CBD stones may cause jaundice, cholangitis, pruritus and biliary pancreatitis. The prevalence of CBD stones increases with age and treatment is difficult. At present, surgical choledochotomy is no longer always the therapy of choice due to its invasive character and associated morbidity and mortality. Since the introduction of therapeutic ERCP in 1974, there has been much progress regarding this procedure for treating CBD stones[11]. However, in clinical practice it is not uncommon to see patients with large CBD stones, which cannot be removed by such conventional techniques. For difficult cases, various adjuvant treatments such as ESWL, electrohydraulic lithotripsy and lasers are recommended rather than just using a mechanical lithotripter[12].

Kidney lithotriptors can be used when performing ESWL of bile duct stones, and its efficacy in treating CBD stones has been reported in many studies[13,14]. But for some difficult cases, fragmentation alone may not be adequate because of size and other reasons[15]. Many researchers advised performing ERCP after ESWL to facilitate ductal clearance and decompression, clearing fragments and to address any ductal strictures by balloon dilation with or without stenting[16]. Tao et al[17] reported that using cholecystokinin during ESWL can facilitate endoscopic clearance of large CBD stones. Therefore, ESWL overcomes the problem of the stone size by fragmenting the stones and reducing the stone burden, thus facilitating endoscopic clearance in the following ERCP procedure. According to the literature, complete clearance of CBD stones can be achieved in 40%-75% of the patients[18,19].

Tandan et al[20] reported improved stone clearance of large CBD stones using ESWL prior to ERCP. In the study, patients with large CBD stones were subjected to up to 7 ESWL sessions before CBD stones were decomposed to fragments less than 5 mm in diameter. The authors concluded that stones were best fragmented at a kV intensity of 4 (range, 1 to a maximum of 6, corresponding to 11000-16000 kV) and a frequency of 90 shocks/min. Patients were subjected to ESWL at a shock wave frequency of 90/min with continuous saline irrigation contributing to the complete fragmentation of CBD stones.

In our study, patients in the ESWL + ERCP group were subjected to an ESWL session 4 h prior to ERCP. The stones may or may not have been fragmented to a size less than 5 mm in diameter; however, in each case the following ERCP was performed as planned. The results were satisfactory. Although the rate of successful CBD clearance was similar in the first treatment session between the two groups (74.2% vs 71%, P = 0.135), a session of ESWL prior to ERCP showed a higher clearance rate in the second treatment session (84.4% vs 51.6%, P = 0.018) and in the overall outcome (96.0% vs 86.0%, P = 0.029). The rate of mechanical lithotripsy use also differed between the two groups (20% vs 30%, P = 0.025), potentially accounting for the statistical difference observed in the relative duration of ERCP (43 ± 21 min vs 59 ± 28 min, P = 0.034). Using the conventional methods (balloon or basket), stone clearance was high in both groups, while the removal of extremely large stones and successful clearance rates of mechanical lithotripsy differed significantly between the two groups (20% vs 30%, P = 0.025; and 92.0% vs 75.0%, P = 0.041, respectively). Although these differences might be due to various factors, such as the extent of ERCP, the size of the stone and the dilating balloon, the shape of the stone and the bile duct, we think that including a session of ESWL prior to ERCP is an important tool for reducing the rate of mechanical lithotripsy use and ERCP procedure time. In addition, it shows promise in terms of improving the clearance rate of extremely large stones.

In previous studies, stone fragmentation and clearance were influenced by the presence of a downstream stricture, stone size and location[21]. In our study, there was no significant difference in complete CBD stone clearance according to stone size or location, or accompanying downstream stricture. Strictures in the CBD were dilated using balloons in nearly all the cases. Such procedures did not have any negative impact on stone clearance in our study. Several authors reported that a stent should be placed for bile drainage if CBD stones could not be removed in the first session of ESWL[22-24]. Biliary stent placement has been established as a convenient and minimally invasive treatment for difficult stones, and we adopted it in our series.

Post-ERCP complications such as moderate pancreatitis, cholangitis and mild haemorrhage were similar in the two groups and are consistent with previous reports[25,26]. Post-ERCP pancreatitis is the most common complication of ERCP despite technological developments and improved endoscopist skill levels. The possible causes of the low rate of pancreatitis observed in the present study include proper patient selection for ERCP with appropriate indications and guidewire cannulation[27]. In our study, the presence of NBT helped us selectively cannulate CBD when performing ERCP, thus avoiding cannulating and excessive injection of the CBD. There was no increased incidence of pancreatitis after ERCP in the ESWL + ERCP group.

A number of rare and serious complications have been reported following ESWL[28-31]. These include perirenal hematoma, biliary obstruction, bowel perforation, splenic rupture, lung trauma and necrotizing pancreatitis. These severe complications did not occur in our study, probably because of accurate targeting achieved by the third-generation lithotripter and reduced patient movement. Pain at the site of shock wave delivery, skin ecchymosis, abdominal pain, occasional fever and hemobilia were observed in some of our patients. These complications were mild and minimal, all being managed conservatively without extension of hospital stay.

A recurrence rate of 14% for post-ESWL CBD calculi at 1-year follow-up has been reported[32]. Therefore, stones should be removed as completely as possible. In our study we found that saline irrigation is helpful and should be repeated several times until all the bile drainage is completely clean.

ESWL appears to be a valid, low-cost technique applicable to challenging bile duct stones and its utilization may be extended to urology. Hence, the same device can be used by different medical staff in hospitals, thus reducing management costs.

The main limitation of our study was that we evaluated short-term outcomes, such as successful clearance in the first and second session of ESWL + ERCP and complications of the procedure. However, long-term follow-up of the failed cases was not evaluated and included in this study. Second, the interpretation of the degree of CBD clearance could be subjective. Also, the treatment effect may be influenced by the skills of the treating physician. Other limitations include performing the study at only one centre and the relatively small number of patients. Further prospective randomized studies are therefore needed to prove efficacy and evaluate cost efficacy.

In conclusion, a session of ESWL prior to ERCP is an excellent therapeutic modality for problematic and large common bile duct stones, offering a high clearance rate, particularly in terms of removing extremely large CBD stones. This procedure moreover reduces the use of mechanical lithotripsy and ERCP procedure time. Therefore, we propose that a session of ESWL prior to ERCP is an effective and safe treatment for endoscopic removal of challenging and large CBD stones.