Erythema nodosum (EN) is usually painful and tender. It is a reactive, inflammatory panniculitis that appears as indurated, erythematous nodules that can be single or multiple. The lesions are 1 to 20 cm in diameter and are hot to the touch. Older lesions often have a bluish, brownish, yellow–green, or purplish tinge and resemble contusions (Fig. 52-1). Borders are not sharply demarcated. Extensor surfaces of the lower leg, thigh, and ankle are the favored sites, although arms and other areas are occasionally affected. When multiple, EN nodules are usually bilateral, but not necessarily symmetric. Fever, arthralgia, and malaise may accompany or precede the eruption. The disease is much more common in women than men.