Neutropenia
Neutropenia is an abnormally low number of neutrophils in the blood.
Neutrophils serve as the major defense of the body against acute bacterial and certain fungal infections. Neutrophils usually constitute about 45 to 75% of all white blood cells in the bloodstream. When the neutrophil count falls below 1,000 cells per microliter of blood, the risk of infection increases somewhat; when it falls below 500 cells per microliter, the risk of infection increases greatly. Without the key defense provided by neutrophils, a person has problems controlling infections and is at risk of dying from an infection.
Causes
Neutropenia can develop if neutrophils are used up or destroyed in the bloodstream faster than the bone marrow can make new ones. With some bacterial infections, some allergic disorders, and some drug treatments, neutrophils are destroyed faster than they are produced. People with an autoimmune disease can make antibodies that destroy neutrophils and result in neutropenia. People with an enlarged spleen (see Section 14, Chapter 179) may have a low neutrophil count because the enlarged spleen traps and destroys neutrophils.
Neutropenia can also develop if the production of neutrophils in the bone marrow is reduced, as can occur in some people with cancer, viral infections such as influenza, bacterial infections such as tuberculosis, myelofibrosis, or deficiencies of vitamin B12 or folic acid. People who have received radiation therapy that involves the bone marrow may also develop neutropenia. Many drugs, including phenytoin, chloramphenicol, sulfa drugs, and many drugs used in cancer treatment (chemotherapy), as well as certain toxins (benzene and insecticides) can also impair the bone marrow's ability to produce neutrophils.
Production of neutrophils in the bone marrow is also affected by a severe disorder called aplastic anemia (in which the bone marrow may shut down production of all blood cells (see Section 14, Chapter 172)). Certain rare hereditary diseases also cause the number of neutrophils to decrease.
Symptoms and Diagnosis
Neutropenia can develop suddenly over a few hours or days (acute neutropenia), or it can develop gradually and last for months or years (chronic neutropenia). Because neutropenia itself has no specific symptoms, it is usually diagnosed when an infection occurs. In acute neutropenia, a person can develop fever and painful sores (ulcers) around the mouth and anus. Bacterial pneumonia and other severe infections can follow. In chronic neutropenia, the course may be less severe if the number of neutrophils is not extremely low, and the course can occasionally be intermittent (cyclic neutropenia).
When a person has frequent or unusual infections, a doctor suspects neutropenia and orders a complete blood cell count to make the diagnosis. A low neutrophil count indicates neutropenia. In many cases, the neutropenia is expected and the cause is known, as in those receiving chemotherapy or radiation therapy. When the cause is not known, it must be determined.
A doctor usually takes a sample of bone marrow through a needle (see Section 14, Chapter 170). The bone marrow sample is examined under a microscope to determine whether it looks normal, has a normal number of neutrophil stem cells, and shows normal development of neutrophils. By determining whether the number of stem cells is decreased and whether these cells are maturing normally, the doctor may be able to determine whether the problem lies in faulty production of the cells or whether too many cells are being used or destroyed in the bloodstream. Sometimes, the bone marrow examination indicates that other diseases, such as leukemia or other cancers, or infections, such as tuberculosis, are affecting the bone marrow.
Treatment
The treatment of neutropenia depends on its cause and severity. Drugs that may cause neutropenia are discontinued whenever possible, and exposures to suspected toxins are avoided. Sometimes the bone marrow recovers by itself without treatment. The neutropenia accompanying viral infections (such as influenza) may be transient and resolve after the infection has cleared. People who have mild neutropenia generally have no symptoms and may not need treatment.
People who have severe neutropenia can rapidly succumb to infection because their bodies lack the means to fight invading organisms. When these people develop infections, they are generally hospitalized and immediately given strong antibiotics, even before the cause and exact location of the infection are identified. Fever, the symptom that usually indicates infection in a person who has neutropenia, is an important sign that immediate medical attention is needed.
Growth factors called colony-stimulating factors, which stimulate the production of white blood cells, are sometimes helpful. Corticosteroids may help if the neutropenia is caused by an autoimmune reaction. Antithymocyte globulin or other types of therapy that suppresses the activity of the immune system may be used when a disease such as aplastic anemia is present. Removing an enlarged spleen may cure the neutropenia involved with hypersplenism.
When neutropenia is caused by another disease (such as tuberculosis or leukemia or other cancers), treatment of the underlying disease may resolve the neutropenia. Bone marrow (or stem cell) transplantation is not used to treat neutropenia per se, but it may be recommended to treat certain serious causes of neutropenia, such as aplastic anemia or leukemia.
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