Person:

Sahani, Dushyant

Autoimmune pancreatitis (AIP) is a chronic inflammatory disease of the pancreas. Examination of pancreatic resection specimens from patients with AIP has shown that there are 2 subclasses of this disease. However, there is no widely accepted pathologic classification scheme and the clinical significance of such a classification remains to be established. In this study, we revisited the subclassification of AIP and examine whether this provides clinically and prognostically meaningful information. We evaluated 29 pancreatic resection specimens from patients with AIP. Demographic, clinical, and imaging data were recorded, as was evidence of extrapancreatic manifestations. In addition to a detailed and semiquantitative histologic evaluation, immunohistochemistry for IgG4 was performed on pancreatic and extrapancreatic tissues. We also evaluated 48 consecutive cases of chronic pancreatitis, not otherwise specified. The resected specimens could readily be subclassified into 2 subtypes: type 1 (n=11) and type 2 (n=18). In comparison with patients with type 2 disease, patients with type 1 disease were significantly more likely to be males (P=0.09), older (P=0.02), and present with jaundice (P=0.01), and less likely to be associated with abdominal pain (P=0.04). On imaging, the pancreatic tail cut-off sign was exclusively seen in patients with type 2 disease (4 of 10 cases). Hypercellular inflamed interlobular stroma was unique to type 1 pattern (91%), whereas significant ductal injury in the form of microabscesses and ductal ulceration was almost exclusively seen in type 2 pattern (78%). Eight of 10 patients with a type 1 pattern had evidence of a systemic disease. Three patients with type 2 disease had recurrent episodes of pancreatitis after their pancreatic resection. In comparison with the cohort of chronic pancreatitis, not otherwise specified, type 2 AIP cases were less likely to be associated with a history of alcohol abuse, and showed significantly more foci of periductal inflammation and neutrophilic microabscesses. Our review of pancreatic resection specimens shows 2 histologically distinct forms of AIP. Our data support the concept that type 1 AIP is a systemic disease and is the pancreatic manifestation of IgG4-related systemic disease. Type 2 disease is confined to the pancreas. The intensity of the periductal inflammatory infiltrate and the presence of ductal neutrophilic abscesses are features that assist in distinguishing type 2 AIP from chronic pancreatitis, not otherwise specified. Although imperfect, clinical and imaging features may help distinguish the 2 subtypes of AIP. On the basis of these significant differences between the 2 types of AIP, we advocate the position that all subsequent studies attempt to substratify their patients into these 2 groups.

IgG4-related disease is a newly recognized fibro-inflammatory condition characterized by several features: a tendency to form tumefactive lesions in multiple sites; a characteristic histopathological appearance; and—often but not always—elevated serum IgG4 concentrations. An international symposium on IgG4-related disease was held in Boston, MA, on 4–7 October 2011. The organizing committee comprising 35 IgG4-related disease experts from Japan, Korea, Hong Kong, the United Kingdom, Germany, Italy, Holland, Canada, and the United States, including the clinicians, pathologists, radiologists, and basic scientists. This group represents broad subspecialty expertise in pathology, rheumatology, gastroenterology, allergy, immunology, nephrology, pulmonary medicine, oncology, ophthalmology, and surgery. The histopathology of IgG4-related disease was a specific focus of the international symposium. The primary purpose of this statement is to provide practicing pathologists with a set of guidelines for the diagnosis of IgG4-related disease. The diagnosis of IgG4-related disease rests on the combined presence of the characteristic histopathological appearance and increased numbers of IgG4+ plasma cells. The critical histopathological features are a dense lymphoplasmacytic infiltrate, a storiform pattern of fibrosis, and obliterative phlebitis. We propose a terminology scheme for the diagnosis of IgG4-related disease that is based primarily on the morphological appearance on biopsy. Tissue IgG4 counts and IgG4:IgG ratios are secondary in importance. The guidelines proposed in this statement do not supplant careful clinicopathological correlation and sound clinical judgment. As the spectrum of this disease continues to expand, we advocate the use of strict criteria for accepting newly proposed entities or sites as components of the IgG4-related disease spectrum.