Panniculitis presents with deep erythematous nodules, induration, and tenderness. Clinical lesions of erythema nodosum can appear as deep-seated, erythematous, tender nodules or can resemble bruises, giving rise to the term erythema contusiforme . The lesions tend to be bilateral except in erythema nodosum migrans, which is generally unilateral and slowly expands to form an annular plaque.
Erythema induratum favors the calves, and ulceration is frequent. Oily fluid often drains from the ulcers. Pancreatic panniculitis presents as indurated plaques, most commonly on the lower legs. The subcutaneous fat elsewhere may also be affected, and multiple areas may be affected. Tenderness of the ankles is commonly reported. Another form of panniculitis is subcutaneous fat necrosis of the newborn, which also presents as hard, indurated areas and demonstrates characteristic intracellular crystalline rosettes histologically.
Lipodermatosclerosis represents ischemic fat necrosis associated with venous stasis. Early lesions present as tender nodules of the lower leg. Over time, the skin becomes erythematous and indurated, with constriction of the lower leg giving the appearance of an inverted champagne bottle. Factitial and infectious panniculitis range in appearance from erythematous nodules to draining indurated plaques, whereas lipodystrophies present with loss of subcutaneous fat, giving a gaunt and muscular appearance. This section of the atlas will focus on the range of cutaneous findings that accompany diseases of the fat.