Cystine urolithiasis-free duration after first occurrence and treatment is longer for castrated dogs than for sexually intact male dogs.

Objective: To evaluate outcome in 60 dogs with cystine urolithiasis treated with surgical removal with and without castration and postoperative therapeutic diet to determine frequency of recurrence and urolith-free duration.

Methods: Patient records were reviewed for dogs with documented cystine urolithiasis from September 2010 to December 2020. Medical records, client interviews, and referring veterinarians were contacted to document the absence of clinical signs associated with subsequent urolith formation and to evaluate risk factors for urolith reoccurrence.

Results: 80 patients were identified with cystine uroliths, with 60 qualifying for inclusion in the study. Seven dogs were neutered prior to surgery, and 25 dogs were neutered at the time of the first surgery. Recurrence occurred in 20 dogs; 17 of those patients were intact (85%) at the time of recurrent urinary signs. Of the 20 dogs with recurrence, 50% (10 of 20) were being treated with dietary modifications.

Conclusions: The risk of recurrence among neutered pets was 23% versus 47% for intact pets, but this difference was not statistically significant; however, neutered pets had a longer urolithiasis-free duration. There was no statistically significant difference in risk of recurrence and urolith-free duration between pets with and without therapeutic diet management, (30% vs 32.5%) respectively. Multivariant analysis showed no significant interaction between surgical intervention with therapeutic diet, with nonsignificant hazard ratios (HRs) for neuter status (HR = 0.503), diet (HR = 1.056), and their interaction (HR = 4.32 to 9).

Clinical Relevance: Sexually intact (vs castrated) male dogs should be monitored more closely for recurrence of surgical cystine urolithiasis.