Efficacy of medical dissolution for suspected struvite cystoliths in dogs

Abstract

Background: Medical dissolution of struvite uroliths in dogs is commonly recommended, but data on success rates and complications are limited.

Objectives: To evaluate the efficacy of medical dissolution for suspected struvite cystoliths in dogs.

Animals: Fifty client-owned dogs fed a therapeutic dissolution diet, with or without administration of antimicrobials, for treatment of suspected struvite cystoliths.

Methods: Single institution, retrospective case series. Medical records were reviewed for dogs with at least 1 follow-up visit. Dissolution success, complications, and possible predictors of success were evaluated.

Results: Full dissolution of cystoliths was achieved in 58% (29/50) of dogs within a median of 35 days (range, 13-167). Of 21 dogs without success, 7 each had partial dissolution, no dissolution, or undetermined outcome. Uroliths containing >10% nonstruvite mineral were common in the nonsuccess group (11/16 analyzed). Maximum urolith diameter, number of uroliths, and baseline urine pH did not differ significantly between dogs with and without success. Dissolution was more likely in dogs receiving antimicrobial therapy (OR = 16.3, 95% confidence interval 1.9-787.4, P = .002). Adverse events occurred in 9 dogs (18%); urethral obstructions were the most common, but 3 of 4 dogs with this complication were obstructed on presentation, before trial initiation.

Conclusions and clinical importance: Results support a medical dissolution trial for dogs with suspected struvite cystoliths. If no reduction in urolith size or number occurs by 1 month, a nonstruvite composition is likely, and alternative interventions should be considered. Dogs presenting with urethral obstructions should not be considered candidates for medical dissolution.

Keywords: canine; magnesium ammonium phosphate; stones; urinary tract infection.

FIGURE 1

Distribution of dissolution outcome (none, partial, or full) relative to timing of 46 follow‐up imaging studies for 29 dogs that ultimately achieved full dissolution for suspected struvite cystoliths. No dissolution is indicated by the black bar, partial dissolution by the gray crosshatched bars, and full dissolution by the gray bars

FIGURE 2

Distribution of duration of antimicrobial therapy for dogs that did or did not achieve successful dissolution of suspected struvite cystoliths. No dissolution is indicated by the black bars, and successful dissolution is indicated by the gray bars

FIGURE 3

Box and whisker plots of A, maximum stone diameter, B, Minnesota Urolith Center CALCulator data for the proportion of uroliths composed of struvite submitted from dogs that match the dog signalment, and C, baseline urine pH in dogs that had successful dissolution of suspected struvite cystoliths compared to nonsuccessful dissolution (partial dissolution, failure, or undetermined outcome). The dots represent values for each individual dog; in panel A, the closed dots represent measurements obtained through radiography and open dots are those obtained through ultrasonography. The boxes represent the 25th and 75th percentiles and whiskers represent 1.5 times the interquartile range. The success and nonsuccess groups did not differ significantly for these 3 comparisons (P = .6, .19, and .32, respectively)

FIGURE 4

Distribution of number of uroliths ≥1 mm in dogs with and without successful dissolution of suspected struvite cystoliths. The success and nonsuccess groups did not differ significantly (P = .67)

FIGURE 5

Box and whisker plots of A, urine pH and B, urine specific gravity at baseline and last follow‐up in dogs undergoing a medical dissolution trial (treatment) for suspected struvite cystoliths. The dots represent values for each individual dog that did (open dots) or did not (closed dots) achieve successful full dissolution of cystoliths. The boxes represent the 25th and 75th percentiles and whiskers represent 1.5 times the interquartile range. Both urine pH (P = .007) and urine specific gravity (P < .001) decreased with treatment