The exact cause of mastocytosis is unknown, but genetic mutations are known to be involved.

A genetic mutation occurs when normal instructions carried in certain genes become “scrambled”. This results in some of the body’s processes not working normally.

The kit mutation

Most people with cutaneous or systemic mastocytosis have a genetic mutation known as the kit mutation. It makes their mast cells more sensitive to the effects of a type of protein called stem cell factor (SCF).

SCF plays an important role in stimulating the production and survival 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 that 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. This leads to symptoms of mastocytosis.

In a few cases of mastocytosis, it appears that the kit mutation is inherited (passed down through families). However, in most cases, the mutation is spontaneous (it occurs for no apparent reason).

There are several tests available to confirm a diagnosis of mastocytosis, depending on which type you have.

Cutaneous mastocytosis

A physical examination of the skin is the first stage in diagnosing cutaneous mastocytosis – a form of the condition that’s much more common in children than adults.

Your child’s GP or dermatologist (skin specialist) may rub affected areas of skin to see if they become red, inflamed and itchy (known as Darier’s sign).

A biopsy can usually be carried out to confirm a diagnosis. This involves removing a small sample of affected skin so that it can be checked under a microscope to see whether it contains an abnormally high number of mast cells.

Systemic mastocytosis

Five tests are commonly used to look for systemic mastocytosis. They are described below.

Full blood count (FBC)

A small sample of blood is taken and different types of blood cells in the sample are measured. Unusually low numbers of blood cells could be caused by excessive numbers of mast cells in your bone marrow.

Blood tryptase levels

The levels of an enzyme in your blood called tryptase are measured using a blood test. Tryptase is produced by mast cells and other cells.

Having more than 20 nanograms of tryptase in a millilitre of blood may suggest you have excessive numbers of mast cells in your bone marrow or other organs (it can also be raised by other conditions). A nanogram is a billionth of a gram.

Ultrasound scan

An ultrasound scan can be used to check whether your liver and spleen are swollen, which can occur in some cases of systemic mastocytosis.

An ultrasound scanner uses high-frequency sound waves to create an image of part of the inside of the body.

DEXA scan

A dual energy X-ray (DEXA) scan is a type of X-ray that measures the amount of calcium in bones.

Low levels of calcium are usually a sign that your bones have become weak and brittle (osteoporosis), which could be due to excessive numbers of mast cells accumulating inside your bones. Mast cells release substances that cause the bones to thin.

Bone marrow test

If the above tests suggest that you may have systemic mastocytosis, it’s likely you’ll be referred for a bone marrow test. You’ll be given a local anaesthetic and a long needle will be inserted through your skin and into the bone underneath, usually in the pelvis.

The needle will be used to remove a small sample of bone marrow, which can be examined to see whether it contains an abnormally high number of mast cells.

The bone marrow can also be tested for the “kit mutation”, which is known to be associated with most cases of systemic mastocytosis (see the causes of mastocytosis).

Mastocytosis is a rare condition caused by an excess number of mast cells gathering in the body’s tissues.

Mast cells

Mast cells are produced in the bone marrow (the spongy tissue found in the hollow centres of some bones).

Mast cells live longer than normal cells. They’re an important part of the immune system and help fight infection.

They are found in parts of the body that are vulnerable to infection, such as the skin, stomach and lining of the lungs.

When mast cells detect an allergen (a substance that triggers an allergic reaction), they release histamine and other chemicals into the bloodstream. Histamine makes the blood vessels expand and the surrounding skin itchy and swollen.

Mast cells sometimes mistake harmless substances, such as pollen, for infectious germs, and trigger the process of swelling (inflammation).

This can cause the skin to become red, swollen and itchy, and it can also create a build-up of mucus in the airways, which become narrower. This is known as an allergic reaction.

Read more about the symptoms of mastocytosis.

Types of mastocytosis

There are two main types of mastocytosis – cutaneous mastocytosis and systemic mastocytosis.

Cutaneous mastocytosis

In cutaneous mastocytosis, mast cells gather in the skin but aren’t found in large numbers elsewhere in the body.

Cutaneous mastocytosis mainly affects children, with three-quarters of cases occurring in children who are between one and four years of age. It’s also known as paediatric mastocytosis.

The most common symptom of cutaneous mastocytosis is abnormal growths (lesions) on the skin, such as bumps and spots, which can form on the body and can sometimes blister.

Systemic mastocytosis

In systemic mastocytosis, mast cells gather in body tissues, such as the skin, organs and bones. The condition mainly affects adults.

Some people with systemic mastocytosis may experience episodes of severe symptoms that last 15-30 minutes. Many people don’t have any problems.

During an episode you may have:

• skin reactions – such as itching and flushing
• gut symptoms – such as vomiting and diarrhoea
• muscle and joint pain
• mood changes, headaches and episodes of fatigue (tiredness)

The episodes are often triggered by:

• physical exertion
• certain medications – such as aspirin or antibiotics
• stress or emotional upset
• allergic reactions to foods or stings

There are three subtypes of systemic mastocytosis. They are:

• indolent mastocytosis – symptoms are usually mild to moderate and vary from person to person; indolent mastocytosis accounts for around 90% of adult systemic mastocytosis cases
• aggressive mastocytosis – where mast cells multiply in organs, such as the spleen, liver and digestive system; the symptoms are more wide-ranging and severe, although skin lesions are less common
• systematic mastocytosis with associated blood (haematological) disease – where a condition that affects the blood cells, such as chronic leukaemia, also develops

Severe allergic reaction

People with mastocytosis have an increased risk of having a severe and life-threatening allergic reaction. This is known as anaphylaxis.

The increased risk of anaphylaxis is due to the abnormally high number of mast cells and their potential to release large amounts of histamine into the blood.

If you or your child has mastocytosis, you may need to carry an adrenaline injection pen, which can be used to treat the symptoms of anaphylaxis. 

What causes mastocytosis?

The cause or causes of mastocytosis aren’t fully known, but there’s thought to be an association with a genetic mutation known as the “kit mutation”.

Genetic mutations occur when the normal instructions carried in certain genes become “scrambled”. This results in some of the body’s processes not working normally.

Read more about the causes of mastocytosis.

Diagnosing mastocytosis

A physical examination of the skin is the first stage in diagnosing cutaneous mastocytosis.

Your child’s GP or dermatologist (skin specialist) may rub the affected areas of skin to see if they become red, inflamed and itchy (known as Darier’s sign).

It’s usually possible to confirm a diagnosis by carrying out a biopsy (where a small skin sample is taken and checked for mast cells).

Five tests are commonly used to look for systemic mastocytosis. They are:

• a full blood count (FBC)
• measuring blood tryptase levels
• an ultrasound scan to look for enlargement of the liver and spleen
• a DEXA scan to measure bone density 
• a bone marrow biopsy test

A diagnosis of systemic mastocytosis is usually made by finding typical changes on a bone marrow biopsy.

Read more about diagnosing mastocytosis.

Treating mastocytosis

There’s no cure for mastocytosis, so the aim of treatment is to try to relieve the symptoms.

Treatment options will depend on the type of mastocytosis and severity of symptoms.

Mild to moderate cases of cutaneous mastocytosis can be treated with steroid cream (topical corticosteroids). Steroid cream reduces the number of mast cells that can release histamine and trigger swelling (inflammation) in the skin.

Antihistamines can also be used to treat the symptoms of cutaneous or indolent mastocytosis, such as red skin and itchiness. Antihistamines are a type of medication that block the effects of histamine. They’re often used to treat allergic conditions.

Read more about treating mastocytosis.

Outlook

In children, the symptoms of cutaneous mastocytosis usually improve over time, but remain stable in adults. In most cases, the condition gets better 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 shouldn’t affect life expectancy, but other types can. Some people develop a serious haematological condition, such as chronic leukaemia.

Mastocytosis causes a wide range of symptoms, which can vary depending on the type of mastocytosis you have.

Cutaneous mastocytosis

Skin lesions are a characteristic of cutaneous mastocytosis. A skin lesion is any type of abnormality that affects the skin. Types of lesions known to occur in cutaneous mastocytosis include:

• small areas of skin that change colour (macules)
• small firm raised bumps (papules)
• larger raised red bumps (nodules)
• large raised areas of skin noticeable to the touch (plaques)
• blisters – which mainly affect young children with mastocytomas (tumours consisting of mast cells) or diffuse cutaneous mastocytosis (a rare form of cutaneous mastocytosis)

Lesions usually develop on the trunk (the body, excluding head, neck and limbs). The lesions, known as urticaria pigmentosa, are usually yellow-tan to reddish-brown in colour, and can range from 1mm to several centimetres in size.

The number of lesions that develop on the skin can vary widely. For example, it’s possible for only one lesion to develop, or more than 1,000.

Stroking the affected areas of skin can make it swollen, itchy and red.

Systemic mastocytosis

If you have systemic mastocytosis, you may develop sudden episodes of symptoms that last for around 15-30 minutes. The most common symptoms experienced during an episode are:

• hot flushing – described as a dry feeling of heat, rather than the sort of wet heat you experience when sweating
• heart palpitations (forceful or rapid heartbeat)
• dizziness (lightheadedness)

Less common symptoms during an episode include:

• headache
• shortness of breath
• chest pain
• nausea
• diarrhoea 

Once the episode has passed, you’ll probably feel lethargic (sluggish) for several hours.

The episodes are caused by the mast cells suddenly releasing excessive amounts of histamine, usually after you’re exposed to certain triggers. Triggers known to cause episodes include:

• physical factors – such as heat, overheating, cold, fatigue and physical exertion
• emotional factors – such as stress and excitement
• insect bites or stings – such as flea bites or a wasp sting
• infection – such as the cold or flu
• alcohol 
• certain medications, such as ibuprofen, aspirin and antibiotics
• certain foods – such as cheese, shellfish and spices

Abnormal mast cells in your bone marrow and organs can also cause related symptoms, including:

• stomach pain caused by peptic ulcers
• loss of appetite
• joint pain
• weakness
• fatigue
• changes in mental state – such as confusion, irritability, poor attention span and impaired memory
• urinary symptoms – such as needing to pass urine frequently or pain when urinating

In more severe cases of mastocytosis, the following symptoms may occur:

• weight loss
• swelling of the lymph nodes
• swelling of the liver – which can cause jaundice and make you feel lethargic
• swelling of the spleen – which can cause tummy (abdominal) and shoulder pain

Low blood pressure (hypotension)

Some people with severe symptoms will experience a sudden fall in blood pressure during an attack. Low blood pressure (hypotension) can trigger a number of associated symptoms, such as:

• dizziness
• fainting (a sudden, temporary loss of consciousness)
• blurred vision
• confusion
• general weakness

Anaphylaxis

If you have systemic mastocytosis or extensive cutaneous mastocytosis, your risk of anaphylaxis (a severe allergic reaction) is increased.

It’s therefore important to look out for the initial symptoms of anaphylaxis, which include:

• itchy skin or a raised, red skin rash
• swollen eyes, lips, hands and feet
• feeling lightheaded or faint
• narrowing of the airways, which can cause wheezing and breathing difficulties
• abdominal pain, nausea and vomiting

Dial 999 immediately and ask for an ambulance if you think you or someone else is experiencing symptoms of anaphylaxis.

The treatment options for mastocytosis depend on which type you have and how severe your symptoms are.

Steroid cream

Mild to moderate cases of cutaneous mastocytosis can be treated with a very strong steroid cream (topical corticosteroids) for a limited length of time (usually up to six weeks).

Steroid cream reduces the number of mast cells that can release histamine and trigger inflammation inside the skin.

Side effects of steroid cream when used too much include:

• thinning of the skin, which can sometimes result in permanent stretch marks
• a temporary reduction in the pigmentation of the skin
• the affected area of skin bruising easily

To reduce the risk of side effects, you should only apply the cream to areas of skin affected by lesions.

Antihistamines

Antihistamines can also be used to treat symptoms of cutaneous or indolent mastocytosis, such as itchiness and skin redness.

Antihistamines are a type of medication that block the effects of histamine. They’re widely used to treat allergic conditions.

Side effects of some “classical” antihistamines include:

• headache 
• dry mouth 
• dry nose

However, these side effects should pass quickly once you’re used to the medication. Modern second generation antihistamines don’t usually cause these side effects.

Sodium cromoglicate

Sodium cromoglicate is a medication used to treat conjunctivitis, asthma and food allergy. It may also be used to treat gut symptoms of mastocytosis but isn’t absorbed well from the bowel.

Sodium cromoglicate is a mast cell stabiliser, which means it reduces the amount of chemicals released by the mast cells. This helps relieve symptoms such as diarrhoea.

A case report published in 2010 describes a patient with mastocytosis whose symptoms improved after taking antihistamines and sodium cromoglicate capsules. Their bone pain, fatigue and headache improved further after also taking inhaled sodium cromoglicate.

Nausea and joint pain have been reported in some people taking sodium cromoglicate. A topical form (applied to the skin) of sodium cromoglicate is available that may help with itching. However, it’s not routinely available on prescription.

PUVA

More severe symptoms of cutaneous mastocytosis, such as severe itchy skin, may require a type of treatment called 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 reduce lesions in the skin.

You can only have a limited number of PUVA sessions because using the treatment too many times (thought to be around 150 sessions) may increase your risk of developing skin cancer.

Steroid tablets

If symptoms such as itchiness are particularly severe, corticosteroid tablets (oral corticosteroids) may be prescribed on a short-term basis. However, this is rare.

A short course of corticosteroid tablets may be recommended if you have bone pain due to mastocytosis or anaphylaxis (a severe allergic reaction).

Side effects of oral corticosteroids 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 cell activity in your bones, you’ll be given a type of medication called bisphosphonates.

Bisphosphonates slow the process of bone breakdown, while allowing production of new bone to continue as normal, which improves your bone density.

You may also be given calcium supplements, as calcium helps to strengthen bones.

Read more about treating osteoporosis.

H2-receptor antagonists

If you have stomach pain caused by a stomach ulcer (peptic ulcer), you’ll 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 stomach lining). 

Read more about treating a peptic ulcer.

Interferon alpha

Originally designed to treat cancer, interferon alpha has proved effective in treating some cases of aggressive mastocytosis. It’s not known exactly why this is, but it appears the medication reduces the production of mast cells inside the bone marrow.

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

Imatinib

Imatinib is an alternative medication to interferon alpha. It’s taken as a tablet and blocks the effects of an enzyme called tyrosine kinase, which helps stimulate production of mast cells.

However, imatinib should only be used for people who don’t have the kit mutation, and it doesn’t work for most cases of mastocytosis.

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 38C (100.4F)
• headache
• aching muscles
• diarrhoea
• tiredness

Nilotinib and dasatinib

Nilotinib or dasatinib may be recommended if you don’t respond to treatment with imatinib. They work in much the same way, blocking the effects of tyrosine kinase.

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 it’s also been shown to be useful in treating aggressive systematic mastocytosis. However, cladribine hasn’t been approved (licensed) to treat mastocytosis.

Read more about the licensing of medication.

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

Like imatinib, nilotinib and dasatinib, cladribine will also make you more vulnerable to the effects of infection, so you should report possible symptoms of infection (see above) 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 about treating the most common haematological conditions see:

• treating acute myeloid leukaemia 
• treating chronic myeloid leukaemia
• treating acute lymphoblastic leukaemia
• treating chronic lymphocytic leukaemia
• treating lymphoma 
• treating multiple myeloma

Myeloproliferative neoplasms are also haematological disorders that can be associated with mastocytosis.

Using an adrenaline injection pen

Due to your increased risk of anaphylaxis, you may be given an adrenaline injection pen to use in an emergency.

Adrenaline is a natural chemical that helps fight the effects of histamine, while also relieving breathing difficulties. Each pen contains a single dose of adrenaline (0.3mg for adults or 0.15mg for children). There are three types:

• EpiPen
• Jext
• Emerade

These auto-injectors release adrenaline when jabbed or pressed against the outer thigh. The injections can be given through clothing.

If you’re given an adrenaline injection pen you need to keep an eye on its expiry date because it won’t be effective beyond this date.