Gangrene of the Leg during Warfarin Treatment in a Patient with Cancer FREE

Patients with cancer sometimes develop blood clots in the deep veins of the leg, a condition known as deep venous thrombosis. In rare cases, blood clots in the deep veins of the leg become so extensive, involving both large and small blood vessels, that they reduce blood and oxygen supply to tissues. This can cause gangrene (rotting of the tissues). The drug warfarin is typically used to treat deep venous thrombosis. Warfarin thins the blood by interfering with normal blood clotting. It helps the body's normal systems for blood-clot removal to work more effectively. Why some patients with clots in their leg veins develop gangrene while they are taking warfarin has been a mystery.

To find out why and how venous gangrene occurred in a patient with cancer taking warfarin.

A 66-year-old woman in Canada with metastatic lung cancer and a clot in a deep vein of her right leg. Her leg clot was initially treated with two blood thinners, heparin and warfarin. She then developed new clots in her left leg and gangrene of her left foot, even though blood test results showed that warfarin was making her blood very thin.

The researcher studied 11 blood samples obtained from the patient over 8 days during warfarin treatment. The blood samples were tested for clotting and anticlotting substances.

The blood samples showed very high levels of substances called thrombin–antithrombin complexes: This indicates that there was too much blood clotting (hypercoagulability). However, very low levels of an anticlotting substance called protein C were also found. Because warfarin usually reduces levels of thrombin–antithrombin complexes and protein C, in this particular patient the effect of warfarin to reduce protein C so severely without interrupting clotting would lead to worsening of thrombosis and, thus, gangrene.

A single patient was studied. We cannot tell how often warfarin therapy will lead to venous gangrene.

Venous limb gangrene occurs when blood substances that promote blood clotting (procoagulants) are much more active than substances that prevent blood clotting. Warfarin can worsen imbalances by failing to prevent procoagulant states in patients with cancer and simultaneously depleting anticlotting substances such as protein C.