Clinical Characteristics and Prognosis of Idiopathic Acute Pancreatitis.

Objective: Acute pancreatitis is a serious diagnosis with an increasing incidence in the Western world. In this study we sought to investigate the incidence of idiopathic AP and to compare clinical and prognostic characteristics of idiopathic cases with cases of AP with known etiology.

Methods: In this retrospective study of adult hospitalized patients diagnosed with acute pancreatitis between 2012 and 2015, a comparison was made between admissions of patients with known etiology and those for whom no cause was found. Primary outcome was defined as composite outcome of 30-day mortality and complications.

Results: Among 560 admissions of 437 patients with a primary diagnosis of acute pancreatitis, the main factors identified were gallstones (51.2%) and idiopathic pancreatitis (35.9%), with alcohol ranked third at only 4.8%. Mortality rate within 30 days of hospitalization was 2.9% and within one year was 7.1%. Use of lipid-lowering, anti-hypertensive, and anti-diabetic medications was more frequent among patients with "idiopathic" disease (70%, 68%, and 33% versus 59%, 56%, and 27%, respectively). Patients admitted with idiopathic AP, in comparison to patients with known AP etiology, had milder disease with shorter hospital stay (3 days versus 4, respectively), and less re-admission in 30 days (7.5% versus 21.2%). Idiopathic AP patients had better prognosis in terms of 30-day death and complication (HR 0.33, 95% CI 0.08-0.40, P<0.001).

Conclusion: Idiopathic disease is common among acute pancreatitis patients; the two study groups differed in severity of disease and prognosis. Common use of medications with doubtful value suggests possible under-diagnosis of drug-induced acute idiopathic pancreatitis.