Clinical classification of vasculitis

Clinical classification of vasculitis is needed to facilitate diagnosis and management of the disease as well as to assign patients to defined groups for clinical studies. Caliber and size of the vessels predominantly involved strongly influence the clinical features of the different forms of vasculitis and therefore are one major criterion for classification. As such, panarteritis nodosa involves medium-sized vessels and presents on the skin with subcutaneous nodules and livedo racemosa, while it does not cause glomerulonephritis. Leukocytoclastic vasculitis (LcV) involves the small vessels, resulting in palpable purpura, and sometimes also in glomerulonephritis. The classification systems of the American College of Rheumatology (ACR) and of the Chapel Hill Consensus Conference (CHCC) have gained wide acceptance. Yet, they need to be updated, especially with regard to LcV, the most common vasculitis of the skin. Here distinctions must be made for prognostic, diagnostic and therapeutic reasons between IgG/IgM- and IgA-associated LcV (Henoch-Schoenlein purpura, HSP), as well as between HSP of children and HSP of adult age. The latter bears the highest, while IgG/IgM-associated LcV bears the lowest risk for complications. This update on the clinical classification of vaculitis is based on the ACR and CHCC system and focuses on those forms which regularly cause cutaneous symptoms. It provides a survey on the vasculitic syndromes and should help in deciding when i) extensive diagnostic procedures are needed in patients with LcV, ii) therapy should be less or more aggressive, e.g. in cutaneous versus systemic PAN, iii) therapy should be promptly initiated, e.g. when any form of severe, ANCA-associated vasculitis is suspected.