"Essential" cutaneous vasculitis: what every rheumatologist should know about vasculitis of the skin.

Although the classification of small-and medium-vessel vasculitides involving the skin remains complex and imperfect, a substantial body of knowledge related to cutaneous vasculitis exists. Some components of this knowledge, though beyond the usual purview of rheumatologists, are essential to understanding the vasculitides. The correct interpretation of cutaneous findings combined with a properly performed skin biopsy yields important insights not only into underlying diagnoses, but also into the pathophysiological mechanisms of individual cases. In this review, we discuss a classification scheme for the cutaneous vasculitides, outline the work-up for evaluating patients with these disorders, and describe the essential features of the major categories of skin vasculitis.