Systemic mastocytosis: symptoms, diagnosis, subtypes and treatment

Mast cells are made in the bone marrow and are an important part of the immune system. The NHS explains that when they detect an allergen they release histamine and other chemicals into the bloodstream, which makes blood vessels expand and the skin itchy and swollen and can narrow the airways. In mastocytosis there are too many of these cells.

There are two main types: cutaneous mastocytosis, which mainly affects children and is confined to the skin, and systemic mastocytosis, which mainly affects adults and in which mast cells gather in body tissues such as the skin, internal organs and bones. There are several subtypes of systemic mastocytosis depending on the symptoms.

The NHS describes three main subtypes of systemic mastocytosis.

Some people with systemic mastocytosis experience episodes of symptoms, but many do not have any problems. The NHS symptoms page says the most common symptoms during an episode are hot flushes, a forceful or rapid heartbeat and feeling light-headed, with headache, chest pain, feeling sick and diarrhoea less common. Episodes are caused by mast cells suddenly releasing excessive histamine, usually after exposure to triggers.

Triggers listed by the NHS include heat, overheating, cold, fatigue and physical exertion; stress and excitement; insect bites or stings; infection such as a cold or flu; alcohol; certain medicines such as ibuprofen, aspirin and antibiotics; and certain foods such as cheese, shellfish and spices. Abnormal mast cells in bone marrow and organs can also cause stomach pain from peptic ulcers, joint pain, weakness, fatigue and changes in mental state such as confusion, irritability and impaired memory. In more severe cases there may be weight loss, swollen lymph nodes, liver or spleen swelling and low blood pressure with dizziness or fainting.

The NHS says people with systemic mastocytosis or extensive cutaneous mastocytosis have an increased risk of anaphylaxis. Initial symptoms include itchy skin or a raised red rash, swollen eyes, lips, hands and feet, feeling lightheaded or faint, narrowing of the airways causing wheezing and breathing difficulties, stomach pain and feeling or being sick. It advises dialling 999 immediately and asking for an ambulance if you think you or someone else is experiencing anaphylaxis.

You may need to carry an adrenaline auto-injector, according to the NHS. Ask your specialist team for a written emergency plan and make sure family and colleagues know what to do.

The NHS lists the tests commonly used to look for systemic mastocytosis: blood tests including a full blood count and measurement of blood tryptase levels; an ultrasound scan to look for enlargement of the liver and spleen if it seems likely; a DEXA scan to measure bone density; and a bone marrow biopsy, in which a local anaesthetic is used and a long needle is inserted into the bone, usually in the pelvis. A diagnosis is usually made by finding typical changes on the bone marrow biopsy.

The cause is not fully known; the NHS says there is thought to be an association with a change in a gene known as the KIT mutation, which in most cases happens for no apparent reason and only very rarely appears to be passed down in families.

The NHS says there is no cure for mastocytosis, so the aim is to relieve symptoms, depending on the type and severity. It also notes that nearly all medicines used are unlicensed for mastocytosis, and that experts may use them when benefits outweigh risks. Options include the following.

• Antihistamines for itchiness and redness in cutaneous or indolent disease.

• Sodium cromoglicate, a mast cell stabiliser, for gut symptoms such as diarrhoea and stomach pain.

• Steroid cream, PUVA light treatment or short courses of steroid tablets for severe skin symptoms, bone pain or anaphylaxis.

• Bisphosphonates and calcium supplements for weakened bones, and H2-receptor antagonists for stomach ulcers.

• Interferon alpha or imatinib for some aggressive cases, and nilotinib or dasatinib if imatinib does not work.

• Midostaurin, which the NHS describes as a licensed medicine for advanced systemic mastocytosis.

NICE guidance says midostaurin (Rydapt) is available on the NHS as a possible treatment for advanced systemic mastocytosis in adults, covering aggressive systemic mastocytosis, systemic mastocytosis with an associated haematological neoplasm and mast cell leukaemia, and that avapritinib (Ayvakyt) is also available on the NHS for the same group. Your healthcare professionals should discuss how well each works, the side effects and how treatment affects daily life.

The NHS says indolent systemic mastocytosis should not affect life expectancy but other types can, and a few people develop a serious blood condition such as chronic leukaemia over their lifetime. NICE lists the UK Mastocytosis Support Group among organisations that can give advice and support. On the NHS, care is typically led by haematology with input from dermatology, allergy, gastroenterology and bone specialists; private specialist opinions are possible, but advanced-disease drugs are delivered through specialist NHS units. The NHS mastocytosis page used here shows a scheduled review date that has passed, so ask your team for current advice.