Pancreaticobiliary involvement in treated type 1 autoimmune pancreatitis: Imaging pattern and risk factors for...

To evaluate the imaging pattern of pancreaticobiliary lesions in patients with treated type 1AIP, to determine the incidence of disease relapse and malignancy, and to identify the risk factors.

The institutional review board approval was acquired. All patients gave written informed consent. From a prospective clinico-radiological database since 2012, consecutive patients with type 1 AIP who were treated and followed up (≥18 months) were identified. The presence/absence of pancreaticobiliary lesion(s) development during follow-up were assessed. The etiology was determined and the imaging pattern was compared to the initial attack. Risk factors were identified by univariate and multivariate analysis.

Among 103 patients with treated type 1 AIP, 44 (42.7%) developed pancreaticobiliary lesions during follow up (median time interval to initial diagnosis: 17 months, range 3-62 months), mostly after steroid discontinuation (63.6%) or during maintenance therapy (29.5%). All lesions were disease relapse, which responded to steroid treatment. At relapse, pancreatic involvement was less frequent (81.8% vs 100%, p = 0.003), and the pancreas size was smaller (p < 0.01), whereas extra-pancreatic bile duct (ExPanBD) involvement was more severe and extensive (both p < 0.01). Multivariate analysis revealed ExPanBD involvement at initial diagnosis (hazard ratio 2.437, 95% CI 1.343-7.402, p = 0.002) and serum IgG4 response ratio at the induction phase (hazard ratio 0.357, 95% CI 0.055-0.804, p = 0.011) as significant independent predictors of relapse.

In treated type 1 AIP, although imaging pattern may differ, pancreaticobiliary lesions are usually manifestations of disease relapse. ExPanBD involvement and poor serum response suggests high risk of relapse.