Hepatic involvement in IgG4-related disease: IgG4-hepatopathy and IgG4-autoimmune hepatitis

Mimickers of immunoglobulin G4-related hepatobiliary disease on biopsy

With the growing recognition of IgG4-related hepatobiliary disease, establishing a definitive diagnosis relies mainly on a combination of clinical findings, serological markers, and imaging modalities. However, the role of histopathological evaluation remains indispensable, particularly in cases necessitating differential diagnosis or malignancy exclusion. While diagnosing IgG4-related hepatobiliary disease through surgical resection specimens is often straightforward, pathologists encounter substantial challenges when evaluating biopsies. The increasing rarity of surgical interventions exacerbates this due to improved disease recognition and suspicion. Numerous confounding factors, including the absence of the characteristic histologic features, limited tissue sample size, biopsy artifacts, and the limited value of IgG4 counts, further complicate the diagnostic process. Additionally, many other disorders exhibit clinical and histological features that overlap with IgG4-related disease, intensifying the complexity of interpreting biopsy specimens. This article explores the clinical and histomorphologic features of IgG4-related hepatobiliary disease and its potential mimickers. It offers valuable insights for pathologists and clinicians when confronted with biopsy specimens from hepatobiliary organs.

Pediatric IgG4-related disease: a descriptive review

INTRODUCTION

IgG4-related disease (IgG4-RD) is an immune-mediated systemic fibroinflammatory condition characterized by serum IgG4 elevation and IgG4-positive plasma cell infiltration into various organs. It generally occurs in elderly males. Pediatric cases have been reported, albeit rarely, accordingly lack of recognition of such cases could delay therapeutic intervention leading to poorer outcomes.

AREAS COVERED

The present review is a descriptive review of all published case reports, cohort studies, and reviews of pediatric IgG4-RD listed in PubMed. Characteristics of pediatric IgG4-RD were clarified, including sex, organ involvement, serological and histological findings, and treatment. We assessed how many published cases met current classification and comprehensive diagnostic criteria.

EXPERT OPINION

The characteristics of pediatricIgG4-RD differed from adult IgG4-RD in terms of sex and involved organs. There was no clear male dominance in numbers of cases, and surface organ involvement such as ophthalmic diseases were more common in the pediatric IgG4-RD. Organ involvement tended to be indolent and unilateral, causing difficulty in definitively diagnosing pediatric IgG4-RD. Only about 20% of published cases met IgG4-RD classification or comprehensive diagnostic criteria. Physicians should be careful in diagnosing pediatric IgG4-RD after excluding mimickers. International collaboration toward high-quality evidence to support diagnosis and treatment of pediatric IgG4-RD is advised.

Immunoglobulin G4-related hepatobiliary disease

Immunoglobuline G4-related disease (IgG4-RD) is a systemic disease that can involve virtually any organs including the biliary tract and liver. The biliary tract involvement of IgG4-RD is known as IgG4-sclerosing cholangitis (IgG4-SC) and may or may not present with an inflammatory pseudotumor. Large bile ducts such as extrahepatic, hilar, and perihilar ducts are typically affected and demonstrate marked bile duct wall thickening and develop strictures. Histologically, the involved ducts show transmural dense lymphoplasmacytic infiltrates with storiform fibrosis extending into peribiliary glands and periductal soft tissue. The luminal epithelium is usually preserved. Tissue eosinophilia and obliterative phlebitis are also frequently noted. Liver biopsy findings of IgG4-SC are heterogeneous and rather nonspecific, but two features specific to IgG4-SC have been described: >10 IgG4-positive plasma cell/HPF and small portal-based fibroinflammatory nodules. Secondary changes, due to downstream bile duct obstruction are often appreciated. When considering the differential diagnosis, primary sclerosing cholangitis and cholangiocarcinoma are great clinical and histologic mimics of IgG4-SC. Liver involvement in IgG4-RD has not been well characterized and includes IgG4-hepatopathy and IgG4-related autoimmune hepatitis (AIH). IgG4-hepatopathy is a generic term covering hepatic lesions related to IgG4-RD and /or IgG4-SC. It includes primary liver parenchymal changes inherent to IgG4-RD, liver parenchymal involvement of IgG4-SC, and secondary changes related to IgG4-SC. IgG4-related AIH is characterized by clinical and histologic features of classical AIH but with prominent (>10/HPF) IgG4-positive plasma cells. It is unclear whether this represents a hepatic manifestation of IgG4-RD or a subset of AIH with increased IgG4-positive plasma cells at the present time. Synchronous or metachronous involvement of other organs, offers a clue to make this distinction. IgG4 immunohistochemistry has an important role in diagnosing IgG4-RD. But the diagnosis cannot be made solely based on the number of IgG4-positive plasma cells, and results need to be interpreted with caution as increased IgG4-positive plasma cells can be seen in other inflammatory conditions or even in malignancy.

The changing faces of IgG4-related disease: Clinical manifestations and pathogenesis

Since the earliest reports in 2001, immunoglobulin G4 (IgG4)-related disease has been defined as an autoimmune systemic disease characterized by the lymphoplasmacytic infiltration of affected tissues leading to fibrosis and obliterative phlebitis along with elevated serum IgG4 levels. Prior to this unifying hypothesis, a plethora of clinical manifestations were considered as separate entities despite the similar laboratory profile. The pathology can be observed in virtually all organs and may thus be a challenging diagnosis, especially when the adequate clinical suspicion is not present or when obtaining a tissue biopsy is not feasible. Nonetheless, the most frequently involved organs are the pancreas and exocrine glands but these may be spared. Immunosuppressants lead to a prompt clinical response in virtually all cases and prevent histological sequelae and, as a consequence, an early differential diagnosis from other conditions, particularly infections and cancer, as well as an early treatment should be pursued. We describe herein two cases in which atypical disease manifestations were observed, i.e., one with recurrent neck lymph node enlargement and proptosis, and one with jaundice. Our understanding of the pathogenesis of IgG4-related disease is largely incomplete but data support a significant role for Th2 cytokines with the contribution of innate immunity factors such as Toll-like receptors, macrophages and basophils. Further, macrophages activated by IL4 overexpress B cell activating factors and contribute to chronic inflammation and the development of fibrosis. We cannot rule out the possibility that the largely variable disease phenotypes reflect different pathogenetic mechanisms and the tissue microenvironment may then contribute to the organ involvement.