Diagnosis of Autoimmune Pancreatitis

In 1995 when Yoshida et al. coined the term “autoimmune pancreatitis” they listed several serologic and imaging features that helped them recognize the entity (10). These features formed the basis for the first diagnostic criteria proposed by the Japan Pancreas Society in 2002 (9). In these reports hypergammaglobulinemia and nonspecific markers such as rheumatoid factor and antinuclear antibodies served as serologic markers of AIP. In 2001 Hamano et al. made the observation that elevated serum IgG4 levels were highly sensitive and specific for the diagnosis of autoimmune pancreatitis (AIP) (4). Even though this led to a rapid increase in the number of patients diagnosed with AIP, it soon became clear this was an inadequate biomarker when used in isolation to diagnose AIP. As the larger spectrum of disease became apparent the need for diagnostic criteria to distinguish AIP from other diseases including chronic pancreatitis, pancreatic cancer, and other systemic diseases was evident. Within one decade there were at least six versions of diagnostic criteria published by groups from Japan, Italy, the United States, and Korea (1-3, 5-7). Although the criteria were generally similar, there were major differences including the necessity of ERCP for diagnosis, and the inclusion or exclusion of criteria for other organ involvement and response to steroids. Unfortunately, these differences led to confusion for practicing clinicians and prevented comparison of results between studies. International Consensus Diagnostic Criteria In 2011 a multinational group met to develop diagnostic criteria that would be meaningful for both clinical and research purposes. They achieved a consensus that recognizes our current understanding of AIP, permits flexibility in diagnostic evaluation (e.g., reliance on histology vs. pancreatography), and acknowledges the two AIP subtypes. Importantly, although the typical clinical presentation of patients with AIP is obstructive jaundice, occasionally with a mass, the criteria also permit diagnosis in those with less common disease presentations and indeterminate imaging findings. These criteria are referred to as the International Consensus Diagnostic Criteria (ICDC) for AIP (8). The cardinal clinical features of AIP in the ICDC are based on pancreatic parenchymal imaging, pancreatic ductal imaging (i.e., ERP), serum IgG4 level, other organ involvement, histology of the pancreas, and response to steroid treatment.