Response to letter regarding “Benign feline ureteral obstruction in cats: Outcome with medical management”

Thank you for the opportunity to address the letter of Drs Aronson, Schmiedt, Bartges, Monnet, and Hardie.

We thank the authors for their interest in our study.

“Standard of care” specifies appropriate treatment based on scientific evidence and collaboration among medical professionals. Given the large body of evidence (11 retrospective studies in 706 cats with benign feline ureteral obstruction [BUO] treated with placement of a subcutaneous ureteral bypass device [SUB] over the past 12 years) with similar good outcomes and long-term survival, regardless of cause, we believe that SUBs can be considered standard of care for the treatment of BUO. Standard of care is not an exclusionary term suggesting that no other treatment is indicated or acceptable. Standard of care can vary from 1 institution to another depending on the expertise and experience of medical professionals.

A striking feature of studies of SUB placement for BUO is the similarity in outcomes and complication rates when performed with fluoroscopic-guidance in different hospitals around the world regardless of experience. We agree with the authors that extensive microsurgical training and experience are important prerequisites to obtain the best results when performing ureteral surgery, given the difficulty in operating on the ureters of cats. Such extensive training and experience are not prerequisites for SUB placement.

The authors cite a study in 12 cats with obstructive ureteroliths that underwent ureteroneocystostomy with 92% survival to discharge and median survival of 321 days.¹ Three patients (25%) had to be returned to surgery for complications (uroabdomen, abdominal wall dehiscence). Unfortunately, only 2 cats had ultrasound follow-up 2 months after surgery, 1 of which had persistent hydronephrosis and hydroureter, suggesting persistent obstruction.² Stabilization or improvement of serum creatinine concentration cannot be used as sole indicators of successful surgery because the contralateral kidney can compensate and increase glomerular filtration rate, thus lowering serum creatinine concentration. This study reported that 3/11 (27%) cats had urinary tract infection and positive urine culture results. Positive urine cultures are documented in 22% to 29% of cats with CKD without a urinary implant and not having undergone urinary tract surgery.^{3, 4} Therefore, positive urine culture rates of 25% to 30% in cats with CKD may not represent a complication of SUB placement, as mentioned by the authors, because similar rates are reported after surgery without an implant and in cats with CKD. In another study referenced by the authors,⁵ no ultrasound follow-up was described and urine cultures only were performed when cats had lower urinary tract signs. It is expected that studies in which urine cultures are systematically collected post-operatively will identify higher positive urine culture rates than studies in which serial urine cultures are not performed in asymptomatic patients. Furthermore, because of a lack of routine ultrasound follow-up in some surgical studies, reobstruction or complications such as strictures at the site of surgery could be missed. Retrospective studies of SUB device placement in cats provide long-term follow-up including serial serum creatinine concentration measurements, ultrasonographic evidence of resolution of obstruction by a decompressed renal pelvis and ureter, and serial urine cultures. We therefore respectfully disagree with the authors that “SUB device has been associated with a much higher incidence of infection rate and need for revision surgery.”

To our knowledge, routine SUB irrigation has not been shown to decrease the rate of mineralization or infection and is not obligatory after SUB placement as stated by the authors. Because BUO occurs primarily in cats with kidney disease, monitoring is recommended every 12 weeks or more frequently depending on the International Renal Interest Society stage.⁶ We therefore believe that routine follow-up in cats with kidney disease and monitoring of serum phosphorus, potassium, calcium, and creatinine concentrations along with body weight, body condition score, hydration status, and blood pressure are essential aspects of the management of cats with kidney disease with or without a SUB.

The authors raise an interesting question regarding continued discomfort despite relief of the obstructive component in cats with BUO secondary to ureteral stones. Although we have not appreciated this concern clinically and it has not reported in cats, it is certainly worth investigating. Distension of the urinary tract proximal to the obstruction is believed to be the origin of discomfort (ie, ureteral colic) in human patients with ureteral obstruction. Recently, asymptomatic passage of stones in people has been reported in 33% of patients.⁷ In a study of stone passage after SUB placement in cats with BUO, 54% of ureters became patent.⁸

We sincerely hope that exchanges between veterinary internists and surgeons experienced in the treatment of BUO will foster further collaborative research into the disease and improve treatment outcomes. Unfortunately, given the current veterinary literature available, identification of individual patients with BUO (with different causes and sites of obstruction) that would most benefit from medical management, surgery (eg, ureterotomy, ureteroneocystostomy) or SUB placement is not clear and merits further investigation.