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Mastocytosis
Overview
Mastocytosis is a disorder in both children and adults that is caused by the presence of too many mast cells in a person's body. Located in skin, the linings of the stomach and intestine, and connective tissue (such as cartilage or tendons), mast cells may play an important role in helping defend these tissues from disease. By releasing chemical "alarms" such as histamine, mast cells attract other key players of the immune defense system to areas of the body where they are needed.
Mast cells seem to have other roles as well. Found to congregate around wounds, they may play a part in wound healing. For example, the typical itching you feel around a healing scab may be caused by histamine released by mast cells. Researchers also think mast cells may have a role in the growth of blood vessels. No one with too few or no mast cells has ever been found, which indicates to some scientists that we may not be able to survive with too few mast cells.
The presence of too many mast cells, or mastocytosis, can occur in two forms -- cutaneous and systemic. The most common cutaneous (skin) form is also called urticaria pigmentosa, which occurs when mast cells get into the skin. Systemic mastocytosis is caused by the accumulation of mast cells in the tissues and can affect organs such as the liver, spleen, bone marrow, and small intestine.
Scientists first described urticaria pigmentosa in 1869, while systemic mastocytosis was first reported in the scientific literature in 1933. No one is sure about how many people have either type of mastocytosis, but mastocytosis generally is considered to be an "orphan disease." (Orphan diseases affect approximately 200,000 or fewer people in the United States.)
Symptoms
Chemicals released by mast cells cause physiological changes that lead to typical allergic responses such as hives, itching, abdominal cramping, and even shock. When too many mast cells exist in a person's body, the additional chemicals can cause bone pain, abdominal discomfort, nausea and vomiting, ulcers, diarrhea, skin lesions, and episodes of hypotension (very low blood pressure and faintness) or anaphylaxis (shock).
Diagnosis
Doctors can diagnose urticaria pigmentosa by looking for abnormally high concentrations of mast cells in a patient's skin. By taking a biopsy (cutting out a tiny piece) of an organ other than the skin, the doctor can diagnose systemic mastocytosis if there are an increased number of mast cells. The biochemical hallmark of the disease is a significant elevation of histamine or mast cell tryptase protein in blood. Urine may also contain high levels of histamine metabolites (products) as well as metabolites of prostaglandin D2. Doctors occasionally see elevations of plasma histamine or mast cell protease in patients with allergic diseases, but, unlike mastocytosis patients, their plasma histamine levels are elevated only temporarily.
Other tests that help the doctor evaluate a suspected case of mastocytosis include a bone marrow examination and a bone scan. Special techniques are used on a bone marrow sample to show the increase in collections of mast cells that occur in a large number of people with this disorder.
Treatment
The doctor uses several medicines to treat the symptoms of mastocytosis, including antihistamines (to prevent mast cell release of chemicals) and anticholinergics (to relieve intestinal cramping). A number of medicines are used to treat the specific signs and symptoms of mastocytosis.
- Itching and skin complaints are frequently treated with drugs called Hl antihistamines.
- Ulcer-like symptoms are relieved by another class of antihistamines called H2 anti-ulcer antihistamines and by proton pump inhibitors.
- Severe flushing (redness, usually in the face) and hypotension (low blood pressure) are treated with H1 and H2 antihistamines before symptoms appear, and with epinephrine after symptoms begin.
- Skin lesions (sores) can be temporarily reduced by topical steroids. If there are only a few lesions, a doctor may remove them surgically.
- Malabsorption (when the body can't take in nutrients) can be treated with steroids.
In rare cases in which mastocytosis is malignant, cancerous, or associated with a blood disorder, steroids and/or chemotherapy may be necessary.
Research
National Institute of Allergy and Infectious Diseases (NIAID) scientists have been studying and treating patients with mastocytosis for several years at the National Institutes of Health (NIH) Clinical Center.
Some of the most important research advances for this rare disorder include improved diagnosis
of mast cell disease, identification of growth factors that are responsible for increased mast cell production, and improved treatment. For example, researchers have developed drugs that help block the action of chemicals released from mast cells. Researchers are currently evaluating drugs, which may stop mast cells from being produced.
Scientists are also focusing on identifying disease-associated mutations (changes). Two such mutations have been identified at NIH in a receptor for a mast cell growth factor. Understanding such mutations may help researchers to understand the causes of mastocytosis, improve diagnosis, and develop better treatments.
NIAID, a
component of the National Institutes of
Health, supports research on AIDS,
tuberculosis and other infectious diseases as
well as allergies and immunology.
Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious
Diseases
National Institutes of Health
Bethesda, MD 20892
Public Health
Service
U.S. Department of Health and Human Services
June 2000
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