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Author: Dr Anthony Yung, Dermatologist, Hamilton, New Zealand; Copy Editor: Clare Morrison; Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, March 2014.
Mastocytosis is the term for a diverse group of conditions where a single (or clonal) population of mast cells accumulate in one or more tissues, for example, skin, bone marrow, liver, spleen, gastrointestinal tract and lymph nodes.
The severity of symptoms depends on the number of mast cells in the tissues. A high load of mast cells leads to more severe symptoms. Cutaneous mastocytosis causes itching, swelling and blistering of the affected skin, particularly when it is rubbed or scratched.
Most forms of mastocytosis are caused by a mutation of the KIT gene on the 4q12 chromosome – a mutation that increases cellular reproduction. The c-KIT gene mutation creates an overgrowth of one cell line of mast cells. This clonal expansion of mast cells leads to areas of abnormal skin that easily reddens, swells and itches. The c-KIT mutation can also lead to the proliferation of mast cells within the bone marrow, resulting in systemic mastocytosis.
In some cases, the genetic disorder is inherited, but in most cases, it is spontaneous, and there is no family history of mastocytosis.
Mast cells are healthy cells in the body, usually found in the skin and other tissues. Mast cells have a role in the early steps of the body’s coordination of healing responses to an injury. Granules within the mast cells contain histamine and other chemicals.
When a mast cell is activated, these chemicals are released into the surrounding skin. Mast cell chemicals are mediators of inflammation, and cause the blood vessels to leak, resulting in localised itching, swelling, redness and sometimes blistering. This reaction is normal in insect bites and is thought to be a protective mechanism. For example, a mosquito injects saliva when it bites. The saliva triggers mast cell activation to a varying degree, depending on the individual's hypersensitivity to the saliva. The unpleasant itch soon persuades the person to try to avoid getting bitten again.
Rubbing an area of skin affected by mastocytosis may also activate the mast cells. The rubbed skin becomes reddened, swollen and itchy within a few minutes (Darier sign). In young children, the rubbed area may later blister.
Cutaneous mastocytosis is usually diagnosed by its clinical appearance and positive Darier sign. However, a skin biopsy may be helpful for confirmation (see maculopapular cutaneous mastocytosis pathology).
Mast cells may be difficult to see on standard histology with haematoxylin and eosin staining (H&E). They can be identified with special stains, such as Giemsa, toluidine blue, Astra blue or immuno-histochemical stains like tryptase and CD117 (this stains for c-KIT membrane receptor on the surface of mast cells).
A blood test showing high levels of tryptase suggests systemic involvement.
Mastocytosis can be broadly characterised into two groups:
The World Health Organisation (WHO) classifies mastocytosis (2016) as:
A positive Darier sign characterises all forms of cutaneous mastocytosis.
Approximately two-thirds of cases of cutaneous mastocytosis occur in children.
Cutaneous mastocytosis is classified as follows:
Solitary mastocytoma and maculopapular mastocytoma are the most common forms of mastocytosis in children.
A solitary mastocytoma present in infancy as an itchy area of a reddish or yellowish-brown thickened patch of skin. Mastocytomas generally entirely or mostly resolve in time.
Maculopapular cutaneous mastocytosis was previously called urticaria pigmentosa. It is the most common form of mastocytosis in adults and children.
Maculopapular mastocytosis in adults is unlikely to resolve with time. It is associated with systemic involvement, where the mastocytosis spreads to more than one tissue (see below).
Diffuse cutaneous mastocytosis presenting in infancy usually presents as diffuse redness of the skin (erythroderma), sometimes with widespread blistering of the skin. Adults and adolescents with diffuse cutaneous mastocytosis often have a generalised thickening leathery appearance and texture to most or all of their skin, with a positive Darier sign.
Telangiectatic cutaneous mastocytosis is also known as telangiectasia macularis eruptiva perstans (TMEP). Telangiectatic cutaneous mastocytosis is very persistent and may sometimes lead to systemic involvement. The name relates to extensive telangiectases.
Systemic mastocytosis is diagnosed by the presence of a certain number of features: 1 major criterion and 1 or more minor criteria or the presence of 3 minor criteria. Diagnosis requires tissue biopsy and the use of special stains.
Systemic mastocytosis occurs more commonly in adults than children (it is extremely rare in children).
Indolent systemic mastocytosis is the most common and least serious presentation of systemic mastocytosis in adults – it is characterised by a low mast cell burden (<30%), the presence of mediator-related symptoms such as flushing and diarrhoea, and skin involvement (usually maculopapular cutaneous mastocytosis, see above).
SM-AHNMD accounts for one-third of all systemic mastocytosis cases. It is associated with concurrent myeloproliferative neoplasms (in which there is increased bone marrow production of blood cells) and myelodysplasia (in which the bone marrow produces too few blood cells).
Aggressive systemic mastocytosis is due to uncontrolled neoplastic cell proliferation and leads to impaired organ function. It results in flushing, itching, low blood pressure, anaphylaxis, diarrhoea and bleeding from the gastrointestinal tract. These patients may have high serum tryptase levels.
Complications may include:
Mast cell leukaemia is a rare disease of circulating malignant mast cells with a very poor prognosis.
Mast cell sarcoma is a solid tumour of malignant mast cells.
Extracutaneous mastocytoma is a benign mast cell tumour where a localised area of mast cell proliferation is not in the skin.
Patients with solitary mastocytoma generally require no work up. However, a full history should be taken, and skin, lymph nodes, liver and spleen should be examined to check for diffuse or systemic mastocytosis.
In these cases the following investigations may be undertaken:
Most localised forms of cutaneous mastocytosis without symptoms require no treatment.
Treatment for symptomatic patients with mastocytosis includes general measures to avoid triggers for histamine release. Special care should be taken with patients with systemic mastocytosis or diffuse cutaneous mastocytosis, especially if they have elevated serum tryptase, when under anaesthetic or having imaging requiring radio-contrast.
Triggering agents in mastocytosis are physical agents, emotional factors, drugs, venoms, infections, and others.
Infectious diseases with fever
Non-sedating antihistamines such as cetirizine may also be helpful for control/suppression of histamine-related symptoms in mastocytosis. H2 blockers (cimetidine and ranitidine are some examples), leukotriene antagonists, sodium cromoglycate, and omalizumab (off label) are sometimes useful.
Patients with gastrointestinal symptoms from systemic mastocytosis may be treated with H2 histamine antagonists, proton pump inhibitors (eg, omeprazole, lansoprazole, pantoprazole), or oral sodium cromoglycate.
Oral steroids may be used in some cases of systemic mastocytosis. They act as mast cell stabilisers.
Osteoporosis should be treated in patients with this complication of mastocytosis.
In severe cases of systemic mastocytosis or aggressive forms of mastocytosis, the following treatments alone or in combination have been used:
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