Clinical case 1. A 42-year-old woman presented to her general practitioner with general weakness and tooth pain. Laboratory assessment showed a WBC count of 80 000/µL, hemoglobin of 6.4 mg/dL, and platelet count of 21 000/µL, which led her physician to make an immediate referral to the local hospital, where a differential blood count revealed 56% myeloid blasts. By that time, the patient was in stable clinical condition with a minimally elevated C-reactive protein of 20 mg/L. She was put on 4 g hydroxyurea (HU) and planned for transferal to our hospital the next morning. During the night, she developed dyspnea requiring oxygen supply. We diagnosed an AML M4eo with inv(16) and started induction treatment with cytarabine plus daunorubicin (7 + 3) at a WBC count of 70 000/µL. Immediate leukapheresis was not possible because of the progressive dyspnea and the increasingly deranged coagulation status. By the next day, the WBC count had gone down to 19 000/µL, but the patient developed respiratory failure requiring mechanical ventilation. The computed tomography (CT) scan result was highly suggestive for leukostasis of the lungs (A), and cranial CT showed multiple focal supratentorial hemorrhages (B). During the next few days, respiratory indices improved, and the patient could be extubated. Early bone marrow response assessment showed a good response with leukemia-free hypoplastic marrow, and after regeneration of peripheral counts, a complete remission (CR) was diagnosed. The patient has currently completed consolidation chemotherapy and is in ongoing CR. The remarkable aspects of this case are (1) the fact that leukostasis developed rapidly even at a WBC count below 100 000/µL, possibly because of the monocytic nature of blasts¹¹ ; (2) cytarabine alone led to a profound and rapid WBC reduction; and (3) the patient recovered from mechanical ventilation because the underlying leukostasis could be treated successfully. (A) Contrast-enhanced CT image (lung window) through the upper fields of the lungs demonstrates parenchymal infiltrates as well as diffuse ground-glass opacities suggestive for leukostasis and myeloblast infiltration. There is sparing of the lung periphery. Note also bilateral pleural effusions. Respiratory failure required mechanical ventilation support as indicated by the endotracheal tube. A central venous catheter in the right brachiocephalic vein and nasogastric tube in the esophagus can be seen. (B) Horizontal plane of native cranial CT scan demonstrating multiple hyperdense lesions in both brain hemispheres indicating hemorrhagic lesions. Accompanying cerebral edema is characterized by loss of gray-white matter differentiation, compression of lateral ventricles, and effacement of sulcal spaces.