Review of the diagnosis,classification and management of autoimmune pancreatitis

Autoimmune pancreatitis(AIP)is a rare form of chronic pancreatitis,with as yet undetermined incidence and prevalence in the general population.Our understanding of it continues to evolve.In the last few years,2separate subtypes have been identified:type 1 AIP has been recognised as the pancreatic manifestation of a multiorgan disease,named immunoglobulin G4(IgG4)-related disease while type 2 AIP is a pancreas specific disorder not associated with IgG4.International criteria for the diagnosis of AIP have been defined:the HISORt criteria from the Mayo clinic,the Japan consensus criteria and,most recently,the international association of pancreatology"International Consensus Diagnostic Criteria".Despite this,in clinical practice it can still be very difficult to confirm the diagnosis and differenti-ate AIP from a pancreatic cancer.There are no large studies into the long-term prognosis and management of relapses of AIP,and there is even less information at present regarding the Type 2 AIP subtype.Further studies are necessary to clarify the pathogenesis,treatment and long-term outcomes of this disease.Critically for clinicians,making the correct diagnosis and differentiating the disease from pancreatic cancer is of the utmost importance and the greatest challenge.     

Reactive fibroinflammatory pseudotumor of the pancreas: report of three cases

Reactive fibroinflammatory pseudotumor located in the pancreas is a rare condition. However, we experienced three cases of reactive fibroinflammatory pseudotumor of the pancreas over the previous 2 years. Immunohistochemical staining of immunoglobulin G4 (IgG4) confirmed that Cases 1 and 3 involved IgG4-related disease and that Case 2 did not. In Cases 1 and 3, the masses were formed through autoimmune reaction and were diagnosed as autoimmune pancreatitis (AIP). In Case 2, because only a few IgG4-positive cells were found, it was difficult to diagnose AIP or IgG4-related disease. Reactive fibroinflammatory pseudotumors can develop without the involvement of any autoimmune mechanisms. There seems to be partial overlap between reactive fibroinflammatory pseudotumors and AIP.     

Autoimmune pancreatitis: proposal of IgG4-related sclerosing disease

Autoimmune pancreatitis (AIP) is a peculiar type of pancreatitis of presumed autoimmune etiology. Many new clinical aspects of AIP have been clarified during the past 10 years, and AIP has become a distinct entity recognized worldwide. However, its precise pathogenesis or pathophysiology remains unclear. As AIP dramatically responds to steroid therapy, accurate diagnosis of AIP is necessary to avoid unnecessary surgery. Characteristic dense lymphoplasmacytic infiltration and fibrosis in the pancreas may prove to be the gold standard for diagnosis of AIP. However, since it is difficult to obtain sufficient pancreatic tissue, AIP should be diagnosed currently based on the characteristic radiological findings (irregular narrowing of the main pancreatic duct and enlargement of the pancreas) in combination with serological findings (elevation of serum γ-globulin, IgG, or IgG4, along with the presence of autoantibodies), clinical findings (elderly male preponderance, fluctuating obstructive jaundice without pain, occasional extrapancreatic lesions, and favorable response to steroid therapy), and histopathological findings (dense infiltration of IgG4-positive plasma cells and T lymphocytes with fibrosis and obliterative phlebitis in various organs). It is apparent that elevation of serum IgG4 levels and infiltration of abundant IgG4-positive plasma cells into various organs are rather specific to AIP patients. We propose a new clinicopathological entity, “IgG4-related sclerosing disease”, and suggest that AIP is a pancreatic lesion reflecting this systemic disease.     

Strategy to differentiate autoimmune pancreatitis from pancreas cancer

Autoimmune pancreatitis (AIP) is a newly described entity of pancreatitis in which the pathogenesis appears to involve autoimmune mechanisms. Based on histological and immunohistochemical examinations of various organs of AIP patients, AIP appears to be a pancreatic lesion reflecting a systemic "IgG4-related sclerosing disease". Clinically, AIP patients and patients with pancreatic cancer share many features, such as preponderance of elderly males, frequent initial symptom of painless jaundice, development of new-onset diabetes mellitus, and elevated levels of serum tumor markers. It is of uppermost importance not to misdiagnose AIP as pancreatic cancer. Since there is currently no diagnostic serological marker for AIP, and approach to the pancreas for histological examination is generally difficult, AIP is diagnosed using a combination of clinical, serological, morphological, and histopathological features. Findings suggesting AIP rather than pancreatic cancer include: fluctuating obstructive jaundice; elevated serum IgG4 levels; diffuse enlargement of the pancreas; delayed enhancement of the enlarged pancreas and presence of a capsule-like rim on dynamic computed tomography; low apparent diffusion coefficient values on diffusion-weighted magnetic resonance image; irregular narrowing of the main pancreatic duct on endoscopic retrograde cholangiopancreatography; less upstream dilatation of the main pancreatic duct on magnetic resonance cholangiopancreatography, presence of other organ involvement such as bilateral salivary gland swelling, retroperitoneal fibrosis and hilar or intrahepatic sclerosing cholangitis; negative work-up for malignancy including endoscopic ultrasound-guided fine needle aspiration; and steroid responsiveness. Since AIP responds dramatically to steroid therapy, accurate diagnosis of AIP can avoid unnecessary laparotomy or pancreatic resection.     

Autoimmune Pankreatitis – Behandlung und Problematik der Diagnosestellung

Background

Autoimmune pancreatitis (AIP) was first classified as a defined disease entity in 1995. It accounts for approximately 2?% of cases of chronic pancreatitis (western world prevalence 36–41/100,000 inhabitants) and AIP is diagnosed in 2.4?% of pancreas resection specimens.

Objectives

Presentation of strategies for diagnosis and treatment with focus on differentiation of AIP and pancreatic carcinoma.

Methods

Selective literature research in PubMed regarding pathogenesis, diagnosis and treatment of AIP.

Results

Key characteristics of AIP are recurrent jaundice due to obstructed bile ducts, histological evidence of fibrosis, a lymphoplasmocytic or granulocytic infiltrate and the response to steroid therapy. There are two distinctive forms of AIP: type I or lymphoplasmocytic sclerosing pancreatitis and type II or idiopathic duct centric pancreatitis. The IgG4 positive AIP type I belongs to the group of IgG4-related systemic diseases. Diagnosis of AIP is established according to the international consensus diagnostic criteria (ICDC) or HISORt (mnemonic standing for histology, imaging, serology, other organ involvement and response to therapy) criteria. Differentiation from pancreatic adenocarcinoma can be challenging. The standard treatment consists of corticosteroids and in some cases azathioprine can be added. In refractory disease rituximab is a further option. Treatment is indicated in patients with jaundice, systemic manifestation or persistent pain.

Conclusion

Although AIP is increasingly being identified, the differentiation from pancreatic adenocarcinoma still remains difficult and in cases of a suspicion of neoplasia, resection should be favored. It can successfully be treated conservatively with steroids and rituximab.     

Clinical and pathophysiological issues associated with type 1 autoimmune pancreatitis

In 1995, Yoshida and colleagues proposed the concept of ‘autoimmune pancreatitis’ (AIP). Recently, it is accepted that the existence of two subtypes of AIP—type 1, which involves immunoglobulin G4 (IgG4) as the pancreatic manifestation of IgG4-related disease (IgG4-RD), and type 2, which is characterized by granulocytic epithelial lesions. Type 2 AIP is thought to be rare in Japan. In 2011, the International Consensus Diagnostic Criteria (ICDC) for autoimmune pancreatitis was proposed. In Japan, the clinical diagnostic criteria of AIP 2011 was proposed by the Japan Pancreas Society (JPS) and the Research Committee of Intractable Diseases of the Pancreas. The JPS 2011 is based on ICDC and a simplified checklist of items to diagnose type 1 AIP. Although recent progress in type 1 AIP has resolved clinical features, diagnosis, treatment, and pathogenesis, many clinical and basic issues still remain unclear. Here, we provide an overview of the recent clinical and basic issues associated with type 1 AIP.     

Autoimmune pancreatitis in the context of IgG4-related disease: Review of imaging findings

Current understanding of autoimmune pancreatitis (AIP) recognizes a histopathological subtype of the disease to fall within the spectrum of IgG4-related disease. Along with clinical, laboratory, and histopathological data, imaging plays an important role in the diagnosis and management of AIP, and more broadly, within the spectrum of IgG4-related disease. In addition to the defined role of imaging in consensus diagnostic protocols, an array of imaging modalities can provide complementary data to address specific clinical concerns. These include contrast-enhanced computed tomography (CT) and magnetic resonance (MR) imaging for pancreatic parenchymal lesion localization and characterization, endoscopic retrograde and magnetic resonance cholangiopancreatography (ERCP and MRCP) to assess for duct involvement, and more recently, positron emission tomography (PET) imaging to assess for extra-pancreatic sites of involvement. While the imaging appearance of AIP varies widely, certain imaging features are more likely to represent AIP than alternate diagnoses, such as pancreatic cancer. While nonspecific, imaging findings which favor a diagnosis of AIP rather than pancreatic cancer include: delayed enhancement of affected pancreas, mild dilatation of the main pancreatic duct over a long segment, the “capsule” and “penetrating duct” signs, and responsiveness to corticosteroid therapy. Systemic, extra-pancreatic sites of involvement are also often seen in AIP and IgG4-related disease, and typically respond to corticosteroid therapy. Imaging by CT, MR, and PET also play a role in the diagnosis and monitoring after treatment of involved sites.     

Autoimmune pancreatitis and cholangitis

Autoimmune pancreatitis(AIP) is part of a systemic fibrosclerotic process characterized by lymphoplasmacytic infiltrate with immunoglobulin G subtype-4(Ig G4) positive cells. It characteristically presents with biliary obstruction due to mass-like swelling of the pancreas. Frequently AIP is accompanied by extra-pancreaticmanifestations including retroperitoneal fibrosis, thyroid disease, and salivary gland involvement. Auto-antibodies, hypergammaglobulemia, and prompt resolution of pancreatic and extrapancreatic findings with steroids signify its autoimmune nature. Refractory cases are responsive to immunomodulators and rituximab. Involvement of the biliary tree, termed IgG 4 associated cholangiopathy, mimics primary sclerosing cholangitis and is challenging to manage. High IgG 4 levels and swelling of the pancreas with a diminutive pancreatic duct are suggestive of autoimmune pancreatitis. Given similarities in presentation but radical differences in management and outcome, differentiation from pancreatic malignancy is of paramount importance. There is controversy regarding the optimal diagnostic criterion and steroid trials to make the diagnosis. Additionally, the retroperitoneal location of the pancreas and requirement for histologic sampling, makes tissue acquisition challenging. Recently, a second type of autoimmune pancreatitis has been recognized with similar clinical presentation and steroid response though different histology, serologic, and extrapancreatic findings.     

Recent advances in the concept and diagnosis of autoimmune pancreatitis and IgG4-related disease

Recent studies have suggested the existence of two subtypes of autoimmune pancreatitis (AIP): type 1 AIP, related to IgG4 (lymphoplasmacytic sclerosing pancreatitis); and type 2 AIP, related to a granulocytic epithelial lesion (idiopathic duct-centric chronic pancreatitis). Compared with type 2 AIP, the clinicopathological features of type 1 AIP, with increased serum IgG4/IgE levels, abundant infiltration of IgG4 + plasmacytes and lymphocytes, autoantibodies, and steroid responsiveness, are more suggestive of abnormal immunity such as allergy or autoimmunity. Moreover, patients with type 1 AIP often have extrapancreatic lesions, such as sclerosing cholangitis, sclerosing sialadenitis, or retroperitoneal fibrosis, showing pathological features similar to those of the pancreatic lesions. Based on these findings, an international concept of and diagnostic criteria for AIP have been proposed recently. Of interest, many synonyms have been proposed for the conditions of AIP and extrapancreatic lesions associated with IgG4, such as "multifocal idiopathic fibrosclerosis," "IgG4-related autoimmune disease," "IgG4-related sclerosing disease," "systemic IgG4-related plasmacytic syndrome (SIPS)," and "IgG4-related multiorgan lymphoproliferative syndrome," all of which may refer to the same conditions. Therefore, the Japanese Research Committee for "Systemic IgG4-Related Sclerosing Disease" proposed a disease concept and clinical diagnostic criteria based on the concept of multifocal fibrosclerosing disease, in 2009, in which the term "IgG4-related disease" was agreed upon as a minimal consensus to cover these conditions. Although the significance of IgG4 in the development of "IgG4-related disease" remains unclear, we have proposed a hypothesis for the development of type 1 AIP, one of the IgG4-related diseases. The concept and diagnostic criteria of "IgG4-related disease" will be changed in accordance with future studies.     

Pathophysiology of autoimmune pancreatitis简

Autoimmune pancreatitis (AIP) is a recently discovered form of pancreatitis and represents one of the diseases of the pancreas which can be cured and healed medically. International consensus diagnostic criteria have been developed, and the clinical phenotypes associated with the histopathologic patterns of lymphoplasmacytic sclerosing pancreatitis and idiopathic duct-centric pancreatitis should be referred to as type 1 and type 2 AIP, respectively. Most importantly, in type 1 AIP, the pancreatic manifestations are associated with other extrapancreatic disorders, resembling an immunoglobulin G4 (IgG4)-related disease. In addition, the pancreas of a patient with AIP is often infiltrated by various types of immune cells; the cluster of differentiation (CD) 4 or CD8 T lymphocytes and IgG4-bearing plasma cells have been found in the pancreatic parenchyma and other involved organs in AIP and factors regulating T-cell function may influence the development of AIP. From a genetic point of view, it has also been reported that DRB1*0405 and DQB1*0401 mutations are significantly more frequent in patients with AIP when compared to those with chronic calcifying pancreatitis, and that only DQB1*0302 had a significant association with the relapse of AIP. Finally, it has been found that the polymorphic genes encoding cytotoxic T lymphocyte-associated antigen 4, a key negative regulator of the T-cell immune response, are associated with AIP in a Chinese population. Even if these data are not concordant, it is possible that physiological IgG4 responses are induced by prolonged antigen exposure and controlled by type 2 helper T cells. We reviewed the current concepts regarding the pathophysiology of this intriguing disease, focusing on the importance of the humoral and cellular immune responses.     

Pathophysiology of autoimmune pancreatitis

Autoimmune pancreatitis(AIP) is a recently discovered form of pancreatitis and represents one of the diseases of the pancreas which can be cured and healed medically. International consensus diagnostic criteria have been developed, and the clinical phenotypes associated with the histopathologic patterns of lymphoplasmacytic sclerosing pancreatitis and idiopathic duct-centric pancreatitis should be referred to as type 1 and type 2AIP, respectively. Most importantly, in type 1 AIP, the pancreatic manifestations are associated with other extrapancreatic disorders, resembling an immunoglobulin G4(IgG4)-related disease. In addition, the pancreas o a patient with AIP is often infiltrated by various types of immune cells; the cluster of differentiation(CD) 4or CD8 T lymphocytes and IgG4-bearing plasma cells have been found in the pancreatic parenchyma and other involved organs in AIP and factors regulating T-cell function may influence the development of AIP From a genetic point of view, it has also been reported that DRB1*0405 and DQB1*0401 mutations are significantly more frequent in patients with AIP when compared to those with chronic calcifying pancreatitis, and that only DQB1*0302 had a significant association with the relapse of AIP. Finally, it has been found that thepolymorphic genes encoding cytotoxic T lymphocyteassociated antigen 4, a key negative regulator of the T-cell immune response, are associated with AIP in a Chinese population. Even if these data are not concordant, it is possible that physiological IgG4 responses are induced by prolonged antigen exposure and controlled by type 2 helper T cells. We reviewed the current concepts regarding the pathophysiology of this intriguing disease, focusing on the importance of the humoral and cellular immune responses.     

Localized Autoimmune Pancreatitis: Report of a Case Clinically Mimicking Pancreatic Cancer and a Literature Review

Autoimmune pancreatitis (AIP) is a rare disease with clinical presentations that greatly mimic pancreatic cancer (PC). It is critical for clinicians to distinguish AIP from PC because their treatments and prognoses are entirely different. Typical images show characteristic features such as diffuse pancreatic swelling and strictures of the main pancreatic duct (MPD). However, AIP may present as a localized pancreatic mass, in which case it is very difficult to differentiate from PC. Here, we report a case of a 40-year-old man with computed tomography (CT) imaging studies confirming an area of low-density neoplasm in the uncinate process of the pancreas with dilation in the common biliary duct (CBD) and MPD. Increased uptake in the uncinate mass was observed by positron emission tomography (PET)/CT scan, which strongly suggested PC. Further laboratory analyses showed a marked elevation of serum IgG4. Because there was not enough evidence to rule out a diagnosis of malignancy, a histopathological biopsy became the criterion standard. An endoscopic ultrasound (EUS)-guided needle biopsy failed. As an alternative, a pancreaticoduodenectomy was conducted for the biopsy, and pathological analysis confirmed IgG4-related sclerotic chronic pancreatitis with moderate lymphoplasmacellular infiltration.We suggest that an accurate preoperative diagnosis for localized AIP with MPD and CBD obstructions mimicking PC is of great importance. Radiological imaging findings, particularly observations of diffused enlargement of the pancreas and delayed enhancement during the venous and portal phases, are essential for diagnosing AIP. Careful consideration should be given if serum IgG4 was taken as a special indicator for a differential diagnosis between AIP and PC. A history of IgG4-related diseases involving the biliary, lacrimal, salivary, retroperitoneal, renal, or pulmonary systems should also be highlighted. Thus, the pathology of extrapancreatic organs can be utilized as diagnostic evidence when the pathology for a pancreatic mass is not available, as in the case presented here. Furthermore, cautious use of hormone therapy is indicated for patients who cannot be ruled out as having PC. The results of future studies on localized AIP are eagerly awaited.     

IgG4-related sclerosing disease

Based on histological and immunohistochemical exami- nation of various organs of patients with autoimmune pancreatitis （AIP）, a novel clinicopathological entity of IgG4-related sclerosing disease has been proposed. This is a systemic disease that is characterized by extensive IgG4-positive plasma cells and T-lymphocyte infiltration of various organs. Clinical manifestations are apparent in the pancreas, bile duct, gallbladder, salivary gland, retroperitoneum, kidney, lung, and prosrate, in which tissue fibrosis with obliterative phlebitis is pathologically induced. AlP is not simply pancreatitis but, in fact, is a pancreatic disease indicative of IgG4- related sclerosing diseases. This disease includes AlP, sclerosing cholangitis, cholecystitis, sialadenitis, retro-peritoneal fibrosis, tubulointerstitial nephritis, interstitial pneumonia, prostatitis, inflammatory pseudotumor and lymphadenopathy, all IgG4-related. Most IgG4-related sclerosing diseases have been found to be associated with AlP, but also those without pancreatic involvement have been reported. In some cases, only one or two organs are clinically involved, while in others, three or four organs are affected. The disease occurs predominantly in older men and responds well to steroid therapy. Serum IgG4 levels and immunos-taining with anti-IgG4 antibody are useful in making the diagnosis. Since malignant tumors are frequently suspected on initial presentation, IgG4-related sclerosing disease should be considered in the differential diagnosis to avoid unnecessary surgery.     

Autoimmune pancreatitis

Autoimmune pancreatitis (AIP) is a benign, IgG4-related, fibroinflammatory form of chronic pancreatitis that can mimic pancreatic ductal adenocarcinoma both clinically and radiographically. Laboratory studies typically demonstrate elevated serum IgG4 levels and imaging studies reveal a diffusely or focally enlarged pancreas with associated diffuse or focal narrowing of the pancreatic duct. The pathologic features include periductal lymphoplasmacytic inflammation, obliterative phlebitis, and abundant IgG4-positive plasma cells. The treatment of choice for AIP is steroid therapy. Diagnostic criteria for AIP have been proposed that incorporate histologic, radiographic, serologic, and clinical information.     

Diagnosis of autoimmune pancreatitis

Autoimmune pancreatitis(AIP) is a distinct form of chronic pancreatitis that is increasingly being reported. The presentation and clinical image findings of AIP sometimes resemble those of several pancreatic malignancies, but the therapeutic strategy differs appreciably. Therefore, accurate diagnosis is necessary for cases of AIP. To date, AIP is classified into two distinct subtypes from the viewpoints of etiology, serum markers, histology, other organ involvements, and frequency of relapse: type 1 is related to Ig G4(lymphoplasmacytic sclerosing pancreatitis) and type 2 is related to a granulocytic epithelial lesion(idiopathic duct-centric chronic pancreatitis). Both types of AIP are characterized by focal or diffuse pancreatic enlargement accompanied with a narrowing of the main pancreatic duct, and both show dramatic responses to corticosteroid. Unlike type 2, type 1 is characteristically associated with increasing levels of serum Ig G4 and positive serum autoantibodies, abundant infiltration of Ig G4-positive plasmacytes, frequent extrapancreatic lesions, and relapse. These findings have led several countries to propose diagnostic criteria for AIP, which consist of essentially similar diagnostic items; however, several differences exist for each country, mainly due to differences in the definition of AIP and the modalities used to diagnose this disease. An attempt to unite the diagnostic criteria worldwide was made with the publication in 2011 of the international consensus diagnostic criteria for AIP, established at the 2010 Congress of the International Association of Pancreatology(IAP).     

Misdiagnosis and delayed diagnosis of atypical autoimmune pancreatitis: Experience from clinical cases

Autoimmune pancreatitis (AIP) is a fibro-inflammatory disease characterized by inflammation and fibrosis of the pancreas. It is a systemic disease that can affect multiple organs, including the bile ducts, kidneys, lungs, and other organs. However, due to its complex presentation, AIP is often challenging to diagnose, and misdiagnosis with pancreatic tumors can occur. In our study, we reviewed three cases of atypical AIP where patients had normal serum IgG4 levels, leading to initial misdiagnosis with pancreatic tumors. Delayed diagnosis resulted in irreversible pathologies such as retroperitoneal fibrosis. All three patients had bile duct involvement, and imaging findings were similar to those of tumors, further complicating the diagnosis. The correct diagnosis was confirmed only after diagnostic therapy. Our study aims to raise awareness of atypical AIP and improve diagnostic efficiency by analyzing the clinical characteristics of these patients.     

I型自身免疫性胰腺炎的研究进展

自身免疫性胰腺炎（AIP）是逐渐被认识的慢性胰腺炎的一种类型,与其他类型的慢性胰腺炎有明显的不同。随着2001年发现AIP患者血清IgG4含量明显增高,这个现实被广泛的接受。1型AIP与2型AIP不同。2％的慢性胰腺炎为1一AIP,成人男性患者居多。患者通常由于胰头的增大或胆管壁增厚所致梗阻性黄疸,通过血清学、影像学和组织学与胰腺癌鉴别。血清IgG4水平的增高是最为敏感和特异性的表现。影像学的表现为胰管的不规则狭窄,胰腺弥散性或局灶性的扩大及胰周可见环形的囊壳样影,以及影像延迟期强化。组织学显示大量的dxDt问质表现为致密的纤维化伴席纹状、炎细胞浸润,闭塞性静脉炎和lgG4阳性细胞数量增加。激素治疗疗效明显是另外的特征,在初治的2～3周血清学和影像学明显改善。基于同步或不同步的伴有多器官的损伤,1一AIP也被认为是一种IgG4相关全身性疾病。至今有一些与1一AIP相关的自身免疫性抗原被鉴定,但IgG4在此病中的作用是肯定的。     

First case of IgG4-related sclerosing cholangitis associated with autoimmune hemolytic anemia

To our knowledge, patients with immunoglobulin G4-related sclerosing cholangitis (IgG4-SC) associated with autoimmune hemolytic anemia (AIHA) have not been reported previously. Many patients with IgG4-SC have autoimmune pancreatitis (AIP) and respond to steroid treatment. However, isolated cases of IgG4-SC are difficult to diagnose. We describe our experience with a patient who had IgG4-SC without AIP in whom the presence of AIHA led to diagnosis. The patient was a 73-year-old man who was being treated for dementia. Liver dysfunction was diagnosed on blood tests at another hospital. Imaging studies suggested the presence of carcinoma of the hepatic hilus and primary sclerosing cholangitis, but a rapidly progressing anemia developed simultaneously. After the diagnosis of AIHA, steroid treatment was begun, and the biliary stricture improved. IgG4-SC without AIP was thus diagnosed.     

Autoimmune pancreatitis

The purpose of this review is to provide a concise view of the existing knowledge of autoimmune pancreatitis (AIP) for practicing clinicians. AIP is a rare disease whose recognition and understanding are evolving. It is a type of chronic pancreatitis that often presents as obstructive jaundice, has a distinctive histology, and is exquisitely sensitive to steroid therapy. This form of chronic pancreatitis has a unique clinical, biochemical, and radiological profile. The term "AIP" encompasses two subtypes: types 1 and 2. Type 1 AIP is the pancreatic manifestation of a systemic fibro-inflammatory disease called immunoglobulin G4-associated systemic diseases. Type 2 AIP has been shown to be associated with inflammatory bowel disease. Existing criteria are geared towards the diagnosis of type 1 AIP. At present, pancreatic histology is a requirement for the definitive diagnosis of type 2 AIP. AIP can mimic most other pancreatic diseases in its presentation, but in clinical practice, it often has to be differentiated from pancreatic cancer. There are established criteria and algorithms not only to diagnose AIP, but also to differentiate it from pancreatic cancer. The utility of these algorithms and the approach to management are discussed here.     

Recent Advances in the Concept and Pathogenesis of IgG4-Related Disease in the Hepato-Bilio-Pancreatic System

Recent studies have proposed nomenclatures of type 1 autoimmune pancreatitis (AIP) (IgG4-related pancreatitis), IgG4-related sclerosing cholangitis (IgG4-SC), IgG4-related cholecystitis, and IgG4-related hepatopathy as IgG4-related disease (IgG4-RD) in the hepato-bilio-pancreatic system. In IgG4-related hepatopathy, a novel concept of IgG4-related autoimmune hepatitis (AIH) with the same histopathological features as AIH has been proposed. Among organs involved in IgG4-RD, associations with pancreatic and biliary lesions are most frequently observed, supporting the novel concept of “biliary diseases with pancreatic counterparts.” Targets of type 1 AIP and IgG4-SC may be periductal glands around the bile and pancreatic ducts. Based on genetic backgrounds, innate and acquired immunity, Th2-dominant immune status, regulatory T (Treg) or B cells, and complement activation via a classical pathway may be involved in the development of IgG4-RD. Although the role of IgG4 remains unclear in IgG4-RD, IgG4-production is upregulated by interleukin 10 from Treg cells and by B cell activating factor from monocytes/basophils with stimulation of toll-like receptors/nucleotide-binding oligomerization domain-like receptors. Based on these findings, we have proposed a hypothesis for the development of IgG4-RD in the hepato-bilio-pancreatic system. Further studies are necessary to clarify the pathogenic mechanism of IgG4-RD.