A mast cell is a type of white blood cell that is part of the immune system, and it contains many granules that are rich in histamine and several other chemicals. Mast cells are best known for their role in allergic reactions which are initiated by allergens cross-linking high-affinity IgE receptors on their surface. This leads to the release of histamine which typically leads to hives, swelling, hypotension (low blood pressure), bronchospasm with symptom of cough, wheeze and chest tightness, and digestive problems such as diarrhea and vomiting. However, mast cells can cause problems outside of classic allergic reactions as well.
One of the mast cell diseases is mastocytosis, which is characterized by the overproduction of mast cells and CD34+ mast cell precursors. People affected by mastocytosis are susceptible to itching, hives, and anaphylactic shock, caused by the release of histamine from the abundant mast cells. Most cases of mastocytosis are localized to skin, or cutaneous. The most common form of this cutaneous mastocytosis is called urticaria pigmentosa. Urticaria pigmentosa can be diagnosed by identifying dark brown and fixed lesions that forms a hive (or urticates) when scratched. However, urticaria pigmentosa can evolve into systemic mastocytosis which involves the bone marrow and other rare mast cell diseases, such as mast cell leukemia and mast cell sarcoma.
A blood test called a serum tryptase level is the initial screening test for suspected systemic mastocytosis. To confirm the diagnosis a biopsy of the bone marrow or the affected organ to identify an increased numbers of mast cells is needed. There is currently no cure for mastocytosis, but the symptoms are alleviated by a number of medications, such as antihistamines, leukotriene blockers, mast cell stablilizers, corticosteroids, and epinephrine. Other medications that have been used in mastocytosis include proton pump inhibitors to reduce the increased gastric acid production, bronchodilators like Albuterol to reverse bronchoconstriction, calcium channel blockers to reduce mast cell degranulation, and chemotherapy or Gleevec in severe systemic disease.
Another mast cell disorder is mast cell activation syndrome (MCAS) which is characterized by the same symptoms as mastocytosis. In MCAS, however, there is a normal number of mast cells which are defined as “hyperresponsive.” Named as a new diagnosis as recently as 2007, MCAS is often found in patients with Ehlers-Danlos syndrome, postural orthostatic tachycardia syndrome, and idiopathic anaphylaxis. Symptoms can be caused or worsened by triggers such as specific foods and drinks (especially alcohol), temperature extremes, exercise, and emotional stress. Diagnosis of MCAS is often difficult, but laboratory evidence of elevated mast cell mediators such as N-methyl histamine and prostaglandin D2 is helpful, as is a good response to the same drugs used in mastocytosis.
Although rare, mast cell disorders mimic the symptoms of severe allergic reactions and anaphylaxis. Allergy Partners’ board certified Allergist-Immunologists are specialty trained in the diagnosis and treatment of both anaphylaxis and mast cell disorders. To learn more, visits www.allergypartners.com or contact your trusted Allergy Partners physician.
Dr. Sol Drapkin,
Allergy Partners of Chicago