Diagnostic yield of second-line aetiological workup in patients with presumed idiopathic acute pancreatitis: a retrospective cohort study

Background: After an aetiological (first-line) workup, the cause of acute pancreatitis remains unidentified in a significant proportion of cases, a condition known as idiopathic acute pancreatitis (IAP). Methods: Retrospective cohort study involving patients with presumed IAP referred for second-line aetiological workup. The completion of first-line aetiological evaluations was assessed upon referral, and the diagnostic outcomes of second-line investigations were evaluated. Over a one-year follow-up period, we documented acute pancreatitis recurrence and patient mortality. Recurrence risk was analysed using an age-adjusted Cox regression model, stratified by treatable versus non-treatable aetiologies. Results: We identified 161 patients with presumed IAP, among whom 81 (50%) had recurrent acute pancreatitis. In total, 115 patients (71%) had a complete first-line aetiological workup. The overall diagnostic yield of the second-line aetiological workup was 25% (95% confidence interval [CI] 18–32%). Among second-line tests, the highest diagnostic yield was found for endoscopic ultrasound (34%, 95% CI 20–50%) and genetic testing (37%, 95% CI 22–53%). The most frequent aetiologies identified were biliary pancreatitis (16 patients [10%]) and pancreatitis with a genetic mutation (15 patients [9%]). Neoplasia was identified in two patients. A treatable aetiology was associated with a numerically reduced pancreatitis recurrence risk (Hazard Ratio 0.50, 95% CI 0.07–3.85, p = 0.51). No patient died during the follow-up period. Conclusion: A second-line aetiological workup can identify the aetiology in 25% of patients with presumed IAP. The most frequent aetiologies are biliary pancreatitis and pancreatitis with a genetic mutation.