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Mastocytosis

Mastocytosis is a biological disorder that is characterized by an increased numbers 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 (SM) and Cutaneous mastocytosis (CM): SM, the more severe form of the disease, also features elevated levels of tryptase.1,3

Mastocytosis may affect the skin, liver, spleen, or cardiovascular system, though it is possible for the gastrointestinal tract and nervous system to also be involved.1,4,5

Up to 30% of patients with mastocytosis also have venom-induced systemic allergic reactions6

Testing to Identify Patients with Mastocytosis

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.3,8

The World Health Organization (WHO) has a consensus on definitions of various forms of mastocytosis and on diagnostic criteria.4

Diagnostic Criteria in Systemic Mastocytosis4

 

 A. Major Criteria
 1. Histological/immunohistochemical alterations: mast cell aggregates containingmore 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 actue mast cell release)

 C. Diagnosis of Systemic Mastocytosis

1. At least 1 Major Criterion + 1 Minor Criterion

2. At least 3 Minor Criterion

References
  1. Brockow K, Metcale DD. Mastocytosis. Chem Immunol Allergy. 2010; 95: 110-124.  
  2. Valent P, Akin C, Arock M, et al. Definitions, criteria and global classification of mast cell disorders with special reference to mast cell activation syndromes: a consensus proposal. Int Arch Allergy Immunol. 2012;157:215-225. 
  3. Schwartz, LB. Diagnostic value of tryptase in anaphylaxis and mastocytosis. Immunol Allergy Clin N Am. 2006; 26(3):451-463.
  4. Valent P, Akin C, Metcalfe DD. Mastocytosis: 2016 updated WHO classification and novel emerging treatment concepts. Blood. 2017;16;129(11):1420-1427 
  5. Akin C, Valent P, Metcalfe DD. Mast cell activation syndrome: Proposed diagnostic criteria. J Allergy Clin Immunol. 2010;126:1099-1104 
  6. Pawankar R, Holgate ST, Canonica GW, et al. World Allergy Organization (WAO) White Book on Allergy. 2013.  http://www.worldallergy.org/UserFiles/file/WhiteBook2-2013-v8.pdf. Accessed November 2017.  
  7. Valent P. Risk Factors and Management of Severe Life-Threatening Anaphylaxis in Patients with Clonal Mast Cell Disorders. Clin Exp Allergy. 2014;44(7):914-920.  
  8. Komarow et al. Serum tryptase levels in atopic and nonatopic children. J Allergy Clin Immunol. 2009(124): 845-47.