Cryoglobulinemia of the fingers
Cryoglobulinemia is caused by an abnormal protein that is occasionally found in the blood of people with multiple myeloma, leukemia, and certain forms of pneumonia. It causes blood to gel at low temperatures. In this picture, cryoglobulinemia has reduced blood flow in the fingers so much the fingers have turned dark. The black areas are gangrene resulting from lack of blood flow.