Cutaneous vasculitis, hypersensitivity vasculitis, erythema nodosum, and pyoderma gangrenosum.

Cutaneous vasculitis encompasses a highly heterogeneous group of disorders of diverse etiology, pathogenesis, and clinical features. Recent reexamination of clinical pathologic features have yielded no insights assisting our understanding of current clinical classification schemes and strengthening our clinical approach. Erythema nodosum is a common cutaneous disorder for which new etiologies continue to be described. Pyoderma gangrenosum is an uncommon ulcerative cutaneous condition that remains a therapeutic problem.