Nutritional Assessment in a Dog with Urolithiasis

THE CASE

Stella, a 4-year-old, 15-lb (6.8-kg), spayed terrier crossbreed was presented for intermittent hematuria and stranguria of a week’s duration. She had been healthy previously and was up to date on vaccinations.

Physical examination revealed normal body temperature, heart rate, and respiratory rate. BCS was 5/9, and muscle condition was normal. She had a small, soft bladder and mild discomfort on caudal abdominal palpation. No urethral calculi were palpable on rectal examination.

Dietary History

Stella had been fed a commercial dry dog food, formulated to meet the nutrition requirements established by the Association of American Feed Control Officials Dog Food Nutrient Profiles for all life stages, in measured amounts according to package recommendations. She received occasional table scraps but no commercial treats or supplements.

Diagnostic Results

CBC and serum chemistry results were unremarkable. Urinalysis obtained via cystocentesis revealed a urine specific gravity (USG) of 1.052 (reference range, 1.015-1.050), a pH of 7.5 (reference range, 5.5-7.0), 51 to 100 cocci/hpf, 2 to 3 WBC/hpf, and 2 to 3 RBC/hpf. No crystalluria was observed. A urine sample was submitted for culture and antimicrobial susceptibility testing. Abdominal radiographs showed numerous round-to-ovoid–shaped, moderately radiopaque cystic calculi.

DIAGNOSIS:

BACTERIAL CYSTITIS & CYSTIC UROLITHIASIS

Infection-induced struvite urolithiasis was suspected based on the presence of bacteria and alkaline urinary pH. Female dogs are predisposed to UTIs.^1,2 Uroliths of other composition (eg, calcium oxalate) were also considered because, although struvite uroliths are typically associated with UTIs in dogs, a sterile urolith of any composition may form primarily, serving as a nidus for secondary UTI. Most uroliths in dogs are of struvite or calcium oxalate composition.³

Treatment & Outcome

Medical dissolution is recommended as a first-line treatment for struvite uroliths.⁴ Thus, a veterinary therapeutic canned diet formulated for struvite dissolution was recommended for Stella. The owner was instructed to gradually introduce additional water to the canned diet as needed to achieve a goal USG of <1.020 and to discontinue table foods to maximize diet efficacy. Based on antimicrobial guidelines, initial therapy with amoxicillin (15 mg/kg PO q8h) was instituted while awaiting culture results.⁵

Four days after initial presentation and initiation of amoxicillin therapy, final urine culture results were positive for Staphylococcus spp susceptible to several antibiotics, including amoxicillin. The owner was instructed to continue treatment with amoxicillin until urolith dissolution was documented, as bacteria in deeper urolith layers may be released during dissolution.⁶ The veterinary team confirmed with the owner that Stella had successfully transitioned to the recommended diet and that water was being added to the diet as instructed. Clinical signs started to improve with initial treatment.

At the 4-week follow-up appointment, the owner reported strict adherence to the recommended diet and resolution of lower urinary tract signs. Urinalysis showed a USG of 1.018, a pH of 6.3, and no crystalluria. Urine culture results were negative. Recheck abdominal radiographs showed a decrease in the number and size of uroliths, consistent with partial dissolution of struvite urolithiasis. The owner was encouraged to continue the diet and antibiotic treatment previously described.

At the 8-week recheck, continued owner adherence was confirmed. Stella remained clinically normal, and no uroliths were evident on abdominal radiographs. The owner was instructed to continue the therapeutic diet for 4 weeks before gradually transitioning to the previous maintenance diet, as most dogs with infection-associated struvite urolithiasis do not require long-term dietary therapy after successful dissolution. Twelve weeks after initial presentation, antibiotic therapy was discontinued. A final urine culture performed 13 weeks after initial presentation was negative.

Conclusion

In this case, a therapeutic diet in conjunction with antibiotic therapy was used to achieve resolution of urolithiasis without need for anesthesia and surgical removal. In addition to making a specific dietary recommendation, the veterinary team encouraged continued follow-up and verified the owner’s adherence to recommendations at each recheck. Close monitoring and strict adherence were key to successful medical management of infection-induced struvite urolithiasis.

ASK YOURSELF …

Diet in Disease is a series developed by the WSAVA, the Academy of Veterinary Nutrition Technicians, and Clinician’s Brief.

USG = urine specific gravity