Systemic mastocytosis is a rare condition in which the body makes many abnormal mast cells. It may also be called systemic mast cell disease (SMCD). Different parts of the body can be affected by SMCD. The most common site is the bone marrow, where blood cells are made. The skin, stomach, bowel, liver, spleen and lymphatic tissue (tissue that our immune system is made from) can also be affected.

Mast cells help to protect us from infection and to heal wounds. They are part of our immune system and are found in the tissues of many parts of our bodies, including the skin, the stomach and bowel. Our immune system sometimes makes us react strongly to irritants such as pollen. This is called an allergy. When we have an allergic reaction our symptoms are caused by the chemicals (histamines) that mast cells release.

Some of the symptoms of SMCD are caused by the mast cells releasing chemicals such as histamines into the bloodstream. These may include :

• headaches
• wheezing
• flushing
• feeling faint or dizzy
• palpitations.

For most people systemic mastocytosis is a mild disease and involves taking treatments to control allergy-type symptoms. But for about 1 in 5 people (20%) the condition can be more serious.

It isn't known what causes SMCD. Some types seem to be linked to other blood disorders but mostly it isn't clear why people develop the condition.

People with a type of SMCD called systemic mastocytosis with AHNMD have a blood disorder as well as abnormal mast cells. There are a number of blood disorders that may be associated with this type of mastocytosis including: myelodysplasia, myeloproliferative disorders, acute myeloid leukaemia and non-Hodgkin lymphoma. Treatment is usually given for the blood disorder as well as for any symptoms caused by the mast cells.

SMCD is usually diagnosed with a bone marrow biopsy. This involves a doctor taking a sample from your hip bone (pelvis). Other tests depend on what symptoms you have. They may involve a combination of tests including: blood tests, endoscopy, X-rays, ultrasound, CT and MRI scans.

In more aggressive types of systemic mastocytosis symptoms may be caused by a build up of abnormal mast cells in one area of the body such as the skin, stomach or bone marrow. Possible symptoms include:

• itchy, red skin rash
• diarrhoea
• feeling sick or being sick
• stomach ulcers
• tummy (abdominal) pain
• bone or muscle pain
• tiredness and breathlessness caused by low levels of red blood cells (anaemia)
• bruising or bleeding caused by low levels of platelets (clotting blood cells).

Symptoms can often be helped by drugs called antihistamines and by steroids. But more aggressive types of SMCD will need other treatments to try to control them.

Because the condition is so rare doctors aren’t sure what the best treatment is. Research is going on to look into this. Chemotherapy drugs may be used or newer types of drugs called tyrosine kinase inhibitors such as imatinib (Glivec) may be tried. Treatment with bone marrow transplants is also being tested in clinical trials.

Reference:

• Qunitas-Cardama A et al (2006). Novel approaches to the therapy of systemic mastocytosis. Cancer, 107,1429-1439.