[Rational diagnostics and differential diagnosis in IgG4-related disease].

Immunoglobulin G4 (IgG4)-related diseases are a heterogenous group of chronic inflammatory systemic disorders characterized by fibrosing inflammation with infiltration of IgG4-positive plasma cells. They can affect nearly any organ system. Typical manifestations include autoimmune pancreatitis, sclerosing cholangitis, lymphadenopathy, retroperitoneal fibrosis, and inflammatory orbitopathy as well as involvement of the salivary and lacrimal glands. Each manifestation may present in isolation or in combination with others. Diagnosis requires careful exclusion of malignant or other inflammatory conditions, as IgG4-related diseases can mimic a wide range of disease entities. A multimodal approach combining laboratory findings, histopathological evaluation and radiological imaging is essential for establishing the diagnosis. A structured diagnostic algorithm and close interdisciplinary collaboration are crucial to avoid misdiagnosis and enable appropriate treatment.