Mastocytosis
is the term for a group of disorders caused by too many "mast
cells". It is most common in children, but the more important
forms are seen in both children and adults. Mast cell are found
throughout the body, but are especially plentiful in the skin and
digestive tract. Mast cells are part of the immune defense system.
They are also found around wounds, and seem to play a role in healing
of injuries.
Mast cells work by releasing chemicals that attract white blood
cells to areas of the body where they are needed. 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 having too few mast cells may be incompatible
with life.
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
infiltrate 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.
Urticaria pigmentosa was first described in 1869, while systemic
mastocytosis was first reported in the scientific literature in 1933.
The true incidence of either type of mastocytosis remains unknown, 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
Urticaria pigmentosa can be diagnosed through the abnormally high
concentration of mast cells in the skin. The diagnosis of systemic
mastocytosis can be made by a biopsy showing an increased number of
mast cells in an organ other than the skin. The biochemical hallmark
of the disease is an 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.
Elevations of plasma histamine or mast cell protease are occasionally
seen in patients with allergic diseases, but, unlike mastocytosis
patients, their plasma histamine levels are elevated only temporarily.
Plasma tryptase and histamine levels are persistently increased in
mastocytosis patients.
Other tests that are important in the evaluation of a suspected
case of mastocytosis include a bone marrow examination and a bone
scan. Special stains, such as Giemsa and toluidine blue, are used on a
bone marrow sample to demonstrate the increase in marrow mast cells
that occurs in a large percentage of people with the disease.
Treatment
An array of drugs is used to treat the symptoms of mastocytosis,
including antihistamines (to prevent mast cell release of chemicals),
and anticholinergics (to relieve intestinal cramping). A number of
drugs are used for the treatment of specific symptoms of mastocytosis.
