Skin Involvement

Cutaneous lesions may be the clinical expression of inflammatory disorders predominantly affecting skin blood vessels, but may also be part of systemic vasculitis. In particular, skin involvement occurs frequently in the context of the antineutrophil cytoplasmic antibodies (ANCA)-associated vasculitis, which are characterized by inflammatory cell infiltration of the small and medium-sized vessel wall. ANCA-associated vasculitis are rare and systemic diseases, which can be classified based on different distribution of vascular inflammation and the presence or absence of granulomatosis and asthma. Despite their diversities, ANCA-associated vasculitis, namely granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis and microscopic polyangiitis, can all present with a broad variety of cutaneous manifestations, which can appear during the course of these conditions or even as first sign of disease. Among the skin manifestations, palpable purpura represents the most common vasculitis-related lesion, but the cutaneous picture of ANCA-associated vasculitis is typically polymorphic including also papules, nodules, urticarial lesions, livedo, pustules, blisters, and necrotic ulcers. Due to this polymorphism, the diagnosis of skin involvement in ANCA-associated vasculitis is very challenging and must be supported by medical history, physical examination, histology of skin specimens, and ANCA serology. In this chapter, we focus on the cutaneous manifestations that can develop in the context of ANCA-associated vasculitis, describing clinical features, histopathological aspects, and direct immunofluorescence findings for each of these entities. Moreover, we address the differential diagnosis with different dermatological conditions and report the main therapeutic approaches.