Diagnosis of idiopathic acute pancreatitis: the simpler, the better?

Acute pancreatitis continues to be one of the most common gastrointestinal (GI) conditions requiring hospitalization. The term “idiopathic acute pancreatitis” (IAP) is used when the most common causes of acute pancreatitis, like alcohol and gallstones, have been ruled out, with there also being no discernible etiology after extensive evaluation of patient history, physical examination, laboratory tests, and conventional imaging studies [1] [2]. Transabdominal ultrasound and computed tomography (CT) are the usual initial imaging modalities and are indicated after causes such as drugs, infections, genetic mutations, and metabolic disorders, such as hypercalcemia and hypertriglyceridemia, have been ruled out. A second ultrasound scan sometimes finds a biliary cause, in around 20 % of patients diagnosed as IAP, if the first one was unrevealing [3].

Despite the above work-up, an etiology is not established in approximately 10 % – 30 % of acute pancreatitis cases [4]. In such cases, current recommendations suggest at least two GI imaging techniques be performed that include endoscopic ultrasonography (EUS) and magnetic resonance cholangiopancreatography (MRCP) to further evaluate a cause for the acute pancreatitis [1] [2]. Undetected microlithiasis and/or biliary sludge has been considered as one of the major undiagnosed causes of IAP accounting for 30 % – 80 % of cases. Other causes that could potentially be diagnosed by GI imaging modalities are pancreas divisum, sphincter of Oddi dysfunction, a choledochocele, an anomalous pancreaticobiliary junction, an annular pancreas, and pancreatic and/or ampullary neoplasms [1] [2].

From an emerging modality over the past many years, EUS has established its role as an efficient diagnostic tool in various pancreatic disorders, ranging from simple cysts to complicated chronic pancreatitis. EUS has demonstrated accuracy of up to 80 % in ascertaining a cause in patients with IAP, especially in the diagnosis of gallbladder microlithiasis and/or sludge [5]; however, its overall performance as an effective diagnostic tool in IAP has been limited by a lack of robust data. A previous meta-analysis evaluated the diagnostic yields of EUS, MRCP, and secretin-stimulation MRCP (S-MRCP) [5]. The authors, Wan et al., concluded that EUS and MRCP should both be used in the diagnostic work-up of IAP as complementary techniques, although EUS resulted in a higher diagnostic yield than MRCP (64 % vs. 34 %) in ascertaining a possible biliary etiology of IAP. The authors also demonstrated that S-MRCP was superior to EUS and MRCP in the diagnosis of possible anatomic alteration of the biliopancreatic duct system. Although limited by differences in the groups compared and heterogeneity, the study provided an early insight into the clinical usefulness of EUS in the diagnostic evaluation of IAP.

“…it seems from the analysis that EUS might yield the best outcomes when done after the acute pancreatitis event has subsided.”

In this edition of Endoscopy, a systematic review and meta-analysis by Umans et al. expands on the clinical yield of EUS in detecting a cause in patients with IAP [6]. The authors set out with a primary goal to determine the diagnostic yield of EUS in ascertaining an etiology in IAP and report an overall yield of 59 %. The majority of IAP patients had a biliary etiology (30 %), followed by chronic pancreatitis in 20 %. Furthermore, the authors demonstrate that episodes of acute pancreatitis before the EUS did not affect the diagnostic yield and in fact the yield was higher when EUS was performed after clinical recovery rather than during the acute episode (61 % vs. 48 %), especially for patients with a gallbladder in situ.

Before acknowledging the results of this meta-analysis, a few limitations need to be noted. One of the most important limitations is that the included studies lacked a complete standard diagnostic work-up of IAP before imaging by EUS. This raises the important question of whether the studied sample were truly IAP as per the current guidelines. As the majority of the causes of IAP diagnosed by EUS were related to biliary microlithiasis and/or biliary sludge, the authors were not able to associate the relationship to liver function tests and pan-abdominal ultrasound results. There seems to be a possibility that the reported rate of 59 % with EUS might be an overestimate in reality. It is understandable that this is no fault of the authors and they do acknowledge that future studies should focus on including homogeneous patients who truly have IAP before EUS is performed.

As a result, one cannot conclude with absolute certainty the appropriate timing of EUS in the diagnostic workflow of IAP based on this study alone. However, it seems from the analysis that EUS might yield the best outcomes when done after the acute pancreatitis event has subsided. The authors also do commendable work in providing the granular data on the etiologies diagnosed by EUS, including pancreatic cancers, which were diagnosed in 2 % of IAP patients [6]. The study does not however put the results in perspective to MRCP and/or S-MRCP, as this was not the scope of the study. Based on prior data and evidence, S-MRCP seems to be the better modality in diagnosing anatomic biliopancreatic abnormalities [5]. Future studies are warranted to establish the comparative performances of S-MRCP and EUS in this regard. Until then, EUS might help detect a cause in the majority of IAP patients and the diagnostic workflow could be simpler and better!

Publication History

Article published online:
27 October 2020

• References

• 1 Guda NM, Trikudanathan G, Freeman ML. Idiopathic recurrent acute pancreatitis. Lancet Gastroenterol Hepatol 2018; 3: 720-728
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• 3 Hallensleben ND, Umans DS, Bouwense S. et al. The diagnostic work-up and outcomes of ‘presumed’ idiopathic acute pancreatitis: A post-hoc analysis of a multicentre observational cohort. United European Gastroenterol J 2020; 8: 340-350
• 4 van Brummelen SE, Venneman NG, van Erpecum KJ. et al. Acute idiopathic pancreatitis: does it really exist or is it a myth?. Scand J Gastroenterol Suppl 2003; 239: 117-122
• 5 Wan J, Ouyang Y, Yu C. et al. Comparison of EUS with MRCP in idiopathic acute pancreatitis: a systematic review and meta-analysis. Gastrointest Endosc 2018; 87: 1180-1188.e9
• 6 Umans D, Rangkuti C, Weiland C. et al. Endoscopic ultrasonography can detect a cause in the majority of patients with idiopathic acute pancreatitis: a systematic review and meta-analysis. Endoscopy 2020; 52: 955-964