**6.5 Involvement of the vessels in IgG4-RD**

Lesions of IgG4-RD type usually locate in the aorta in the form of periaortitis, aortic dilatation, and aneurysm. The lesions are usually found in the abdominal aorta [9]. Inflammatory aortic aneurysm is characterized by thickening of the aortic wall, partial fibrosis of adventitia and infiltration composed of inflammatory cells [75]. Similar changes without enlargement of vessel diameter are called periaortitis [9]. The most characteristic location of inflammatory infiltrations for IgG4-RD is the adventitia (external fibrous membrane). In case of thoracic aorta involvement, separation of the aortic layers, lymphoplasmacytic aortitis and isolated aortitis are observed [76, 77]. Arterial wall thickening is relatively low compared to lesions found in the abdominal section. In some patients, aorta involvement may occur as unexpected separation of the aortic layers or sudden cardiac death; other changes in the course of the disease were rarely reported in vessels such as carotid artery, coronary arteries, pulmonary arteries, visceral vessels, mesentery vessels, iliac and vertebral arteries, brain vessels. If present, they were reported as vasculitis or aneurysms [78, 79].

The relationship between IgG4-RD and ANCA-associated vasculitis (AAV) has not been fully explained. It is known that these diseases have a similar clinical picture (asthma symptoms, involvement of nasal sinuses, involvement of lungs and kidneys) and may proceed with increased serum IgG4 concentration and eosinophilia in the peripheral blood. Most publications were dedicated to eosinophilic granulomatosis with vasculitis (EGPA) [9].

### **6.6 Location of IgG4-RD in the nervous system**

Lesions in the central nervous system are rare. If present, they are usually found in the meninges of the brain or cranial nerves. The symptoms concerning cranial nerve involvement are most commonly caused by the presence of pseudotumors and pressure on or infiltration of the nerves [80].
