Hypersensitivity vasculitis

Cutaneous small-vessel vasculitis (CSVV), also known as hypersensitivity vasculitis, cutaneous leukocytoclastic vasculitis, hypersensitivity angiitis, cutaneous leukocytoclastic angiitis, cutaneous necrotizing vasculitis and cutaneous necrotizing venulitis, is inflammation of small blood vessels (usually post-capillary venules in the dermis), characterized by palpable purpura.:831 It is the most common vasculitis seen in clinical practice. Cutaneous small-vessel vasculitis (CSVV), also known as hypersensitivity vasculitis, cutaneous leukocytoclastic vasculitis, hypersensitivity angiitis, cutaneous leukocytoclastic angiitis, cutaneous necrotizing vasculitis and cutaneous necrotizing venulitis, is inflammation of small blood vessels (usually post-capillary venules in the dermis), characterized by palpable purpura.:831 It is the most common vasculitis seen in clinical practice. 'Leukocytoclastic' refers to the damage caused by nuclear debris from infiltrating neutrophils in and around the vessels. Initially red to pink, flat spots (formally, 'macules') and raised bumps (formally, 'papules') may be seen on the skin. Once fully developed, the classic appearance is 'non-blanching, palpable purpura'. This appears as deep red to purple spots that feel raised to the touch. Purpura refers to the red-purple discolored spots, while palpable implies that these spots can be felt as raised from the surrounding skin. Additionally, when gently pressed, the color does not fade to a lighter color ('non-blanching'). The red-purple color of the lesions is due to the inflammation in the blood vessels causing red blood cells to escape into the dermis skin layer. Small fluid-filled blisters (or 'vesicles'), pus-filled bumps resembling a pimple (or 'pustules'), or shallow ulcers may also develop but are less common. The location of skin lesions varies but are most commonly found symmetrically below the waist, primarily on the buttocks and legs. Other distributions include localized areas on the upper body or over several areas of the body. With treatment, the lesions typically resolve in weeks to months and leave behind flat spots that are darker than the surrounding skin. (see 'Postinflammatory hyperpigmentation' on 'Hyperpigmentation') A portion of cases may be persistent or recurrent. This tends to occur when the vasculitis is associated with chronic conditions such as connective tissue diseases. In most cases skin lesions do not cause symptoms, however itching, burning, or pain may occur.