A 23-year-old woman has had altered consciousness and slurred speech for the past 24 hours. A head CT scan shows a right temporal hemorrhagic infarction. Cerebral angiography shows a distal right middle cerebral arterial occlusion. Within the past 3 years, she has had an episode of pulmonary embolism. A pregnancy 18 months ago ended in miscarriage. Laboratory studies show a false-positive serologic test for syphilis, normal prothrombin time (PT), elevated partial thromboplastin time (PTT), and normal platelet count. Which of the following is the most likely cause of these findings?
Antiphospholipid antibody Disseminated intravascular coagulation Factor V mutation Hypercholesterolemia