Mast cell activation syndrome: Myths and realities.

Background: Mast cells (MCs) have been implicated in a spectrum of allergic, immunologic, and infectious inflammatory conditions that involve different organ systems. MC activation can occur through several different surface receptors other than the well known IgE mediated pathway. Methods: We use two representative case reports from our practice to summarize what is currently known about MCAS disorders (reality) so that the clinician can more easily differentiate these conditions from other complex unexplained conditions that are being associated with MC activation (myth). Results: Many complex MC-related conditions, such as clonal MC diseases, have been well characterized but other MC-related disorders, such as MC activation syndrome (MCAS) and idiopathic anaphylaxis, still remain poorly defined. The current consensus recommendations for a diagnosis of MCAS require clinical symptoms of anaphylaxis that correlate with elevation of a MC activation biomarker(s), which improves with H1-antihistamines. Conclusion: Clinical symptoms of MCAS can overlap with other conditions, including neurogenic disorders, e.g., dysautonomia, which necessitate the importance for the clinician to render an accurate diagnosis so that appropriate treatment is provided.