PatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.
Synonym: systemic mast cell disease (SMCD)
Mast cells are found in the perivascular spaces of most tissues and contain pro-inflammatory and vasoactive mediators. These mediators are released after IgE receptor cross-linking induced by allergens or other stimuli. Mast cell disorders may involve:
- Either excessive proliferation of mast cells (mastocytosis).
- Normal numbers of cells but abnormal reactivity.
The excess release of mediators can cause clinical features such as pruritus, flushing, nausea, vomiting, diarrhoea, abdominal pain, vascular instability and anaphylaxis. Also, complications may arise when mast cells accumulate in the skin, gastrointestinal tract, bone marrow, liver, spleen, and lymph nodes. The clinical features of systemic mastocytosis are caused by accumulation of clonally derived mast cells in different tissues, including bone marrow, skin, gastrointestinal tract, liver and spleen. Systemic mastocytosis is now classified as a myeloproliferative neoplasm.
Classification of mast cell disorders
The World Health Organization (WHO) classification (simplified here) is:
- Cutaneous mastocytosis - usually children.
- Urticaria pigmentosa (maculopapular cutaneous mastocytosis) - the most common type.
- Diffuse cutaneous mastocytosis (very rare).
- Mastocytoma of skin.
- Systemic mastocytosis:
- Indolent systemic mastocytosis
- Systemic mastocytosis with associated haematological non-mast cell lineage disease (SM-AHNMD).
- Aggressive systemic mastocytosis.
- Mast cell leukaemia (very rare).
- Localised mast cell proliferations (very rare).
- Extracutaneous mastocytoma.
- Extracutaneous mast cell sarcoma.
Telangiectasia macularis eruptiva perstans (TMEP) is a rare form of cutaneous mastocytosis, in which telangiectasia occur together with the rash.
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Mast cell activation syndrome (MCAS)
- MCAS - synonym: mast cell activation disorder (MCAD) - is characterised by the accumulation of genetically altered mast cells and/or abnormal release of mast cell mediators, affecting functions in potentially every organ system, particularly the skin, gastrointestinal tract, and cardiovascular and nervous systems. Investigations are usually normal.
- Patients experience many of the same symptoms as with mastocytosis. Chronic mast cell activation can be difficult to diagnose, especially when symptoms are mild or atypical.
- The use of antihistamines and mast cell membrane-stabilising drugs with symptomatic treatment is often effective.
The cause is unknown but is probably multifactorial. A mutation of the oncogene c-kit D816V is found in many (but not all) cases.
This is a rare and heterogeneous group of disorders, of which urticaria pigmentosa is the most common manifestation. It affects under 1 in 1,000 patients attending dermatology clinics. Estimated incidence is 1 in 150,000.
Possible triggers for mastocytosis symptoms
- Physical stimuli, eg heat, cold, friction, sunlight, fatigue, exercise or fever.
- Emotional stimuli, eg stress.
- Certain foods, eg cheese, spices, shellfish, food preservatives, flavourings and colourings, monosodium glutamate.
- Environmental toxins, eg perfumes, pesticides.
- Insect bites, jelly fish stings, snake bites.
- Infection (bacterial, fungal or viral).
- Drugs, eg alcohol, anaesthetic agents, dextran, aspirin and non-steroidal anti-inflammatory drugs (NSAIDS), antibiotics, opioids, thiamine, quinine, gallamine, procaine, some radiographic dyes, polymyxin B, scopolamine and tubocurarine.
- The rash comprises light brown, itchy, raised patches - on any part of the body.
- The lesions blister when rubbed (Darier's sign) and become red, swollen and itchy. This confirms the presence of mastocytosis.
- Rarely, anaphylactic reactions can occur after mechanical/thermal stimulation of skin lesions.
- Dermatographism may be found on unaffected skin.
- It usually affects infants from a few months of age. The lesions can persist and gradually increase in number for several months or years.
- Symptoms gradually improve as the child gets older, and the condition usually disappears by puberty.
The younger the patient and the smaller the number of the lesions, the higher the probability of spontaneous remission. An adult onset increases the risk of systemic involvement and persistence.
Diffuse cutaneous mastocytosis:
- This usually occurs in the first year of life.
- The rash is very itchy, with generalised yellowish, thickened skin.
- Blisters are large, sometimes haemorrhagic, and occur spontaneously or following mild trauma.
- With more extensive skin involvement, systemic symptoms are more likely. These include flushing, headache, palpitations, abdominal pain, diarrhoea, dyspnoea, wheezing, syncope, hypotensive shock and death.
- Early onset of blisters worsens the prognosis.
Mastocytoma of skin:
- This is a macular, papular or nodular lesion of yellow, brown or reddish colour.
Patients may present with "inexplicable" symptoms related to mast cell mediator release, such as vascular instability, anaphylactic shock, flushing, diarrhoea and headache (sometimes without skin lesions). There is a wide range of symptoms and a variety of triggers (see box). The condition may be unmasked by an anaphylactoid response to a stinging insect. Possible symptoms and signs of systemic mastocytosis are:
- Syncope, hypotension or anaphylactic shock.
- Haematological and bones:
- Peripheral neuropathy.
- Mastocytoma is a benign tumour with uniform growth.
- Mast cell sarcoma is a locally destructive tumour.
- Skin biopsy (with analysis of c-kit D816V).
- Blood tests:
- Urinary histamine levels or 1,4-methylimidazole acetic acid may be elevated.
- If there is suspected systemic involvement (including most adults with suspected mast cell disorders), then complete staging is needed. This includes:
- CXR (or chest CT scan) for lymphadenopathy.
- Gastrointestinal investigations, eg endoscopy and ultrasound of abdomen.
- Bone density scan and skeletal X-rays.
- Bone marrow biopsy/aspirate.
- Other tests include:
- Chromosomal analysis: 20% of patients with systemic mastocytosis have an abnormal karyotype.
- Molecular testing for KIT D816V mutation is always positive but JAK2 V617F is rarely positive.
- The mast cell clone is CD-117 positive and CD-25 and/or CD-2 positive. Expression of CD-25 on mast cells is seen in systemic mastocytosis but not in reactive states of mast cell hyperplasia.
There is a suggested diagnostic protocol. The diagnostic criteria are:
- Major criteria:
- Biopsy finding of multiple dense accumulations of mast cells in bone marrow or in other non-skin tissue.
- Minor criteria:
- In bone marrow biopsy, more than 25% of the mast cells are spindle-shaped; or in bone marrow smears, more than 25% of the mast cells are atypical mast cells.
- Detection of a point mutation at codon 816 in the kit receptor gene. This may be found in bone marrow or blood or other internal organs.
- Mast cells in bone marrow, blood, or other internal organs are found to have on their surface the kit receptor plus CD2 and/or CD25.
- Serum total tryptase level persistently greater than 20 ng/mL. This criterion cannot be used if the patient has a clonal non-mast cell associated haematological disorder.
- The diagnosis of systemic mastocytosis may be made if one major and one minor criterion are present, or if three minor criteria are fulfilled.
- Other pruritic rashes, eg other forms of urticaria.
- Other causes of flushing:
- Other causes of abdominal pain, peptic ulceration or liver disease, including:
- Other haematological or myeloproliferative disorders.
This is concerned mainly with symptom control, as there is currently no cure. Systemic mastocytosis is usually managed by haematologists.
- Those prone to acute severe symptoms should avoid trigger factors where possible, wear a medical emergency identification bracelet or similar and carry written treatment protocols from their specialist.
- Acute anaphylaxis is treated with intramuscular adrenaline (epinephrine), antihistamines (H1 and H2 receptor blockers), fluids and pressor agents.
- Patients with recurrent anaphylactoid reactions should carry injectable adrenaline (epinephrine) in pen format for emergency use.
- Consider immunotherapy against insect venom.
Skin and vascular symptoms
- For pruritus, weals and flushing - H1 and H2 receptor antagonists such as chlorphenamine, ketotifen and cimetidine.
- Mast cell stabilizers: sodium cromoglicate, nedocromil and ketotifen.
- Local corticosteroids for skin lesions. Intralesional steroid injection is sometimes used.
- Psoralen in combination with ultraviolet A (PUVA) treatment - gives temporary benefit for skin lesions.
- H2 receptor antagonists or proton pump inhibitors for peptic ulceration.
- Oral sodium cromoglicate for diarrhoea and abdominal pain.
- Anticholinergics for diarrhoea.
Other possible systemic treatments
- Leukotriene inhibitors have been used in the treatment of systemic mastocytosis.
- Systemic corticosteroids may be helpful for malabsorption, ascites, and bone pain, to prevent anaphylaxis and for severe skin disease.
- Low-dose aspirin may be helpful for symptoms resistant to H1 and H2 antagonists alone, but must be started cautiously under supervision:
- The patient, premedicated with H1 and H2 antihistamines, may take small doses of aspirin, titrated slowly to reach a plasma level of 20-30 mg/100 mL.
- Treatment should be started in a controlled environment, because aspirin can induce mast cell mediator release and subsequent cardiovascular collapse.
- Oral sodium cromoglicate may help.
- Osteoporosis prevention/treatment - calcium, vitamin D, and bisphosphonates.
Drugs to avoid
- Beta-blockers are contra-indicated in patients with systemic mastocytosis undergoing surgery - these drugs may counteract endogenous adrenaline (epinephrine) and may precipitate anaphylaxis.
- Avoid alpha-blockers and cholinergic antagonists.
- Splenectomy may be helpful for patients with significant hypersplenism or portal hypertension (it may reduce the mast cell burden and improve cytopenias).
- Aggressive systemic forms of mastocytosis may be treated with interferon alfa, with or without corticosteroids, or cladribine. In some cases, more intensive treatments such as imatinib, or drug combinations, may be considered.
- Bone marrow transplantation may be considered in some extreme cases but is currently experimental treatment.
- For patients with mast cell sarcoma, surgical excision with consecutive radiation and/or high-dose chemotherapy.
A protocol for management in children is available.
- Childhood cases of urticaria pigmentosa and mastocytoma often resolve spontaneously. Adults are more likely to develop the systemic form of the disease.
- This has no known cure and tends to be progressive.
- Prognosis depends on the degree of haematological and organ involvement, as the classification (above) suggests.
- Indolent systemic mastocytosis has a relatively good prognosis - decades of life, using mainly symptomatic treatment, although life-threatening problems can occur.
- In systemic mastocytosis with associated haematological non-mast cell lineage disease (SM-AHNMD), the prognosis depends on the course of the associated haematological disorder.
- Agressive systemic mastocytosis and mast cell leukaemia have a poorer prognosis. The median survival for aggressive systemic mastocytosis is 41 months and for mast cell leukaemia it is 2 months.
- Mastocytoma is a benign tumour with a good prognosis.
- Mast cell sarcoma is locally destructive and usually has poor prognosis.
Further reading & references
- Valent P, Horny HP, Escribano L, et al; Diagnostic criteria and classification of mastocytosis: a consensus proposal. Leuk Res. 2001 Jul;25(7):603-25.
- Villar SS, Perez-Somarriba J, Costa TS, et al; A 38 year old woman with hypotensive shock at the onset of menstruation: case outcome. BMJ. 2009 Mar 9;338:b247. doi: 10.1136/bmj.b247.
- Horny HP, Sotlar K, Valent P; Mastocytosis: state of the art. Pathobiology. 2007;74(2):121-32.
- Metcalfe DD; Mast cells and mastocytosis. Blood. 2008 Aug 15;112(4):946-56.
- Krishnan K et al; Mastocytosis, Systemic, Medscape, Jul 2010
- Urticaria pigmentosa, DermNet NZ, December 2008; includes pictures
- Akin C, Valent P, Metcalfe DD; Mast cell activation syndrome: Proposed diagnostic criteria. J Allergy Clin Immunol. 2010 Dec;126(6):1099-104.e4. Epub 2010 Oct 28.
- Valent P, Horny HP, Triggiani M, et al; Clinical and Laboratory Parameters of Mast Cell Activation as Basis for the Int Arch Allergy Immunol. 2011 May 16;156(2):119-127.
- Molderings GJ, Brettner S, Homann J, et al; Mast cell activation disease: a concise practical guide for diagnostic workup and J Hematol Oncol. 2011 Mar 22;4:10.
- Silva I, Carvalho S, Pinto PL, et al; Mastocytosis: a rare case of anaphylaxis in paediatric age and literature review. Allergol Immunopathol (Madr). 2008 May-Jun;36(3):154-63.
- Hogan D et al; Mastocytosis, Medscape, Jun 2010; overview, predominantly of skin manifestations - useful images
- Lee JK, Whittaker SJ, Enns RA, et al; Gastrointestinal manifestations of systemic mastocytosis. World J Gastroenterol. 2008 Dec 7;14(45):7005-8.
- Koenig M, Morel J, Reynaud J, et al; An unusual cause of spontaneous bleeding in the intensive care unit - mastocytosis: a case report. Cases J. 2008 Aug 18;1(1):100.
- Dubois AE; Mastocytosis and Hymenoptera allergy. Curr Opin Allergy Clin Immunol. 2004 Aug;4(4):291-5.
- Tamhankar PM, Suvarna J, Deshmukh CT; Cutaneous Mastocytosis. Getting beneath the skin of the issue: a case report. Cases J. 2009 Jan 20;2(1):69.
- Izikson L, English JC 3rd, Zirwas MJ; The flushing patient: differential diagnosis, workup, and treatment. J Am Acad Dermatol. 2006 Aug;55(2):193-208.
- Heide R, Beishuizen A, De Groot H, et al; Mastocytosis in children: a protocol for management. Pediatr Dermatol. 2008 Jul-Aug;25(4):493-500.
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Dr Sean Kavanagh, Dr Naomi Hartree
Dr Colin Tidy
Dr Hayley Willacy