Endoscopic ultrasound diagnostic gain over computed tomography and magnetic resonance cholangiopancreatography in defining etiology of idiopathic acute pancreatitis

BACKGROUND: About 10%-30% of acute pancreatitis remain idiopathic (IAP) even after clinical and imaging tests, including abdominal ultrasound (US), contrast-enhanced computed tomography (CECT) and magnetic resonance cholangiopancreatography (MRCP). This is a relevant issue, as up to 20% of patients with IAP have recurrent episodes and 26% of them develop chronic pancreatitis. Few data are available on the role of EUS in clarifying the etiology of IAP after failure of one or more cross-sectional techniques. AIM: To evaluate the diagnostic gain after failure of one or more previous cross-sectional exams. METHODS: We retrospectively collected data about consecutive patients with AP and at least one negative test between US, CECT and MRCP, who underwent linear EUS between January 2017 and December 2020. We investigated the EUS diagnostic yield and the EUS diagnostic gain over different combinations of these cross-sectional imaging techniques for the etiologic diagnosis of AP. Types and frequency of EUS diagnosis were also analyzed, and EUS diagnosis was compared with the clinical parameters. After EUS, patients were followed-up for a median of 31.5 mo to detect cases of pancreatitis recurrence. RESULTS: We enrolled 81 patients (63% males, mean age 61 ± 18, 23% with previous cholecystectomy, 17% with recurrent pancreatitis). Overall EUS diagnostic yield for AP etiological diagnosis was 79% (20% lithiasis, 31% acute on chronic pancreatitis, 14% pancreatic solid or cystic lesions, 5% pancreas divisum, 5% autoimmune pancreatitis, 5% ductal abnormalities), while 21% remained idiopathic. US, CECT and MRCP, taken alone or in combination, led to AP etiological diagnosis in 16 (20%) patients; among the remaining 65 patients, 49 (75%) obtained a diagnosis at EUS, with an overall EUS diagnostic gain of 61%. Sixty-eight patients had negative US; among them, EUS allowed etiological diagnosis in 59 (87%). Sixty-three patients had a negative CECT; among them, 47 (74%) obtained diagnosis with EUS. Twenty-four had a negative MRCP; among them, 20 (83%) had EUS diagnosis. Twenty-one had negative CT + MRCP, of which 17 (81%) had EUS diagnosis, with a EUS diagnostic gain of 63%. Patients with biliary etiology and without previous cholecystectomy had higher median values of alanine aminotransferase (154 vs 25, P = 0.010), aspartate aminotransferase (95 vs 29, P = 0.018), direct bilirubin (1.2 vs 0.6, P = 0.015), gamma-glutamyl transpeptidase (180 vs 48, P = 0.006) and alkaline phosphatase (150 vs 72, P = 0.015) Chronic pancreatitis diagnosis was more frequent in patients with recurrent pancreatitis at baseline (82% vs 21%, P < 0.001). During the follow-up, AP recurred in 3 patients, one of which remained idiopathic. CONCLUSION: EUS is a good test to define AP etiology. It showed a 63% diagnostic gain over CECT + MRCP. In suitable patients, EUS should always be performed in cases of IAP. Further prospective studies are needed.