Further studies are needed on novel covered antireflux metallic stents

We read with interest the article by Hu et al. [1] about the success of modified metal stents with an antireflux function (ARMS) in preventing ascending cholangitis in patients with malignant biliary strictures. In their study, the authors compared newly designed partially covered ARMSs with uncovered self-expandable metal stents (ucSEMSs) with regard to the rate and frequency of cholangitis and stent patency. They noted a significantly lower rate and frequency of cholangitis in the ARMS group than in the ucSEMS group (18 % vs. 38 %; P = 0.035) and (1.9 % vs. 16 %; P = 0.022), respectively. There was also a higher median patency rate in the ARMS group compared with the ucSEMS group (13 months vs. 10 months; P = 0.044).

In this report, the authors seemed to believe that most patients with SEMSs, without the antireflux property, developed ascending type of cholangitis. However, Table 3 in the paper showed that tumor ingrowth via the stent mesh was the most remarkable and most likely cause of stent dysfunction, and could account for the lower rate of stent patency and the higher rate of cholangitis in the ucSEMS group. Indeed, 14 patents in ucSEMS group developed stent dysfunction due to tumor ingrowth (25.5 %) compared with only 3 patients in the ARMS group (5.8 %). We understand that the authors did not compare these figures statistically. We performed a chi-squared statistical analysis on these data and found that the difference was statistically significant (P = 0.012). Furthermore, the other causes of stent dysfunction (sludge formation, tumor outgrowth, stent migration, and unknown causes), occurred at similar rates in both groups of patients (P > 0.05). Thus, rather than the absence of the antireflux valve, it is possible that the absence of stent covering in the SEMS could explain the higher rate of stent occlusion, lower rate of stent patency, and higher rate and frequency of cholangitis in these patients.

Although it seems feasible and safe to insert ARMSs for the palliation of malignant distal biliary strictures, their superiority over ordinary SEMSs, especially covered SEMSs, in reducing cholangitis and achieving longer stent patency are not yet proven. Well-designed studies are still required to compare covered SEMSs with and without the antireflux mechanism. We also believe that migration due to a nonembedded stent body remains an important limitation of this newly designed stent. The cost-effectiveness of ARMS also requires investigation. Thus, it seems that there is still some way to go before ARMS becomes routinely used in clinical practice.

• Reference

• 1 Hu B, Wang TT, Wu J et al. Antireflux stents to reduce the risk of cholangitis in patients with malignant biliary strictures: a randomized trial. Endoscopy 2014; 46: 120-126