Cyanosis or necrosis of the fingers is an ischemic symptom of the upper extremity in the clinical manifestations of subclavian artery steal syndrome: intermittent dyskinesia, upper extremity weakness, pain and sensory abnormalities are common in that order, and rarely cause cyanosis or necrosis of the fingers. Factors causing theft of blood from the subclavian artery are occlusion in the subclavian artery or the proximal side of the cephalic trunk, but theft does not always occur. There are many physiological or anatomical factors that produce retrograde vertebral artery blood flow, the most important of which is the degree of subclavian artery stenosis, which is often greater in patients with blood theft than in those without blood theft in terms of systolic pressure difference between the two upper extremities. In addition, the condition of the collateral circulation is also looked at. The following is the differential diagnosis of cyanosis or necrosis of the fingers: 1, purplish palm If the palm color is black and red, purplish palm, we should consider serious heart disease, such as coronary heart disease, asthma, etc. When the inflammation is not controlled to sepsis, the palm color will also return to the microcirculatory stasis caused by purplish red. This is a danger signal to improve early. 2, hand skin purplish Skin purplish is the type of skin purplish.