Mast Cell Activation Disorders
Other disorders of idiopathic mast cell activation, such as idiopathic anaphylaxis, chronic idiopathic urticaria, intrinsic asthma, and others are less well-understood and warrant further study. Disorders of mast cell activation are not able to be clinically distinguished from mastocytosis, and diagnostic testing for mastocytosis, as described, should be performed. Other factors known to be associated with mast cell activation should be identified and, where possible, appropriately treated; these include hypothyroidism, autoimmunity, neoplastic disease, parasitic infestation, infection, and others.
Laboratory evidence should be sought to support abnormal mast cell mediator release. It has been widely recommended that a serum tryptase level should be drawn within three hours of the beginning of severe symptoms. However, this is not always practical, and it should be noted that this measure has been shown to be unreliable for reasons that are not well understood. (For example, people suffering fatal or nearly fatal anaphylaxis in reaction to foods often show no mature tryptase elevation. In contrast, patients with end-stage renal disease have displayed elevated total tryptase levels.)
Elevated levels of urinary histamine metabolites or of leukotriene E4 are more often positive, but are not specific for mast cell involvement. Recent studies have shown that carboxypeptidase A (CPA) may be elevated in cases where tryptase levels are not. However, the same studies showed that there are cases of apparent anaphylaxis in which neither tryptase nor CPA was elevated.
Treatment of mast cell activation disorders is symptomatic, using all or some of the same mediator-blocking medications used to treat indolent SM---that is, mast cell stabilizers such as cromolyn and/or ketotifen, H1 and H2 antihistamines, leukotriene inhibitors, proton pump inhibitors (if needed for stomach hyperacidity), and where tolerated, a nonsteroidal anti-inflammatory drug. Like those with mastocytosis, some patients with mast cell activation disorders may require higher then normal dosages to control their symptoms. In addition the underlying disorder, if one is present, should be appropriately treated.
Further study and characterization of these disorders is warranted by the number of patients who have not been specifically diagnosed with an explanatory disease in routine testing, but who present clinically with symptoms of a mast cell activation disorder.