The purple digit: an algorithmic approach to diagnosis.

The acute onset of purple digits is a concerning manifestation and may represent underlying, potentially life-threatening disease. Correctly identifying the etiology of purple digits is essential to proper management, and can aid in the diagnosis of systemic disease. Multiple causes of purple digits and significant overlap in clinical presentation can make diagnosis difficult. Despite the various causes of acute purple digits in the published literature, an algorithmic approach to the evaluation and management of the most common and alarming etiologies has yet to be established. The initial step in evaluating a patient with purple digits is to determine if the cause is associated with hypoxemia or trauma. If the patient is in a stable condition, the dermatologist needs to determine if the process could be related to cold exposure such as Raynaud phenomenon, acrocyanosis, pernio, cryoglobulinemia or frostbite. If the disease occurs independent of temperature, physical examination and histological evaluation of the skin is recommended. The lack of peripheral pulses are concerning for acute arterial thrombosis from peripheral vascular disease or arterial embolism. Non-blanching skin changes on the digit that lack inflammation and microthrombosis most likely represent a bleeding or platelet abnormality; however, if microthrombi are identified a more life-threatening processes such as purpura fulminans or embolic phenomenon may be occurring. Evidence of blood vessel inflammation suggests a leukocytoclastic vasculitis. The patient with a purple blanching digit and normal pulses requires an extensive historical review to help determine the cause. This review presents an algorithmic approach to assist in the evaluation and management of the purple digit.