**3. Epidemiology and clinical characteristics**

AIP is increasingly recognized. For example, 900 cases were known in Japan in 2002 [19]; 2790 in 2007 [20]; and 5745 in 2011 [21]. The calculated prevalence was 4.6/100,000, while the incidence 1.4/100,000/yr. Experiences from different regions of the world have been increasingly published; the annual number of papers increased exponentially from 39 in 2000 to 935 in 2017, as found in PubMed Central. We also observed a marked increase in the diagnosis of AIP in Chile [18]. However, the worldwide increase in the frequency of this disease is probably mainly due to its better recognition rather than a-so-important increase in incidence. The more frequent type 1 AIP is part of a systemic IgG4- related disease. A male dominance has been observed; about two thirds of patients are men. The average age is above 50 years. However, there are also women in considerable number. The pancreatic affection is frequently associated with manifestation of the same disease in other organs. Recurrence in the pancreas or in other organs is relatively frequent in this form. Type 2 AIP has been described later, but it is also recognized with a growing frequency. No gender difference was described, and the disease affects young people; the mean age is no more than 30 years. The only associated disease is inflammatory bowel disease (IBD), mainly ulcerative colitis, which can occur simultaneously with the pancreatitis or any other period, before or after the AIP. This form of pancreatitis seldom recurs (**Table 1**)


#### **Table 1.**

*Clinical characteristics of two types of autoimmune pancreatitis.*
