Mastocytosis
What is it?
Mastocytosis is a rare disease characterized by abnormal proliferation and accumulation of mast cells in different organs and tissues. Mast cell is a cell involved in the genesis of allergic, hypersensitivity and anaphylactic reactions and is normally found in bone marrow (small amount), connective tissue and blood vessels.
The pathology is mainly due to the proliferation and abnormal release of mediators from mast cells, such as histamine, heparin, leukotrienes, and various inflammatory cytokines. Histamine causes many symptoms that may resemble allergic manifestations. Significant organ infiltration can cause functional impairment and bone marrow failure.
Mastocytosis is a rare disease with a slight predominance in the male sex (the male-to-female ratio has been reported to vary from 1:1 to 1:3). Not being a hereditary condition, it can occur at any age and be present even at birth.
Mastocytic disorders can be different in nature. Mastocytosis is defined as:
- cutaneous mastocytosis, when the mast cell infiltrate is limited to the skin. It is most common in children: about 50% of affected children have typical skin lesions within the first 6 months of life, but most of them (90%) heal spontaneously during adolescence;
- systemic mastocytosis, when mast cells proliferate in other organs and tissues such as bone marrow, gastrointestinal tract, lung, liver, spleen, and lymph nodes. Systemic mastocytosis is more common in adulthood and usually occurs after the second decade of age, with heterogeneous manifestations. In the context of systemic mastocytosis, we speak of the indolent form in the case of no organ dysfunction or blood-chromocytometric changes, while in the case of symptoms of organ infiltration or bone marrow failure we speak of aggressive mastocytosis.
Cutaneous mastocytosis and indolent systemic mastocytosis are by far the most frequent forms. There is also an extremely rare form of MastCellular Leukemia. The evolution of a form of mastocytosis into a more aggressive one is possible but infrequent.
Which are the symptoms?
In cutaneous mastocytosis, the most common symptom is itching. In systemic mastocytosis, skin lesions may be present but also completely absent; the other main symptoms are extremely heterogeneous:
- flushing or redness of the face
- headaches
- fatigue
- drops in blood pressure
- nausea
- diarrhea
- abdominal pain
- bone involvement (osteoporosis)
In some cases, the patient may be totally asymptomatic. Among the most striking manifestations of mastocytosis are anaphylactic reactions: severe sudden drops in blood pressure, respiratory distress, abdominal pain, and fainting requiring urgent access to emergency rooms for prompt treatment. Symptomatic episodes can be triggered by stimuli of various types: food, drugs, insect bites, mechanical, physical, thermal and emotional stresses.
How is it diagnosed?
Mastocytosis is usually diagnosed by analysis of skin lesions associated with the disease. In cases without overt skin symptoms, diagnosis is more difficult and often comes following allergologic evaluations performed for anaphylactic episodes. In any case, the disease is often not recognized until many years after it occurs (median time to diagnosis 3-5 years). Examination of bone marrow samples is usually recommended in adult patients (when certain suspicion criteria are met), whereas in children with cutaneous mastocytosis it is usually not necessary. Laboratory tests can help in diagnosis, especially measurement of tryptase (a protein produced by mast cells) levels in the blood. Since osteoporosis is common even in younger patients, after diagnosis it is important to assess bone density by a test called Bone Mineralometry (BMM).
How is it treated?
Currently, there is no specific treatment to cure mastocytosis permanently. Most pediatric cases heal spontaneously and require no treatment. Treatment of mastocytosis must be individualized and prescribed strictly in the specialist setting because one of the most important goals is to prevent and/or control the symptoms of the disease by blocking the release or action of chemicals produced by mast cells. Some patients with systemic mastocytosis may have potentially fatal anaphylactic reactions; adrenaline is a life-saving drug in such cases, so all patients should always carry an adrenaline self-injection device for use in an emergency. Phototherapy, which involves exposing the skin to ultraviolet (UVA) light, is used for skin manifestations and itching; pro-drugs such as psoralens can be used to increase the effectiveness of phototherapy. Gastroprotectant drugs are sufficient to relieve gastrointestinal symptoms. The so-called membrane stabilizers (such as sodium cromoglycate and ketotifene) are drugs that hinder the release of chemicals by mast cells.
Other drugs (such as antihistamines and corticosteroids) limit the adverse effects caused by these substances. Bone pain related to altered calcium metabolism and thus the onset of osteoporosis can be treated with calcium, vitamin D3, or bisphosphonates.
For more severe forms of mastocytosis, immunomodulatory and chemotherapeutic drugs (such as midostaurin, cladribine, and hydroxyurea) or biologics (interferon) are also available and are used to counteract the growth of tumor mast cells. In selected cases, next-generation drugs, such as tyrosine kinase inhibitors (imatinib, dasatinib), may be useful in controlling the disease.
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