Aplastic Anemia

Aplastic anemia (AA) is a type of bone marrow failures characterized by pancytopenia caused by an insult to the hematopoietic stem cells (HSCs), leading to ineffective hematopoiesis. Therefore, the name “anemia” is a misnomer. AA can be divided into acquired or inherited, e.g., Fanconi anemia or Dyskeratosis Congenita. Given limited space, we only discuss about acquired AA in the chapter. The incidence of acquired AA is very low (<2 per million), However, it tends to be higher in Asia than Western countries. It is considered that patients living in the Asian countries with increased exposure to drugs and toxin and indigenous viruses might be the causes for the higher incidence. Almost half of the cases occur before the age of 40. The ratio of male to female is 1:1. For acquired AA, most commonly, the insult is autoimmune or idiopathic, and if untreated, it is almost universally fatal. Clinically, it is challenging to identify an accurate etiology of the acquired AA and to perform differential diagnosis between AA and other AA mimickers, e.g., hypoplastic myelodysplastic syndrome/neoplasm (MDS), paroxysmal nocturnal hemoglobinuria (PNH), or T/NK-cell large granular lymphocytic leukemia not only because of overlapping bone marrow findings but also the coexistence of these diseases. An accurate diagnosis is critical for appropriate management and the majority of patients require consultation at a tertiary center both for treatment and consideration of allogeneic hematopoietic cell transplantation (allo- HCT).