Mastocytosis is a rare condition caused by excessive amounts of mast cells gathering in the tissues of the body. These cells release large amounts histamine and other chemicals into the blood, causing symptoms such as a skin rash, itchy skin and hot flushes.
Mast cells are a type of cell found in certain parts of the body, such as the skin and the lining of the lungs and stomach. They play an important role in the immune system (see box, left).
Types of mastocytosis
There are two main types of mastocytosis:
- cutaneous mastocytosis – excessive amounts of mast cells gather in the skin
- systemic mastocytosis – excessive amounts of mast cells gather in body tissues, such as the skin, organs and bones
Cutaneous mastocytosis
Cutaneous mastocytosis usually only affects children. Three-quarters of cases develop in children aged one to four. It is also known as paediatric mastocytosis.
The most common symptom of cutaneous mastocytosis is abnormal growths (lesions) on the skin, such as blisters and spots, which can form a rash on the body.
Systemic mastocytosis
Systemic mastocytosis (also known as mast cell disease) mainly affects adults. People with the condition experience attacks, lasting 15-30 minutes, when their symptoms are particular severe. During an attack they may have:
- allergic reactions, such as itching and flushing
- gut symptoms, such as vomiting and diarrhoea
- bone symptoms, such as thinning of the bones
- changes in mood, headaches and episodes of severe fatigue (tiredness)
These attacks are often triggered by factors such as:
- physical exertion
- certain medications, such as aspirin or antibiotics
- stress or emotional upset
There are three subtypes of systemic mastocytosis, which are described below.
- indolent mastocytosis (accounting for 90% of cases) – where symptoms are mild to moderate and vary from person to person
- aggressive mastocytosis – mast cells invade organs such as the spleen, liver and digestive system, so symptoms are more wide ranging and severe (but skin lesions are rare)
- systematic mastocytosis with associated haematological (blood) disease – the person also develops a condition affecting the blood cells, such as chronic leukaemia, so the outlook depends on the severity of the blood disease
Severe allergic reaction
Because of the excessive amounts of mast cells and their potential to release large amounts of histamine into the blood, people with both cutaneous and systemic mastocytosis have an increased risk of experiencing a severe and life-threatening allergic reaction. The medical term for a severe allergic reaction is anaphylaxis.
If you or your child are diagnosed with mastocytosis, you may be recommended to carry an adrenaline injection kit, which you can use to prevent the symptoms of anaphylaxis from getting worse.
For more information, see the Health A-Z topic on Anaphylaxis.
How common is mastocytosis?
Cutaneous mastocytosis is the most common form of the condition, but it is still very rare in general terms. It is estimated that only 1 in every 1,000 visits to a dermatologist (specialist in treating skin conditions) is due to cutaneous mastocytosis.
Systemic mastocytosis is thought to be much rarer, although exactly how rare is uncertain. One estimate is that 1 in 150,000 people in England have systemic mastocytosis.
The cause of both types of mastocytosis is not fully known.
Outlook
Symptoms of cutaneous mastocytosis usually improve over time, and the disease goes away on its own by the time a child has reached puberty.
The outlook for systemic mastocytosis can vary depending on the type you have. Indolent systemic mastocytosis should not affect life expectancy, but other types can. Some people will go on to develop a serious haematological condition, such as chronic leukaemia.
There is no cure for mastocytosis. Treatment is based on trying to relieve symptoms with medication.
