Systemic mastocytosis

Mastocytosis is a group of rare disorders of both children and adults caused by the presence of too many mast cells (mastocytes) in a person's body. more...

Pathophysiology

Mast cells are located in connective tissue, including the skin, the linings of the stomach and intestine, and other sites. They 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. Because they gather together around wounds, mast cells 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 (angiogenesis). No one with too few or no mast cells has been found, which indicates to some scientists that we may not be able to survive with too few mast cells.

Mast cells express a cell surface receptor termed c-kit (CD117), which is the receptor for scf (stem cell factor). In laboratory studies, scf appears to be important for the proliferation of mast cells, and inhibiting the tyrosine kinase receptor with imatinib (see below) may reduce the symptoms of mastocytosis.

History

Scientists first described urticaria pigmentosa in 1869. Systemic mastocytosis was first reported by scientists in 1936.

Symptoms

Chemicals released by mast cells cause changes in the immune system leading to typical allergy symptoms such as:

• itching
• abdominal cramping
• and even anaphylaxis (shock from allergic or immune causes)

When too many mast cells exist in a person's body, the additional chemicals can cause:

• Skin lesions
• Abdominal discomfort
• Diarrhea
• Stomach ulcers
• Episodes of very low blood pressure (including shock) and faintness
• bone or muscle pain
• Nausea and vomiting

Diagnosis

Doctors can diagnose urticaria pigmentosa (cutaneous mastocytosis, see below) by seeing the characteristic lesions which are dark-brown and fixed. A small skin sample (biopsy) may help confirm the diagnosis.

By taking a biopsy from a different organ, such as the bone marrow, the doctor can diagnose systemic mastocytosis. Using special techniques on a bone marrow sample, the doctor looks for an increase in mast cells. Another sign of this disorder is high levels of certain mast-cell chemicals and proteins in a person's blood and sometimes in the urine.

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