Reply to Drs. Liao and Peng

We appreciate the comments of Drs. Liao and Peng and their interest in our study [1]. They raised several issues as follows: (i) the high migration rates of the fully covered self-expandable metal stents (FCSEMSs) owing to their short lengths; (ii) the risk of sludge formation in the plastic stents; and (iii) an underestimation of patient factors and the relative length of the FCSEMS to the stenosis, which are related to stent patency.

The average length of the FCSEMSs used in this study was 5 cm, which is the shortest length among the commercially available metal stents. The proximal end of the FCSEMS was placed 1 cm above the top of the stricture to prevent obstruction of the cystic duct orifice. In fact, there was only one case of acute cholecystitis (1/68; 1.5 %) in this study. Although the previous study that used mostly 6- and 8-cm FCSEMSs revealed that the stent migration rate was 14 %, acute cholecystitis occurred in 4 % of the study population [2]. In patients with a low orifice of the cystic duct, a shorter length of SEMS with an anchoring plastic stent may be recommended.

Although there are concerns that an internal anchoring plastic stent causes more sludge formation, stent occlusion due to sludge clogging was reported in one case (2.9 %) in the FCSEMS group vs. two cases (6.1 %) in FCSEMS with anchoring plastic stent group, which was not statistically different. Further research is needed to overcome the concerns raised.

We totally agree with the concerns raised about the factors associated with stent patency, including the timing of stent placement, length and severity of biliary stenosis, angulation of the common bile duct, tumor response to chemotherapy, and relative length of FCSEMS to stenosis. Although the timing of stent placement and the severity of stenosis were not fully evaluated in this study, we could assume that these factors would not have significant differences between the two groups because there was no significant difference in the initial levels of serum total bilirubin before insertion. We agree that the relative position of the FCSEMS to the stenosis is also an important factor when placing FCSEMSs. Further randomized trials with a full consideration of all these factors may be necessary to identify the patient groups that require an internal anchoring plastic stent.

Publication History

Article published online:
24 November 2021

• References

• 1 Paik WH, Woo SM, Chun JW. et al. Efficacy of an internal anchoring plastic stent to prevent migration of a fully covered metal stent in malignant distal biliary strictures: a randomized controlled study. Endoscopy 2021; 53: 578-585
• 2 Kogure H, Ryozawa S, Maetani I. et al. A prospective multicenter study of a fully covered metal stent in patients with distal malignant biliary obstruction: WATCH-2 study. Dig Dis Sci 2018; 63: 2466-2473