The Dwell Time of Indwelling Ureteral Stents—The Clock is Ticking But When Should We Set the Alarm?

The Dwell Time of Indwelling Ureteral Stents—The Clock is Ticking But When Should We Set the Alarm? STENT encrustation is a critical concern that often directs the duration of stenting. Previous studies have suggested that 48% of stents will be encrusted even if removed before the 3-month mark is reached.1 In addition, longer stent durations lead to greater patient discomfort.2 Evaluating conditions at high risk for encrustation (such as pregnancy) or conditions at low risk might help not only tailor the recommended dwell times but also elucidate the mechanisms of stent encrustation. One group of patients who seem to tolerate ureteral stents well in terms of symptoms and encrustation are those with malignant ureteral obstruction. In this issue of The Journal Izumi et al (page 556) reported that despite using relatively small ureteral stents (4.8 to 6Fr) the median indwell time was almost 8 months. Patients with gynecologic and urological cancers were successfully treated for longer times than those stented for other malignancies. Unfortunately stone formers do not fare so well. Also in this issue Weedin et al (page 542) evaluated the impact of proximal ureteral stone burden on the management strategy for forgotten stents. Of their cohort 89% was stented for stone disease. Although mean stent duration was more than 2 years, 94% of patients could still be treated endoscopically. They demonstrated that computerized tomography was more accurate to stage the amount of proximal stent encrustation, a critical prognostic variable for the need for multiple procedures and the risk of surgical complications. Interestingly the duration of stenting did not correlate with the need for multiple surgeries, suggesting that other variables are more impor-

tant in determining the complexity of encrustation. What remains unanswered is why some individuals are predisposed to proximal stent encrustation. Proteomics evaluations of stent biofilms suggest that although immunoglobulins and Tamm-Horsfall protein bind early to stent surfaces, it is the highly positive charged histones H2b and H3a that correlate with stent encrustation.3 Other studies suggest that keratins form the base of biofilms within 4 to 72 hours of implantation.4 Identifying specific proteomic targets to inhibit biofilm and stent encrustation may lead to extension of indwelling ureteral stent times. Is it possible that urinary proteomics or urinary metabolic evaluations might identify those at risk for encrustation and direct adjuvant medical therapy to prevent this outcome? Why are ureteral stents better tolerated by patients with stents for malignancy? For now the key to prevention is patient education. Despite the fact that the patients in this series were undoubtedly counseled on the seriousness of the situation, 10% with retained stents again failed to follow up for their planned surgical removal and were subsequently lost to followup. Where are they now? Manoj Monga* Stevan Streem Center for Endourology & Stone Disease Glickman Urological & Kidney Institute Cleveland Clinic Cleveland, Ohio

* Financial interest and/or other relationship with Gyrus-ACMI, Boston Scientific, Cook Urological and Taris Biomedical.

REFERENCES 1. el-Faqih SR, Shamsuddin AB, Chakrabarti A et al: Polyurethane internal ureteral stents in treatment of stone patients: morbidity related to indwelling times. J Urol 1991; 146: 1487. 2. El-Nahas AR, El-Assmy AM, Shoma AM et al: Self-retaining ureteral stents: analysis of factors

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responsible for patients’ discomfort. J Endourol 2006; 20: 33. 3. Canales BK, Higgins L, Markowski T et al: Presence of five conditioning film proteins are highly associated with early stent encrustation. J Endourol 2009; 23: 1437.

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4. Lange D, Elwood CN, Crowe A et al: Identification of conditioning film components on indwelling ureteral stents and their role in bacterial adhesion. J Endourol 2010; 24: A186, abstract PS23.

Vol. 185, 387, February 2011 Printed in U.S.A. DOI:10.1016/j.juro.2010.11.017

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