**1. Spectrum of IgG4-related disease**

IgG4-related disease (IgG4-RD) belongs to quite new disease entities; its name was introduced in the 21st century. In the course of the disease, characteristic infiltrates are formed, composed of mononuclear cells, mainly IgG4 cells. Also, fibrosis of affected organs is observed. In the majority of patients, concomitant increase in serum IgG4 concentration is found, but not in every patient [1, 2].


#### **Table 1.**

*Current nomenclature of most common clinical forms of IgG4-RD.*

In 2011, classification criteria were presented with a spectrum of diseases described so far in medicine that may correspond to IgG4-RD. The first relationship between autoimmune pancreatitis and increased serum IgG4 was observed in 2001 and it is one of the most common manifestations of IgG4-RD-type 1 of autoimmune pancreatitis [3]. Currently, there is a tendency to introduce the name IgG4-RD disease depending on the location of the lesions (**Table 1**) [4].

Due to possible location of pathologic lesions in most of the organs, every physician may have contact with IgG4-RD, independent of his/her speciality.
