The diagnostic work-up and outcomes of ‘presumed’ idiopathic acute pancreatitis: A post-hoc analysis of a multicentre observational cohort

Introduction: After standard diagnostic work-up, the aetiology of acute pancreatitis remains unknown in 16–27% of cases, a condition referred to as idiopathic acute pancreatitis (IAP). Determining the aetiology of pancreatitis is essential, as it may direct treatment in the acute phase and guides interventions to prevent recurrent pancreatitis. Methods: Between 2008 and 2015, patients with acute pancreatitis were registered prospectively in 19 Dutch hospitals. Patients who had a negative initial diagnostic work-up with regard to the underlying aetiology of their pancreatitis were labelled ‘presumed’ IAP. The aim of this study was to assess the use of diagnostic modalities and their yield to establish an aetiology in ‘presumed’ IAP, and to assess recurrence rates both with and without treatment. Results: Out of the 1632 registered patients, 191 patients had a first episode of ‘presumed’ IAP, of whom 176 (92%) underwent additional diagnostic testing: CT (n = 124, diagnostic yield 8%), EUS (n = 62, yield 35%), MRI/MRCP (n = 56, yield 33%), repeat ultrasound (n = 97, yield 21%), IgG4 (n = 54, yield 9%) and ERCP (n = 15, yield 47%). In 64 of 176 patients (36%) an aetiological diagnosis was established, mostly biliary (n = 39). In 13 out of 176 of patients (7%) a neoplasm was diagnosed. If additional diagnostic workup revealed an aetiology, the recurrence rate was lower in the treated patients than in the patients without a definite aetiology (15% versus 43%, p = 0.014). Conclusion: Additional diagnostic testing revealed an aetiology in one-third of ‘presumed’ IAP patients. The aetiology found was mostly biliary, but occasionally neoplasms were found. Identification of an aetiology with subsequent treatment reduced the rate of recurrence.