A 26 year-old woman presents to your office and reports feeling usually weak and tired, having trouble concentrating, shortness of breath, especially with activity, pounding sensation in the ears, easy bruising from minor injuries and even brushing her teeth, frequent nosebleeds, heavy menstrual periods, and tiny red spots on her arms. Her past medical history is significant for three urinary tract infections in the last four months. She has no prior exposure to chemicals and reports no drug use. In physical examination, you notice a well-built, well dressed woman with no distress. She has pallor of conjunctiva, the skin and mucous membranes. There are petechiae and ecchymosis on both arms. She has resting tachycardia. You did not notice lymphadenopathy and splenomegaly. Suspecting a blood disorder, you ordered some laboratory tests. The results are as follows. Laboratory results: Neutrophil count: 498//μL; platelet count 19700/μL; hemoglobin 8.2 g/dl; corrected reticulocyte count 0.9% blood smear showed large erythrocytes with increased mean corpuscular volume (MCV). Paucity of platelets and granulocytes. No reticulocytes. Normal lymphocytes. Bone marrow biopsy: readily aspirated, mainly fatty biopsy specimen, markedly hypocellular devoid of marrow progenitors Which of the following is the most likely diagnosis?
