Autoimmune pancreatitis (AIP) is frequently associated with involvement of several extrapancreatic organs. This recognition has led to the concept of IgG4-related disease, of which the pancreatic manifestation is type 1 AIP. IgG4-positive lymphoplasmacytic infiltrate and characteristic pattern of fibrosis (storiform fibrosis) are seen in the involved organs. Bile duct and lymph nodes are commonly involved in AIP. Additionally, involvements of retroperitoneum, kidneys, lungs, liver, salivary and lacrimal glands, prostate, and thyroid have been well characterized. The spectrum of organs involved in IgG4-related disease continues to grow with increasing awareness of the disease, and recently a systematic nomenclature has been proposed. Diagnosis of involvement of other organs in AIP is based on symptoms, clinical exam, radiologic review, and often histology. While manifestations in the involved organs mimic other organ-specific diseases, a dramatic response to steroids is characteristic. Recognition of other organ involvement has significance for diagnosis of AIP and is incorporated in the diagnostic criteria for AIP.
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