APLASTIC ANEMIA

APLASTIC ANEMIA

APLASTIC ANEMIA

Aplastic anemia is a condition of bone marrow failure that arises from suppression of, or injury to, the hemato­poietic stem cell. The bone marrow becomes hypoplastic, fails to produce mature blood cells, and pancytopenia develops.

Causes

Stem cells in the bone marrow produce blood cells — red cells, white cells and platelets. In aplastic anemia, stem cells are damaged. As a result, the bone marrow is either empty (aplastic) or contains few blood cells (hypoplastic).

The most common cause of aplastic anemia is from your immune system attacking the stem cells in your bone marrow. Other factors that can injure bone marrow and affect blood cell production include:

  • Radiation and chemotherapy treatments. While these cancer-fighting therapies kill cancer cells, they can also damage healthy cells, including stem cells in bone marrow. Aplastic anemia can be a temporary side effect of these treatments.
  • Exposure to toxic chemicals. Toxic chemicals, such as some used in pesticides and insecticides, and benzene, an ingredient in gasoline, have been linked to aplastic anemia. This type of anemia might improve if you avoid repeated exposure to the chemicals that caused your illness.
  • Use of certain drugs. Some medications, such as those used to treat rheumatoid arthritis and some antibiotics, can cause aplastic anemia.
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  • Autoimmune disorders. An autoimmune disorder, in which your immune system attacks healthy cells, might involve stem cells in your bone marrow.
  • A viral infection. Viral infections that affect bone marrow can play a role in the development of aplastic anemia. Viruses that have been linked to aplastic anemia include hepatitis, Epstein-Barr, cytomegalovirus, parvovirus B19 and HIV.
  • Pregnancy. Your immune system might attack your bone marrow during pregnancy.
  • Unknown factors. In many cases, doctors aren’t able to identify the cause of aplastic anemia (idiopathic aplastic anemia).

Symptoms

Aplastic anemia can have no symptoms. When present, signs and symptoms can include:

  • Fatigue
  • Shortness of breath
  • Rapid or irregular heart rate
  • Pale skin
  • Frequent or prolonged infections
  • Unexplained or easy bruising
  • Nosebleeds and bleeding gums
  • Prolonged bleeding from cuts
  • Skin rash
  • Dizziness
  • Headache
  • Fever

Aplastic anemia can be short-lived, or it can become chronic. It can be severe and even fatal.

Diagnosis

The following tests can help diagnose aplastic anemia:

  • Blood tests. Normally, red blood cell, white blood cell and platelet levels stay within certain ranges. In aplastic anemia all three of these blood cell levels are low.
  • Bone marrow biopsy. A doctor uses a needle to remove a small sample of bone marrow from a large bone in your body, such as your hipbone. The sample is examined under a microscope to rule out other blood-related diseases. In aplastic anemia, bone marrow contains fewer blood cells than normal. Confirming a diagnosis of aplastic anemia requires a bone marrow biopsy.

DIFFERENTIAL DIAGNOSIS

Aplastic anemia must be differentiated from other causes of pancytopenia. Hypocellular forms of myelo­dysplasia or acute leukemia may occasionally be confused with aplastic anemia. These are differentiated by the presence of cellular morphologic abnormalities, increased percentage of blasts, or abnormal karyotype in bone marrow cells typical of MDS or acute leukemia.

Hairy cell leukemia has been misdiagnosed as aplastic anemia and should be recog­nized by the presence of splenomegaly and by abnormal “hairy” lymphoid cells in a hypocellular bone marrow biopsy.

Pancytopenia with a normocellular bone marrow may be due to systemic lupus erythematosus, disseminated infection, hypersplenism, nutritional (eg, vitamin B12 or folate) defi­ciency, or myelodysplasia. Isolated thrombocytopenia may occur early as aplastic anemia develops and may be confused with immune thrombocytopenia.

Treatment

Mild cases of aplastic anemia may be treated with support­ive care, including erythropoietic (epoetin or darbepoetin) or myeloid (filgrastim or sargramostim) growth factors, or both. Red blood cell transfusions and platelet transfusions are given as necessary, and antibiotics are used to treat infections.

Severe aplastic anemia is defined by a neutrophil count of less than 500/mcL, platelets less than 20,000/mcL, retic­ulocytes less than 1%, and bone marrow cellularity less than 20%. The treatment of choice for young adults (under age 40 years) who have an HLA-matched sibling is alloge­neic bone marrow transplantation. Children or young adults may also benefit from allogeneic bone marrow transplantation using an unrelated donor. Because of the increased risks associated with unrelated donor allogeneic bone marrow transplantation compared to sibling donors, this treatment is usually reserved for patients who have not responded to immunosuppressive therapy.

For adults over age 40 years or those without HLA-matched hematopoietic stem cell donors, the treatment of choice for severe aplastic anemia is immunosuppression with equine antithymocyte globulin (ATG) plus cyclospo­rine.

Equine ATG is given in the hospital in conjunction with transfusion and antibiotic support. A proven regimen is equine ATG 40 mg/kg/day intravenously for 4 days in combination with cyclosporine, 6 mg/kg orally twice daily. Equine ATG is superior to rabbit ATG, resulting in a higher response rate and better survival. ATG should be used in combination with corticosteroids (prednisone or methylprednisolone 1–2 mg/kg/

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day orally for 1 week, followed by a taper over 2 weeks) to avoid ATG infusion reactions and serum sickness. Responses usually occur in 1–3 months and are usually only partial, but the blood counts rise high enough to give patients a safe and transfu­sion-free life. The full benefit of immunosuppression is generally assessed at 4 months post-equine ATG.

Cyclo­sporine is maintained at full dose for 6 months and then stopped in responding patients. Androgens (such as fluoxymesterone 10–20 mg/day orally in divided doses) have been widely used in the past, with a low response rate, and may be considered in mild cases. The thrombopoietin mimetic, eltrombopag, may help increase platelets (and also red blood cells and white blood cells) in patients with refractory aplastic anemia.

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