Condition	Cause	Characteristics
Cellulitis	Infection	Skin breakdown followed by unilateral painful erythema that is warm to the touch; typically associated with induration, fluctuance, or drainage
Ischemia due to peripheral artery disease	Atherosclerosis or embolism	A cold extremity, absent pulses on Doppler ultrasonography; chronic occlusion leads to collateral blood flow and may be asymptomatic
Necrotizing fasciitis	Severe infection	Rapidly spreading painful erythema, blue-gray skin and bullae, signs of systemic toxicity
Small vessel vasculitis	Inflammatory disease	Affects more than one system, rheumatologic abnormalities on laboratory testing
Vitamin C deficiency (scurvy)	Nutritional deficiency of vitamin C	Areas of hemorrhage in the skin or the mouth; many patients have eschars