Bone marrow failure due to hematopoietic stem cell deficiency (CD34⁺).

Causes:- Autoimmune- Radiation and drugs (eg, benzene, chloramphenicol, alkylating agents, antimetabolites)- Viral agents (parvovirus B19, EBV, HIV, hepatitis viruses)- Fanconi anemia (DNA repair defect causing bone marrow failure); also short stature, ↑ incidence of tumors/leukemia, café-au-lait spots, thumb/radial defects- Idiopathic (immune mediated, 1° stem cell defect); may follow acute hepatitis

Findings:- ↓ reticulocyte count, ↑ EPO- Pancytopenia characterized by severe anemia, leukopenia, and thrombocytopenia- Normal cell morphology, but hypocellular bone marrow with fatty infiltration (dry bone marrow tap).

Symptoms: fatigue, malaise, pallor, purpura, mucosal bleeding, petechiae, infection.

Treatment: withdrawal of offending agent, immunosuppressive regimens (eg, antithymocyte globulin, cyclosporine), bone marrow allograft, RBC/platelet transfusion, bone marrow stimulation (eg, GM-CSF).