**6.8 Retroperitoneal fibrosis and IgG4-RD**

Retroperitoneal fibrosis was reported in 13% of patients with multi-organ involvement in the course of IgG4-RD. Most of the lesions were periaortic or located around iliac vessels. In 33% of patients, hydronephrosis was found, more commonly of one kidney than two [83]. Classifying all cases of IgG4-RD as Ormond's disease is controversial if not confirmed by histopathology, and requires a further well-designed medical analysis. However such a suggestion was made in one publication [84].

## **6.9 Summary of the clinical picture**

IgG4-RD is a disease of multiple systems. It may be located in one or in many organs at the same time. In case of suspected IgG4-RD, all other diseases which may mimic IgG4-RD should be excluded. For rheumatologists it is important to exclude in the differential diagnosis the following: neoplasms including solid lesions and lymphomas, inflammatory and infectious changes, sarcoidosis, vasculitis including granulomatous vasculitis, Sjӧgren syndrome, Castleman's disease, eosinophilic angiocentric fibrosis. As IgG4-RD may involve many organs, imaging diagnostics should always be carried out in order to determine all locations of the disease after diagnosis of the disease.
