A man in his 60s had 4 months of fatigue, night sweats, weight loss, and tender, nonfluctuant plaques on his scalp and hands, with overlying hemorrhagic crust and necrosis on an erythematous indurated base; clinical evaluation showed pancytopenia, and an acute deep vein thrombosis involving the left common and external iliac veins and distal inferior vena cava. What is the diagnosis and what would you do next?