Introduction

Acquired aplastic anemia (AA) is a rare but potentially fatal bone marrow failure syndrome characterized by pancytopenia. It can be acquired secondary to exposure to radiation, drugs, chemicals, and infections, or as part of an autoimmune disorder. However, most commonly it is idiopathic in origin. Inherited disorders such as Fanconi anemia, dyskeratosis congenital, and Shwachman's syndrome as well as acquired disorders such as paroxysmal nocturnal hemoglobinuria can lead to AA, and are not discussed in this chapter.

AA can present with varying severity. The International AA Study Group has established criteria for the diagnosis of severe aplastic anemia (SAA).37 For the diagnosis of SAA, the bone marrow cellularity should be less than 25% of expected and two out of the following three criteria should be present (1) ANC <0.5 X 109/lt; (2) platelets <20 X 109/lt; and (3) reticulocytes <1%. Very severe aplastic anemia (VSAA) is defined as for SAA but with an ANC <0.2 X 109/lt. Patients not fulfilling criteria for SAA or VSAA have nonsevere AA.

Allogeneic stem cell transplant is a curative option in patients with this diagnosis. It is reserved for the treatment of patients with SAA or VSAA. It can also be considered for patients with nonsevere AA who have failed immunosuppressive therapy. An approach to the treatment of patients with a diagnosis of AA is outlined in Chapter 45.

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