Cutaneous manifestations of systemic disease.

The skin should not be thought of as an isolated organ system. When the skin is involved by disease, other organs may be affected as well. Cutaneous xanthomas commonly occur with plasma lipid abnormalities, necrobiosis lipoidica diabeticorum with diabetes mellitus, and the porphyrias with altered heme synthesis. Erythema multiforme and erythema nodosum may be considered hypersensitivity reactions, occurring in response to a wide range of inciting agents, including infections, drugs, neoplasms, and rarely, collagen vascular diseases.