Letter regarding "Benign ureteral obstruction in cats: Outcome with medical management".

This letter is in reference to an article recently published in the May 2023 edition of JVIM, “Benign ureteral obstruction in cats: Outcome with medical management.”1 This study reports on the clinical characteristics and outcome of a large cohort of cats treated medically for benign ureteral obstruction secondary to a number of causes including urolithiasis, pyonephrosis, and stricture. The results of the study, identifying a higher success rate of medical management than previously reported, are encouraging, and offer a reasonable alternative for owners who decline surgical options for their cat. We have no problem with this study, but rather take issue with statements made within the manuscript relative to surgical treatment of ureteral obstruction in cats. In the Introduction and in the Discussion, the authors state that the placement of a subcutaneous ureteral bypass (SUB) device is the standard of care for this patient population. Unfortunately, this statement is without merit and misleads the reader regarding optimal treatment for these patients. To support their claim, the authors reference two retrospective, descriptive manuscripts that identify a hospital discharge rate of 94% and median survival times (MST) of 821-827 days.2, 3 The authors also report complications from those studies including device kinking (3%-10%), luminal mineralization (17%-25%), and chronic infection (24%-25%). In our review of the current literature on SUBs, including the 2 manuscripts previously referenced, mortality before discharge ranged from 6% to 21% (equivalent to a discharge rate of 79%-94%) and MST ranged from 274 to 827 days (references available upon request). Although not a comprehensive list, some of the more common complications reported in those studies include device kinking (4.6%-10%), luminal mineralization (4%-25%), noninfectious cystitis (9%-38%), and urinary tract infection (20.8%-35.7%). Additionally, postoperative bacteriuria has been identified in up to 36% of cats after SUB placement (references available upon request). These complication rates identified in multiple studies are clinically important; overall complication rates are reported as high as 88%, but more commonly approximately 48%-56%. Additionally, the need for revision surgery ranged from 8% to 27% and, in a recent multicenter report published in JVIM, transmural migration of 11 devices within the digestive tract also resulted in the need for a second surgical procedure.4 In human medicine, because of the morbidity and mortality associated with permanent urinary implants, ureteral bypass devices are reserved most commonly for patients with end stage genitourinary cancer. Similar to human medicine, the use of natural tissues to address an obstruction in veterinary medicine avoids many inherent complications associated with implants. The small size of the feline ureter necessitates appropriate training in the use of magnification, which is critical to success with these cases. It has been our observation that complications including leakage and stricture are substantially decreased when appropriate magnification is used. Although the learning curve to become proficient in microsurgery is steeper than developing proficiency in successful SUB placement, it is achievable with appropriate training. In the United States, courses in microsurgery are readily available for both human and veterinary medical clinicians interested in learning these techniques. In their Introduction, the authors mention 4 studies to reference high complication, mortality, and recurrence rates associated with standard surgical techniques. In a recent publication on ureteral surgery by Wormser et al., referenced by the author, 63 cats underwent a ureterotomy alone and 11 cats underwent a neoureterostomy alone. Intraoperative magnification was used for each technique. The incidence of perioperative complications for these cats was 3% (2/74). Survival to discharge was 92% (a similar survival to discharge was reported by Lorange et al.) and the MST was 1519 days, almost twice the MST reported for SUB placement. Two of 74 cats (3%) were diagnosed with uroabdomen and the incidence of infection was 2%.5, 6 In Kyles et al., uroabdomen developed in 12% of cats that did not have a nephrostomy tube placed, with the majority treated successfully by revision surgery. The 6, 12, and 24-month survival rates after surgery in that study were 91%, 91%, and 88%.7 In a final report referenced by the authors (Culp et al.), 30% of cats were diagnosed with a uroabdomen, likely contributing to a higher mortality rate before discharge. Unfortunately, there is no mention regarding the use of magnification in that study.8 Referencing those studies, the authors mention a reobstruction rate of 22%-40%, but this rate is misleading. Reobstruction was not identified in 1 study6 and occurred in 20% and 22% respectively in 2 other reports cited.5, 7 In Kyles et al., a reobstruction rate of 40% is reported, but this percentage refers to patients managed both medically and surgically and, on careful review of the paper, the incidence of ipsilateral reobstruction after ureterotomy was 20%.7 Finally, the need for revision surgery in all 4 studies ranged from 10% to 13%. Two final points deserve mention for cats receiving a SUB device. First, current recommendations for postoperative management of the SUB device include irrigating at 1 week, 1 month, and every 3 months thereafter after surgery. Additionally, the need for revision surgery ranges from 8% to 27%. Although regular follow-up medical management is recommended for this patient population because of their underlying renal disease, the long-term financial obligation for SUB device maintenance, in additional to medical management of chronic kidney disease, can be substantial. Unfortunately, limited information exists in the current literature regarding the additional financial commitment necessary to manage these patients. Finally, in humans, ureteral stones are known to be associated with considerable pain and discomfort and, given the high morbidity associated with long-term use of urinary implants, techniques in human urogenital surgery prioritize stone removal and short-term use of urinary implants. Measuring pain in cats presented with ureteral stones has not been objectively studied and likely presents an important clinical challenge. Based on the experience in human medicine, one should assume that these patients are likely not pain-free, which should be taken into consideration when making treatment recommendations. Although SUB devices offer a reasonable palliative alternative in some cases, use of natural tissues in surgical techniques should always be a priority. Additionally, given that standard surgical options and SUB placement appear to have similar survival to discharge and re-obstruction rates and that SUB devices have been associated with a higher rate of infection and need for revision surgery, stating that the SUB device is standard of care for this patient population is not justified.