How is morphology of vasculitis?

Classified by the vessel size affected (small, medium, mixed or large) • Clinical morphology correlates with the size of the affected blood vessels : -Small vessel: palpable purpura (urticarial lesions in rare cases, e.g., urticarial vasculitis) -Small to medium vessel: subcutaneous nodules, purpura and FIXED livedo reticularis (also called livedo racemosa). Ulceration and necrosis may be present in medium-vessel vasculitis. -Large vessel: claudication, ulceration and necrosis • Diseases may involve more than one size of vessel • Systemic vasculitis may involve vessels in other organs