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Rheumatologist should be familiar with the concept of IgG4-related disease (IgG4-RD). Due to the clinical spectrum IgG4-RD can fall directly within the scope of rheumatology and are often diagnosed primarily by rheumatologists. Furthermore, IgG4RD are relevant differential diagnoses for many other rheumatic conditions. Finally, there are an increasing amount of data suggesting an important role of immunological processes observed in IgG4-RD for other rheumatic diseases.

Polyarteritis nodosa (PAN) is a necrotizing vasculitis of medium size arteries that may affect various organs. The clinical appearance is very variable. The most common manifestations are of the skin, the peripheral nervous system presenting as mononeuritis multiplex and the mesenteric and renal blood vessels due to the development of stenoses and small aneurysms. Of the cases one third are estimated to be associated with hepatitis B virus (HBV). The therapy depends on the pathogenesis of the disease: primary PAN is treated with immunosuppressants, whereas patients with HBV-related PAN should receive antiviral therapy and plasmapheresis. Differentiating PAN from other forms of vasculitis can be difficult and requires complex differential diagnostics.

Chronic periaortitis is an inflammatory and fibrosing disease presenting as periaortal fibrosis and formation of aortic aneurysms which are mostly localized in the retroperitoneum and occasionally in the mediastinum. Inflammatory vasculitic involvement of large vessels is also possible. In addition to symptoms of systemic inflammation, mechanical complications also occur whereby obstruction of the ureter is the most frequent. The diagnosis is made by contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) and if the findings are atypical the diagnosis should be confirmed by biopsy. After exclusion of a secondary genesis, in which case therapy of the underlying illness would be necessary, idiopathic chronic periaortitis can be treated with steroids. In cases of refractory and relapsing courses the administration of further immunosuppressive medication can be necessary. Duration of therapy, dosage and indications for immunosuppressive medication are currently unclear and have to be defined in further randomized controlled trials with larger cohorts. If complications occur, interventional or operative treatment can be necessary; in cases of hydronephrosis the placement of double-J-stents is usually sufficient.