The goal of this clinical trial is to learn if endoscopic retrograde cholangiopancreatography (ERCP) works to treat idiopathic recurrent pancreatitis (IRAP) in adults. It also clarify the efficacy of ERCP in the diagnosis of IRAP. The main questions it aims to answer are:

Does ERCP reduce the frequency of pancreatitis episodes in IRAP patients? Does ERCP contribute to identify the etiology of IRAP patients?

Participants will be randomly allocated to receive ERCP (pancreatic sphincterotomy and pancreatic stent placement) or conservative treatment and be followed for 1 year.

Recurrent acute pancreatitis (RAP) is defined as 2 or more distinct episodes of acute pancreatitis (AP) with complete resolution between each episode, and absence of irreversible structural and functional changes in pancreas. RAP has an estimated annual incidence of 8-10 per 100,000 and the recurrence rate is as high as 10-30% in AP patients. At present, biliary, alcoholic and hypertriglyceridemia are common causes of RAP. There are also a variety of causes that may contribute to recurrent episodes of AP, such as gene mutations, pancreas divisum, ampullary neoplasms and sphincter of Oddi dysfunction. About 80% of RAP patients can be identified through routine clinical investigations (include proper history, physical examination, imaging examination); however, the etiology in up to 20% of cases still not be clarified and these patients is called idiopathic recurrent acute pancreatitis (IRAP).

Endoscopic retrograde cholangiopancreatography (ERCP) is an important minimally invasive treatment for pancreatic diseases. However, the role of ERCP in IRAP patients with normal biliary and pancreatic anatomy remains controversial and there is a lack of high-quality clinical research evidence on endoscopic treatment of IRAP. In a small sample size (N=34) open-label randomized controlled study, IRAP patients were assigned to the experimental group with pancreatic duct stent placement and the control group with selective pancreatograms but no stent. This study demonstrated that stent placement was able to reduce the recurrence rate of AP (53% vs 11%, P < 0.02). Coté et al performed an open-label randomized trial (N=89) of ERCP with sphincter of Oddi manometry for IRAP patients. Among patients with pancreatic sphincter dysfunction, they found that biliary sphincterotomy and combination of biliary and pancreatic sphincterotomy have similar effects in preventing recurrence of AP, and there was also no significant difference between biliary sphincterotomy and sham surgery in patients with normal sphincter of Oddi manometry. However, some retrospective studies had shown that sphincterotomy works to reduce the recurrence rate of acute pancreatitis.

Currently, there is a shortage of high-quality evidence, and the wide variation in different study designs has led to controversial conclusions. Given the long-standing controversy, we propose to conduct a randomized controlled trial to investigate the efficacy of ERCP in the diagnosis and treatment of Idiopathic recurrent acute pancreatitis.

Inclusion Criteria:

1. Aged 18 to 70 years.

2. Patients diagnosed with IRAP:

   1. Previously experienced 2 or more distinct episodes of acute pancreatitis (AP) with complete resolution between each episode, and absence of irreversible structural and functional changes in pancreas. The diagnosis of AP is based on the Atlanta criteria and is documented in the medical record.
   2. The etiology of RAP remains undetermined after routine clinical investigations, including history, laboratory examination, imaging examination (CT, MRI/MRCP, EUS). Patients who still have AP episodes after elimination of the etiology also be included.

3. At least 1 episode of AP one year prior to enrollment.

4. Consent to participate in the study and sign the informed consent form.

Exclusion Criteria:

1. Prior sphincter intervention.
2. Not recovered from prior AP attack.
3. Prior pancreatic surgery.
4. Contraindications to ERCP.
5. Major mental illness or serious health problems that are not suitable for participation in the study.
6. Pregnancy or plan for pregnancy within 12 months of enrollment.
7. Other conditions that inappropriate to participant in the study.