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Mastocytosis is a biological disorder that is characterized by an increased number of mast cells in the gastrointestinal (GI) tract, skin, bone marrow, spleen, liver, and lymph nodes.1 Mast cells play a central role in inflammatory processes and in severe reactions such as anaphylaxis.2 There are two common forms of mastocytosis: systemic mastocytosis and cutaneous mastocytosis.
Mastocytosis is a biological disorder that is characterized by an increased numbers of mast cells in the skin, bone marrow, gastrointestinal tract, liver, spleen, and lymph nodes.3
There are two common forms of mastocytosis: systemic mastocytosis and cutaneous mastocytosis.
Systemic mastocytosis (SM) is the more severe form of mastocytosis and is more common in adults than in children. The symptoms vary, as do the organs affected, and can include skin lesions, pain in inner organs, bone pain, diarrhea and vomiting, weight loss, and cardiovascular symptoms. Tryptase levels are increased in the majority of various kinds of SM.4
Cutaneous mastocytosis (CM) is the more benign form of mastocytosis, affecting only the skin. Urticaria pigmentosa is the most common presentation of cutaneous mastocytosis in children and represents 70–90% of the cases. CM is more common in children than adults and is often outgrown.5,6
It is not known how many people are suffering from mastocytosis, but the incidence has been conservatively proposed to be from three to seven new patients per million per year.7 Most cases of mastocytosis have a benign cause over a lifetime. Some cases occur during infancy and early childhood and others appear in adulthood.7 Mastocytosis in childhood may resolve spontaneously and usually only involves the skin; whereas the course in patients with adult-onset disease is normally chronic and includes not only the skin but also systemic symptoms from other organ systems.7
The World Health Organization (WHO) has a consensus on definitions of various forms of mastocytosis and on diagnostic criteria.8
Diagnostic criteria in systemic mastocytosis3
|A. Major criteria|
|1. Histological/immunohistochemical alterations: mast cell aggregates containing more than 15 mast cells in bone marrow sections|
|B. Minor criteria|
1. Cytological alterations: >25% of morphologically abnormal mast cells
2. Detection of c-kit mutations on codon 816
3. Immunophenotypic alterations: expression of CD25 (± CD2) in mast cells from bone marrow, peripheral blood or other organs
4. Total serum tryptase levels persistently >20ng/mL (not applicable if there is a related blood disorder or evidence of acute mast cell release)
|C. Diagnosis of systemic mastocytosis|
a. at least 1 major criterion + 1 minor criterion
b. at least 3 minor criteria
Patients that have mastocytosis may also have acute systemic symptoms, including:8
The most common physical symptoms of mastocytosis involve the skin, liver, spleen, and cardiovascular system. In the case of some chronic systemic symptoms, the gastrointestinal tract and nervous system may also be involved.7 Most patients with this disease will have itchy lesions on their skin.
Tryptase testing can measure the total level of tryptase released by mast cells into the circulation. This enables a healthcare provider to evaluate a person’s baseline tryptase level or any transient increases in the level of tryptase after a suspected allergic reaction. In healthy individuals, the tryptase baseline levels have been reported to range approximately between 1–15 μg/l.4,7 Each individual has its own unique baseline level, which usually is stable over time.7
The prevalence of anaphylaxis in adults with the diagnosis of mastocytosis is reportedly as high as 49%, significantly higher than expected in the general population.1 In children, the risk to develop anaphylaxis is restricted to those with extensive skin symptoms and also a high baseline serum level of tryptase.1