Blue (or purple) toe syndrome.

UNLABELLED The blue (or purple) toe syndrome consists of the development of blue or violaceous discoloration of one or more toes in the absence of obvious trauma, serious cold-induced injury, or disorders producing generalized cyanosis. The major general categories are: (1) decreased arterial flow, (2) impaired venous outflow, and (3) abnormal circulating blood. Depending on its pathogenesis, the discoloration may be blanching or nonblanching. An accurate diagnosis is critical, because many of the causes threaten life and limb, but the patient's medical history, accompanying nondermatologic findings on physical examination, and a discriminating use of laboratory tests are usually more important than the nature of the cutaneous abnormalities in determining the cause. LEARNING OBJECTIVES After completing this learning activity, participants should be able to define the blue (or purple) toe syndrome, categorize the causes, and recognize the important historical, clinical, and laboratory findings that differentiate the causes and lead to the correct diagnosis.