Question

A 41-year-old woman is brought to the emergency department by her husband due to a 4-day history of profound fatigue, easy bruising, and recurrent nosebleeds. She has no significant past medical history and takes no medications. Vital signs show a temperature of $37.6^\circ \text{C}$ ($99.7^\circ \text{F}$), pulse of $110$/min, respirations of $18$/min, and blood pressure of $105/65$ mm Hg. Physical examination reveals pale mucous membranes, diffuse petechiae over the trunk and extremities, and continuous oozing of blood from a peripheral intravenous catheter site.

Laboratory studies reveal the following:

* Hemoglobin: $7.6$ g/dL
* Leukocyte count: $3,200/\mu\text{L}$
* Platelet count: $18,000/\mu\text{L}$
* Prothrombin time: $22$ seconds
* Activated partial thromboplastin time: $48$ seconds
* Fibrinogen: $80$ mg/dL (Normal: $200$–$400$ mg/dL)
* D-dimer: $8,500$ ng/mL (Normal: $< 500$ ng/mL)

Peripheral blood smear demonstrates large mononuclear cells with bilobed nuclei and abundant azurophilic granules; several of these cells contain multiple, needle-like eosinophilic inclusion bodies.

Which of the following is the most appropriate next step in the management of this patient?