Due to its rarity, little is known about AIP type 2, in contrast to the substantially better-established understanding of AIP type 1, which has evolved considerably over time. Diagnostic criteria of AIP are based on a combination of clinical presentation, serological markers, imaging findings, histology, and response to corticosteroids [3]. Despite these criteria, the diagnosis of AIP-2 remains challenging, largely due to its low prevalence, limited histological sampling, and absence of reliable serum biomarkers.

Except for indistinguishable imaging signs and a well-established respond on steroids, AIP type 2 generally shows different clinical, histologic, and prognostic characteristics from AIP type 1[1]. Clinically, type 2 AIP differs from type 1 in that serum IgG4 levels are typically normal or low, and there is usually no other-organ involvement [1]. However, inflammatory bowel disease (IBD), particularly ulcerative colitis, is associated in approximately 15–45% of cases [5]. This association represents one of the few consistent extra-pancreatic features of type 2 AIP.

Histopathology remains the gold standard for diagnosis. It is characterized by a duct-centric fibro-inflammatory process with neutrophilic infiltration of medium and small pancreatic ducts and the presence of granulocytic epithelial lesions, which represent its most specific histopathological feature [1,5]. However, pancreatic biopsy is not always feasible in clinical practice due to its invasive nature and associated procedural risks. This limitation is particularly relevant in suspected AIP-2, where tissue sampling is often unavailable, further complicating definitive diagnosis.

The absence of reliable serological markers and the limited availability of histological confirmation frequently result in delayed diagnosis, misclassification, or unnecessary surgical intervention. In clinical practice, a probable diagnosis of AIP-2 is often made by integrating imaging findings, steroid responsiveness, and the presence of concomitant IBD when histology is unavailable or non-diagnostic. This pragmatic approach is supported by international consensus recommendations [3].

Radiologically, as seen in our case, focal AIP may demonstrate a range of characteristic findings, including sausage-shaped enlargement, delayed homogeneous enhancement, a capsule-like rim, irregular narrowing of the main pancreatic duct (MPD) and/or common bile duct strictures, and upstream MPD dilation ≤5 mm [6]. Importantly, sausage-shaped enlargement was observed in 11 of 19 focal AIP cases but was not seen in pancreatic cancer, supporting its diagnostic specificity [6]. This imaging feature has been consistently reaffirmed in subsequent studies as a key characteristic of AIP [7].

Corticosteroids remain the cornerstone of therapy for autoimmune pancreatitis. Standard treatment typically consists of oral prednisone at a dose of 40 mg daily for 4–6 weeks, followed by a gradual taper of approximately 5 mg per week over a two-month period, although the optimal duration of therapy and long-term outcomes remain uncertain [8]. In patients with relapse or steroid dependence, rituximab may be considered as an alternative therapeutic option, while steroid-sparing agents such as thiopurines have demonstrated limited efficacy [9].

According to the 2017 International Consensus, indications for steroid therapy include symptomatic pancreatic disease such as obstructive jaundice and abdominal pain, involvement of other organs, and persistent pancreatic masses or systemic manifestations consistent with IgG4-related disease [9]. Treatment is also indicated in patients with progressive disease affecting critical structures, including biliary obstruction, cholangitis, or evidence of irreversible organ damage such as pancreatic exocrine or endocrine insufficiency and hepatobiliary fibrosis. A Japanese study from a long-term follow-up study of 23 patients with AIP concludes that the indications for steroid therapy in AIP are obstructive jaundice due to stenosis of the bile duct or other associated systemic autoimmune diseases, where the presence of diabetes mellitus might be an indication [8].

Despite the general effectiveness of corticosteroids, spontaneous remission has been reported in a subset of patients with AIP, particularly in type 2 disease. AIP-2 is treated less frequently with corticosteroids compared with type 1 disease and demonstrates lower relapse rates (9% and 31%, respectively) [9]. Moreover, remission rates appear similar between treated and untreated patients, suggesting that maintenance therapy may not be necessary in this subgroup [9].

Several studies support the phenomenon of spontaneous remission. Kamisawa et al. [8] reported spontaneous improvement in 3 of 23 patients, while 10 underwent surgical intervention. Notably, 50% of patients treated with corticosteroids developed pancreatic atrophy, highlighting potential treatment-related adverse effects and raising questions about overtreatment in selected cases [8]. Similarly, Kubota et al. [10] reported spontaneous remission in 65% of untreated patients and identified low disease activity and IgG4 seronegativity as independent predictors of spontaneous remission. Additional favorable prognostic factors included the absence of obstructive jaundice or of diabetes mellitus, the lack of duodenal papillary swelling, negative IgG4 staining of the duodenal papilla, and focal pancreatic involvement on imaging. Among additional histological and endoscopic markers, negative IgG4 staining of the duodenal papilla has been proposed as a potential predictor of spontaneous remission. However, its independent predictive value remains limited [10].

Based on current evidence, a conservative “watch-and-wait” approach may be appropriate in selected asymptomatic patients, particularly those without papillary swelling and with favorable imaging features. This strategy is supported by International Consensus guidelines which recommend observational management in carefully selected cases [9].

In the present case, both clinical symptoms and imaging abnormalities resolved completely without pharmacological intervention, as the patient left against medical advice. This spontaneous resolution further supports the recognized benign and reversible nature of type 2 AIP. In contrast to type 1 disease, cross-sectional imaging in type 2 AIP -particularly MRI performed after the acute inflammatory phase- may appear normal, as the inflammatory process is typically duct-centric and does not usually result in significant fibro-inflammatory remodeling. Consequently, structural abnormalities may resolve entirely without residual fibrosis on follow-up imaging. This reflects the generally benign and reversible nature of type 2 AIP and supports the observation that imaging can return to baseline in the absence of chronic fibrotic remodeling [7].