Aplastic Anemia

Aplastic anemia is a disorder in which the bone marrow greatly decreases or stops production of blood cells.

Description
The bone marrow (soft tissue which is located within the hard outer shell of the bones) is responsible for the production of all the types of blood cells. The mature forms of these cells include red blood cells, which carry oxygen throughout the body; white blood cells, which fight infection; and platelets, which are involved in clotting.

In aplastic anemia, the basic structure of the marrow becomes abnormal, and those cells responsible for generating blood cells (hematopoietic cells) are greatly decreased in number or absent. These hematopoietic cells are replaced by large quantities of fat.

Yearly, aplastic anemia strikes about 20,000-30,000 people, or 5-10 people in every one million. Although aplastic anemia strikes both males and females of all ages, there are two age groups that have an increased risk. Both young adults (between 15-30 years of age) and the elderly (over the age of 60) have higher rates of aplastic anemia than the general population. While the disorder occurs worldwide, young adults in Asia have a higher disease rate than do populations in North America and Europe.

Causes and symptoms
Aplastic anemia falls into three basic categories, based on the origin of its cause: idiopathic, acquired, and hereditary. In about (50% to) 60% of cases, aplastic anemia is considered to be idiopathic, meaning that the cause of the disorder is unknown.

Acquired Aplastic Anemia
Acquired aplastic anemia refers to those cases where certain environmental factors and physical conditions seem to be associated with development of the disease. Acquired aplastic anemia can be associated with:

• exposure to drugs, especially anti-cancer agents, antibiotics, anti-inflammatory agents, seizure medications, and antithyroid drugs (drugs given to stop the functioning of an overactive thyroid)
• exposure to radiation
• chemical exposure (especially to the organic solvent benzene and certain insecticides)
• infection with certain viruses (especially those causing viral hepatitis, as well as Epstein-Barr virus, parvovirus, and HIV, the virus which can cause AIDS)
• pregnancy
• certain other disorders, including a disease called paroxysmal nocturnal hemoglobinuria, an autoimmune reaction called graft-vs-host disease (which occurs when the body's immune system attacks and destroys the body's own cells), and certain connective tissue diseases

Hereditary Aplastic Anemia
Hereditary aplastic anemia is relatively rare, but does occur in Fanconi's anemia, Shwachman-Diamond syndrome, and dyskeratosis congenita.

Symptoms
Symptoms of aplastic anemia tend to be those of other anemias, including fatigue, weakness, tiny reddish-purple marks (petechiae) on the skin (evidence of pinpoint hemorrhages into the skin), evidence of abnormal bruising, and bleeding from the gums, nose, intestine, or vagina. The patient is likely to appear pale. If the anemia progresses, decreased oxygen circulating in the blood may lead to an increase in heart rate and the sudden appearance of a new heart murmur.

Prognosis
Aplastic anemia is a life-threatening illness. Without treatment, it will almost surely progress to death. Survival depends on how severe the disease is at diagnosis, which type of treatment a patient is eligible for, and what kind of response their body has to that treatment. The worst-prognosis type of aplastic anemia is one associated with very low numbers of a particular type of white blood cell. These patients have a high chance of dying from overwhelming bacterial infections. In fact, 80% of all patients treated with blood transfusions alone die within 18 months to two years. Patients who undergo bone marrow transplantation have a 60-90% chance of being cured of the disease.

BOOKS:
Castro-Malaspina, Hugo, and Richard J. O'Reilly. "Aplastic Anemia and Myelodysplastic Syndromes." In Harrison's Principles of Internal Medicine, ed. Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.

PERIODICALS:
Doney, Kristine, et al. "Primary Treatment of Acquired Aplastic Anemia: Outcomes with Bone Marrow Transplantation and Immunosuppressive Therapy." Annals of Internal Medicine 126 (15 Jan. 1997): 107+.

Young, Neal. "Aplastic Anaemia." The Lancet 346 (22 July 1995): 228+.

Young, Neal, and Jaroslaw Maciejewski. "The Pathophysiology of Acquired Aplastic Anemia." The New England Journal of Medicine 336 (8 May 1997): 1365+.

ORGANIZATIONS:

Aplastic Anemia Foundation of America. P.O. Box 613, Annapolis, MD 21404. (800) 747-2820. http://www.aplastic.org/.

GLOSSARY:
Bone marrow—A substance found in the cavities of bones, especially the long bones and the sternum (breast bone). The bone marrow contains those cells which are responsible for the production of the blood cells (red blood cells, white blood cells, and platelets).

Bone marrow transplant—A procedure in which a quantity of bone marrow is extracted through a needle from a donor, and then passed into a patient to replace the patient's diseased or absent bone marrow.

Hematopoietic cells—Those cells which are lodged within the bone marrow, and which are responsible for producing the cells which circulate in the blood (red blood cells, white blood cells, and platelets).