Cases from the Osler Medical Service at Johns Hopkins University.

A 73-year-old man who had been receiving chronic anticoagulation treatment with warfarin for multiple prior strokes presented to the hospital because of several weeks of pain in his right calf. He also complained of several months of anorexia and weight loss of 20 lbs. On physical examination, he was thin and showed signs of temporal wasting. There was minimal pitting edema in the right leg, with a positive Homans' sign. Lower extremity Doppler ultrasound showed a popliteal thrombus. The morning after admission, he developed an acutely swollen, painful upper extremity and was found to have an occlusive clot in the left subclavian vein. Because these thrombi occurred in the setting of a therapeutic prothrombin time (international normalized ratio, 2.7) on warfarin, he was begun on treatment with intravenous heparin. What is the diagnosis?