Glossary of mast cell related terms: M-O

Mast cell: white blood cells with important roles in allergy, anaphylaxis and immune defense that live in tissues and only briefly circulate in the blood; also called mastocytes

Mast cell activation: a change in mast cell behavior that occurs following exposure to a trigger that may indicate allergy or infection; a state in which mast cells release mediators, both through degranulation and through secretion; in some instances, culminating in anaphylaxis

Mast cell disease: a disease that occurs due to fundamental error in mast cell proliferation or activation physiology

Mast cell disorder: used synonymously with mast cell disease

Mast cell leukemia: a very aggressive mast cell disease marked by massively excessive proliferation of mast cells, culminating in progressive organ failure

Mast cell sarcoma: a very aggressive mast cell disease that presents as a connective tissue tumor and progresses to mast cell leukemia

Mast cell stabilizer: a medication that decreases the likelihood of mast cell degranulation and mediator release

Mastocytic enterocolitis: the phenomenon of having too many mast cells in the GI tract; originally described as more than 20 mast cells/ high power field, but there is no consensus on how many mast cells in a field is too many

Mastocytoma: a benign mast cell tumor. Most frequently occurs on skin, but can occur elsewhere in the body.

Mast cell activation disease (MCAD): usually a catchall term for mast cell diseases, although some people exclude cutaneous mastocytosis from this category

Mast cell activation disorder (MCAD): an alternate term for mast cell activation syndrome (MCAS); a non-proliferative mast cell disease that is usually diagnosed by detecting an elevation in mast cell mediators

Mast cell activation syndrome (MCAS): a non-proliferative mast cell disease that is usually diagnosed by detecting an elevation in mast cell mediators; occurs secondary to a known condition or idiopathically, in which no primary condition is identified; “primary” mast cell activation syndrome has its own name, MMAS

Mediator: a molecule released from a cell that has effects on the environment outside the cell; mast cells release dozens of mediators

Monoclonal mast cell activation syndrome (MMAS) : a mast cell disease diagnosed when a patient meets some criteria for SM but not enough for an SM diagnosed

Monophasic anaphylaxis: an anaphylactic event in which symptoms resolve following administration of medication and do not recur at a later time

Mutation: a change in the genetic sequence that can affect the way a gene is expressed, or in the way its gene product is made or functions

Myeloid: concerning cells that develop into granulocytes, monocytes, platelets or erythrocytes

Myeloproliferative neoplasm: a disorder caused by aberrant proliferation of a myeloid cell line, such as SM, myelofibrosis, essential thrombocythemia or polycythemia vera, among others

Neoplasm: an abnormal cell

N-methylhistamine: a breakdown product of histamine; can be tested for to assess mast cell activation

Oral allergy syndrome: An IgE reaction to raw fruits and vegetables that causes itching and swelling in the mouth and throat.

Orthostatic hypotension (OH): reduction of systolic blood pressure of more than 20 mm Hg or diastolic blood pressure of more than 10 mm Hg within three minutes of standing.

Orthostatic intolerance (OI): symptoms that occur when transitioning to a standing position