Abstract
We noted that in certain aspects of the study, the methods were weak and the results/conclusions generated could be misleading. The study included 181 patients (330 stents) with just under half of the patients having two or more stents. The majority of the patients were stone formers, and the mean indwelling time was 53 days. Data on the median indwelling time would also have been relevant. Overall, the indwelling times were quite long (with a very wide range) compared with practices in many other countries, and the reasons for this were unclear. Similarly, the clinical relevance of microscopic and macroscopic encrustation is unclear.
The methods used to assess encrustation and incrustation were quite subjective, prone to bias, and difficult to quantify objectively. It would have been more scientific to perform these assessments using standardized methods, such as spectrometry or electron microscopy. 1 Similarly, a guidewire-based assessment of incrustation, although relatively easy to perform clinically, is operator dependent with a significant potential for bias.
It is well known that multiple factors contribute to the rate and amount of encrustation. These include urine composition (lithogenicity), presence of bacteria/conditioning films, and duration of use, among others. 2,3 The relative importance of any one factor can differ significantly, however, with the strong possibility that more than one factor is in action at a given time. The current study has tried to assess en/incrustation as a linear function of stent indwelling time. This is unlikely to be the case clinically, given the known interplay between many contributing factors. The results of this study also indicate that although the proportion of patients with encrustations increases with the dwell time, indwell time may not be the main factor behind formation of encrustations. Irremovable stents had a mean dwell time shorter (31 days) than the mean time for the whole group (53 days), and stents resisting removal were indwelling for as little as 14 days.
It is relevant to note that other factors that could influence en/incrustation have been studied experimentally in both static and dynamic models. 1 These include the material of the stent, mechanical and surface properties, resistance to degradation, and influence of conditioning films as well as urine volume. The many perceived advantages from such experimental studies, however, have not generally been found to result in significant clinical advantage in terms of reducing stent-related morbidity.
Table 1 presents a somewhat misleading impression about the type and manufacturer of the stents. In a small proportion of patients, different types of stents were used, with no reason being given for this and no comment as to whether there were any differences in the amount of encrustation. The results could be similar for any type of stent if used for similar durations in the same group of patients. To date, there are no clinical data to demonstrate superiority of a particular stent type or manufacturer with respect to the development of en/incrustation, clinical outcomes, and, most importantly, impact on the stent-related morbidity and health-related quality of life.
The assessment of stent discoloration and the proposed basis for its development as well as its relation to encrustation and morbidity are speculative. There are no strong data in the literature on stent coloration and presence of infection that would be clinically relevant, especially when one takes into account the relatively shorter indwelling times for stents in many regions. Similarly, the authors' suggestion of 3 months of stent dwell time (Kaplan Meier curve) should not be used in isolation, given the probability that other factors significantly influencing stent en/incrustation are at work in patients with urinary calculi. Although the ideal indwelling time is hard to decide, stents should be removed at the earliest opportunity, and each case should be considered on its own merit.