One important difference in the diagnosis strategy lies in the utility of pancreatic core biopsies. EUS-guided pancreatic core biopsies are routinely performed at our center [63] and have also been routinely done at many other centers in the USA [64]. These are included in the HISORt criteria [28, 36]. In contrary, core biopsies are not performed frequently in Japan and thereby not required in the Asian and Japanese criteria [6, 34].

Another major contention is in the use of ductal imaging (ERP/MRP). The HISORt criteria [28, 36] does not require for ERP/MRP, while the Asian and Japanese criteria require pancreatic duct imaging by ERP/MRP [6, 34]. In the USA, routine ERP/MRP is not performed of obstructive jaundice. The diagnostic utility of ERP from the diagnosis of AIP and differentiating it from pancreatic cancer in the USA was not satisfactory in contrary to that observed in the Japanese centers [65].

The ICDC [40] includes ERP as an additional option which could supplement evidence in favor of AIP to qualify patients for a steroid trial who would otherwise need to be subjected to core biopsy. This is applicable to patients who do not have highly supportive parenchymal imaging and have some collateral evidence (other organ involvement or serum IgG4 elevations) but not sufficient for meeting criteria [40]. In our experience, only 10 % of patients would fall in this category who could be subjected to ductal imaging or core biopsy for diagnosis by ICDC thereby allowing for regional flexibility. About 20 % of patients do not have any collateral evidence and histological diagnosis is mandated in these patients regardless of parenchymal or ductal imaging.

Our protocol for initial steroid treatment is as follows: prednisone 40 mg/day for 4 weeks and tapering off by 5 mg/week to complete a course of 11 weeks. Treatment response is objectively monitored by clinical follow-up, follow-up imaging, and biochemical tests (LFT). Steroid taper is started once response to treatment is confirmed objectively [59, 60].

In our experience, about half of type 1 AIP patients do not relapse after short course of steroid treatment [60]. No maintenance therapy is necessary in these patients [60]. The major difference from Asian strategy is the need for maintenance steroid therapy [66]. Centers in Japan routinely use a prolonged maintenance therapy for up to 3 years with the logic that most patients relapse within 3 years [66]. In a multicenter study from Japan, it was shown that maintenance therapy reduced the relapse rate to 23 % from 34 % in those who weaned off steroids [66]. In our experience, the risks of universal use of maintenance steroid therapy outweigh the benefits in AIP.

Our strategy for follow-up for relapses involves close monitoring of symptoms with radiological and biochemical confirmation of relapse if symptomatic [60]. Early detection of relapses and prompt institution of treatment are recommended. Steroid retreatment with or without immunomodulators, rituximab treatment, and maintenance therapy with these agents may be necessary in 30–40 % of AIP patients with frequent relapses or refractory disease or steroid intolerance [60]. Details of treatment of relapses and maintenance therapy options are discussed extensively in an earlier chapter.