed the likely cause of the clinical signs. The owner wanted to know whether there were nonsurgical alternatives to managing urinary stones such as the one in this cat.

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Lateral abdominal radiographic view of a 10-year-old spayed female domestic shorthair cat with periuria and hematuria. Notice the radiopaque urolith (white arrow) in the urinary bladder.

Citation: Journal of the American Veterinary Medical Association 236, 9; 10.2460/javma.236.9.965

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Formulation of the Clinical Question

Struvite and calcium oxalate are the mineral types that account for most urocystoliths in cats.^a On the basis of the radiographic appearance of the urolith and presence of struvite crystalluria, a tentative diagnosis was made of urocystolith consisting of ammonium magnesium phosphate (struvite). The bacteruria was attributed to a urinary tract infection or contamination of the urine specimen during voiding.

Treatment options for struvite uroliths in cats include physical removal (cystotomy, voiding urohydropropulsion, or laser lithotripsy) or dissolution through nutritional management. Urohydropropulsion was not considered a viable option for a patient with a urolith this large, and laser lithotripsy was not readily available. Therefore, the 2 principle treatment options included surgical removal or nutritional dissolution of the urolith.

Clinical Question

For cats with struvite urocystoliths, is surgical removal or nutritional dissolution more effective for eliminating uroliths from the urinary bladder and controlling clinical signs (eg, periuria, hematuria, and pollakiuria) caused by their presence?

Evidentiary Search Strategy

A practical and efficient evidence-based approach to decision making was desired. Therefore, instead of an exhaustive literature search and critical review, a targeted literature search, directed by a consulting clinician, was used to obtain the pertinent data for evaluation. The supervising veterinarian (TP) contacted a consulting clinician (SDF) associated with a clinical consultation service available from an animal health company.^b

Experience of the consulting clinician suggested that nutritional management would be effective and result in less pain, discomfort, and complications than a surgical procedure. However, the superiority of one method over the other with respect to final outcome and control of clinical signs was unknown. Therefore, a targeted bibliographic search was performed in September 2007. The PubMed database and major veterinary textbooks (internal medicine, surgery, and clinical nutrition) were searched with the following keywords: feline, struvite uroliths, struvite stones, bladder stones, dissolution, nutritional management, and cystotomy. A 15-minute search identified several reports,^1–5 most of which described results of a single case or prospective case series study in which nutritional management was used. One retrospective case series^c described in an abstract had been conducted to evaluate the effectiveness of cystotomy for removal of various types of urocystoliths.

Review of the Evidence

Studies were evaluated with the aid of a grading system adapted for veterinary clinical nutrition.⁶ The scoring system was developed in recognition of the fact that the quality of the evidence supporting a recommendation is an important consideration when making therapeutic decisions. In this grading scheme, grade I and II evidence has the highest quality for application in the clinical environment and is associated with systematic reviews and randomized, controlled clinical trials, respectively. Grade III evidence is associated with appropriately designed, nonrandomized clinical studies; epidemiological data (cohort or case-control studies); studies that involved suitable models of disease or simulations in target species; case series; or dramatic results in uncontrolled studies. Grade IV evidence is less robust and is based on clinical experience (textbooks, monographs, or proceedings), descriptive studies, studies conducted in other species, and decisions based on pathophysiologic rationale.

For struvite urocystoliths, the strongest evidentiary value was from prospective case series studies. Two studies^4,5 involving evaluation of therapeutic foods in 59 cats with struvite urocystoliths showed that the uroliths dissolved in a mean of 4 to 6 weeks. Longer periods were required to dissolve struvite uroliths associated with urinary tract infections caused by urease-positive bacteria. Nutritional management of struvite uroliths was associated with radiographic disappearance of uroliths within 2 weeks in up to 30% of cats. Those uroliths that did not resolve with nutritional management in these studies were later removed surgically and identified as uroliths composed of other mineral types. In most patients with struvite uroliths, clinical signs resolved within 2 to 3 weeks.

In addition to the 2 aforementioned published reports, 2 unpublished, retrospective, descriptive studies^c,d were identified. Those studies revealed that incomplete removal of uroliths occurred in 4 of 29 (14%)^c cats and 9 of 66 (14%)^d dogs that underwent cystotomy for removal of urocystoliths. The results suggested that cystotomy does not always result in complete removal of uroliths in cats and dogs.

Given the aforementioned evidence, what decision would you make?

Clinical Decision and Outcome

The consulting clinician discussed the 2 options with the supervising veterinarian. Because the published reports^4,5 suggested that clinical signs of urolithiasis often resolve within a few days to a couple of weeks in affected animals and because of the pain, discomfort, and potential complications associated with surgery, use of a therapeutic food was recommended by the consultant. This plan was communicated to the cat's owner by the supervising veterinarian and accepted. A therapeutic food^e designed to aid in the dissolution of struvite uroliths was chosen. Ingestion of the food purportedly helps minimize concentrations of struvite components such as magnesium, supplies antioxidants, and results in a target urine pH of 5.9 to 6.1 to increase solubility of struvite crystals, aiding in dissolution.

The owners chose to offer both dry and moist formulations of the therapeutic food. They were instructed to feed the food exclusively and not use other foods or supplements. Bacterial culture of a urine sample was not performed, but empirical antimicrobial treatment was started with orally administered amoxicillin–clavulanic acid. Clinical signs improved within 7 to 10 days after feeding began, and radiographs obtained 3 weeks later revealed no obvious uroliths. Nutritional and antimicrobial treatments were continued for another 3 weeks. At that point, treatment was changed to a therapeutic food designed to prevent recurrence of struvite crystalluria and uroliths.^f The cat has continued on this food with no recurrence of clinical signs or radiographic evidence of uroliths for 30 months.

Discussion

The best evidence-based decisions are made when research evidence is combined with clinical expertise, owner preferences, and available resources.⁶ No formal process was used to combine the experiences of the consulting clinician with the strategic review of urolith management. In the situation described here, the consulting clinician was familiar with the basic research conducted on this topic and used the systematic review to confirm details of medical and surgical management. Thus, the therapeutic recommendation was a combination of the best evidence and clinical experience by the consulting clinician, with implementation of the plan and monitoring performed by the supervising veterinarian. This combination is commonly used in clinical practice and resulted in a successful outcome for the patient and pet owner.

In the published grading scheme,⁶ appropriately designed, nonrandomized clinical studies are categorized as grade III evidence, which offers a good level of evidence to evaluate therapeutic procedures when well-defined outcome variables indicate a quick response to the intervention (eg, dissolution or physical removal of obvious uroliths). Data from dogs with similar problems (grade IV evidence) were also considered in making a decision for the cat in this report.^c,d

Surgical removal of urocystoliths remains a viable therapeutic option when nutritional dissolution is not successful or when nutritional dissolution is not appropriate (eg, calcium oxalate urolith). However, imaging studies (radiography and ultrasonography) should always be performed immediately after surgery to confirm that all uroliths have been removed. To ensure adherence to therapeutic recommendations and detect recurrent disease, cats with a history of struvite uroliths or urinary tract infection should be reevaluated periodically. The ideal time for such follow-up has not been determined; however, it would be reasonable to perform urinalysis, urine culture, and diagnostic imaging at least every 6 months.