A 40-year-old previously healthy woman presented to the emergency department with 24 hours of dizziness, imbalance, bilateral lower extremity weakness, blurred vision, chest pain, and a painful rash on the left foot with tenderness of the fingers and toes. In the emergency department, the patient’s temperature was 36.7 °C (98.1 °F); blood pressure, 121/82 mm Hg; pulse, 74/min; respiratory rate, 15/min; and oxygen saturation, 99% on room air. Physical examination revealed petechiae within a poorly demarcated erythematous patch on the left dorsal foot (Figure 1, left panel), splinter hemorrhages on the right thumbnail (Figure 1, center panel), and petechial macules on the palms and soles, most numerous on the distal digits. There was no murmur or plop on cardiac auscultation. Neurologic examination findings were significant for left eye nystagmus and inability to adduct the right eye on left gaze, consistent with right-sided internuclear ophthalmoplegia. A computed tomography (CT) scan of the head showed 2 acute infarcts in the right cerebellum. Results of laboratory testing were notable for mild leukocytosis (12.2 × 109/L), mild thrombocytosis (439 × 109/L), and elevated troponin level (4.4 ng/mL); results of a comprehensive metabolic panel and the remainder of the complete blood cell count were normal. An electrocardiogram showed T-wave inversions in lead V2, consistent with a non–ST-segment elevation myocardial infarction. Transthoracic echocardiogram and cardiac CT angiography (Figure 1, right panel) were performed.