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.

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

Anaphylaxis

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 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 the UK have systemic mastocytosis.

The cause of both types of mastocytosis is not fully known.

Outlook

The outlook for most cases of cutaneous mastocytosis is very good. Symptoms 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 subtype. It is moderately good for indolent systemic mastocytosis, which should not affect life expectancy.

The outlook for the other subtypes of systemic mastocytosis is less favourable, especially if a person develops a serious haematological condition, such as chronic leukaemia.

There is no cure for any type of mastocytosis. Treatment is based on trying to relieve symptoms with medication.

The cause (or causes) of mastocytosis are uncertain, although genetic mutations are known to be involved. A genetic mutation occurs when the normal instructions that are carried in certain genes become ‘scrambled’. This means that some of the body’s processes will not work in the normal way.

The c-KIT mutation

There is evidence that most people with either cutaneous or systemic mastocytosis have a genetic mutation known as the c-KIT mutation. This makes their bodies more sensitive to the effects of a type of protein called stem cell factor (SCF).

SCF plays an important role in stimulating the production of certain cells, such as blood cells and mast cells, inside the bone marrow. Bone marrow is the soft, jelly-like tissue found in the hollow centre of all large bones. It contains stem cells, which are capable of producing specialist cells, such as mast cells.

When the bone marrow is exposed to SCF, it produces more mast cells than the body can cope with, which leads to the symptoms of mastocytosis.

In a number of cases of mastocytosis, it appears that the c-KIT mutation was inherited (passed down through families). However, in most cases the mutation was spontaneous, i.e. it happened for no apparent reason.

Steroid cream

Mild to moderate cases of cutaneous mastocytosis can be treated with steroid cream (topical corticosteroids). Steroid cream prevents the mast cells releasing histamine and triggering the process of inflammation inside the skin.

Side effects of steroid cream include:

• thinning of the skin, which can sometimes result in permanent stretch marks
• red or purple discolouration of the skin
• the appearance of red spots or lines on the skin, which are caused by expanded blood vessels
• the affected area of skin bruising easily
• the affected area of skin becoming more vulnerable to infection (topical corticosteroids should not be used on infected skin)

To reduce the risk of side effects, you should only apply the cream to areas of the skin affected by lesions. For more information, see the A-Z topic on topical corticosteroids.

Antihistamines

Antihistamines may also be used to treat symptoms of cutaneous or indolent mastocytosis, such as itchiness and redness of the skin. Antihistamines are a type of medication that block the effects of histamine. They are widely used in the treatment of allergic conditions.

Side effects of antihistamines include:

• headache
• dry mouth
• dry nose

These side effects should pass quickly. For more information, see the Health A-Z topic on antihistamines.

Sodium cromoglicate

Sodium cromoglicate (Nalcrom) is a medication used to treat allergic conditions of the eye, rhinitis and food allergy. It is also used as an unlicensed medication for the treatment of mastocytosis. See the box to the left for information about unlicensed treatments.

It is a mast cell stabiliser, which means that it reduces the amount of chemicals released by the mast cells. This helps to relieve symptoms such as diarrhoea, itching and flushing of the skin.

Nausea, skin rashes and joint pains have been reported in some people taking sodium cromoglicate.

PUVA

The more severe symptoms of cutaneous mastocytosis, such as severe itchy skin, may require a type of treatment known as psoralen plus ultraviolet A (PUVA). PUVA involves taking a medication called psoralen, which makes the skin more sensitive to the effects of ultraviolet light.

The skin is then exposed to a wavelength of light called ultraviolet A (UVA), which helps to remove lesions from the skin.

The patient can only receive a limited number of PUVA sessions as using the treatment too many times (thought to be around 200-250 sessions) increases their risk of developing skin cancer.

Steroid tablets

During times when symptoms such as itchiness are particularly severe, tablets containing corticosteroids (oral corticosteroids) may be prescribed on a short-term basis.

For example, a short course of corticosteroid tablets may be recommended if you have bone pain or you have a previous history of anaphylaxis (severe allergic reaction).

Side effects of oral corticosteroids that are used on a short-term basis include:

• an increase in appetite
• weight gain
• insomnia
• fluid retention
• mood changes, such as feeling irritable or anxious 

Bisphosphonates and calcium supplements

If you have osteoporosis (weakened bones) due to abnormal mast activity in your bones, you will be given a type of medication called bisphosphonates. Bisphosphonates slow the process of bone breakdown while allowing the production of new bone to continue as normal, which improves your bone density.

You may also be given calcium supplements (calcium helps strengthen the bones). For more information, see the A-Z page on Treating osteoporosis.

H2-receptor antagonists

If you have symptoms of stomach pain due to peptic ulcers, you will be given a medication called a H2-receptor antagonist. This blocks the effects of histamine in the stomach (histamine stimulates the production of stomach acid, which damages the lining of the stomach). For more information, see the A-Z page on Treating a peptic ulcer.

Interferon alpha

Originally designed to treat cancer, interferon alpha has proved effective in treating some cases of aggressive mastocytosis. Exactly why this is the case is uncertain, although it appears that the medication reduces the production of mast cells inside the bone marrow.

Interferon alpha is given by injection. Most people will have flu-like symptoms such as chills, a high temperature and joint pain when they first start taking interferon alpha. However, these symptoms should improve over time as your body gets used to the medicine.

Imatinib

An alternative medication to interferon alpha is imatinib tablets. Imatinib blocks the effects of an enzyme called tyrosine kinase, which helps stimulate the production of mast cells.

However, imatinib should only be used for people who do not have the c-KIT mutation, and it does not work for all cases of mastocytosis.

Side effects include:

• nausea
• diarrhoea
• headaches
• leg aches and cramps
• fluid retention
• eye pain and watering of the eyes
• itchy rash

These side effects are usually mild to moderate, and should improve after a few months as your body gets used to the medication.

Imatinib can also make you more vulnerable to infection. Contact your GP immediately if you develop possible signs of an infection, such as:

• high temperature (fever) of or above 38ºC (101.4ºF)
• headache
• aching muscles
• diarrhoea
• tiredness

Nilotinib and dasatinib

Nilotinib or dasatinib may be tried when people do not respond to treatment with imatinib. They work in much the same way, blocking the effects of tyrosine kinase.

Side effects include:

• nausea
• constipation
• diarrhoea
• headache
• tiredness
• itching
• rash

The medication will make you more vulnerable to infection, so report possible symptoms of infection to your GP immediately.

Cladribine

Cladribine was originally designed to treat leukaemia (cancer of the white blood cells), but has since proved effective in treating aggressive systematic mastocytosis.

Cladribine suppresses the activity of your immune system. It is given by infusion, which means it is slowly released into your body via a drip in your arm over the course of two hours.

Side effects of cladribine include:

• skin rash
• fatigue (tiredness)
• breathlessness
• nausea
• vomiting

Again, cladribine will make you more vulnerable to the effects of infection, so you should report possible symptoms of infection to your GP immediately.

Treatments for haematological (blood) disease

Systemic mastocytosis with associated haematological disease will be treated in the same way as aggressive systematic mastocytosis (with either interferon alpha, imatinib, nilotinib or cladribine) with a number of additional treatments for the related haematological condition.

For more information on treating the most common haematological conditions, see:

• acute leukaemia – treatment
• chronic leukaemia – treatment
• lymphoma – treatment
• multiple myeloma – treatment