Patients with mast cell activation disorders present with recurrent symptoms of mast cell activation, in combination with objective evidence of mast cell-mediator release. Two mast cell activation disorders have been proposed and defined:
●Monoclonal mast cell activation syndrome (MMAS)
●Mast cell activation syndrome (MCAS)
This topic will review the classification of mast cell disorders and then focus on MMAS and MCAS, describing the clinical manifestations, evaluation, diagnosis, and treatment of these disorders. By the time a mast cell disorder is considered, patients have typically undergone evaluation for a wide array of disorders, both allergic and nonallergic. Disorders that can mimic allergic reactions and anaphylaxis are discussed separately. (See "Differential diagnosis of anaphylaxis in children and adults".)
CLASSIFICATION OF MAST CELL DISORDERS
Mast cell disorders can be broadly divided into three types: primary, secondary, and idiopathic (table 1). All of these disorders present with signs and symptoms of mast cell activation and differ in severity and involvement of various organ systems. Within this framework, monoclonal mast cell activation syndrome (MMAS) is best classified as a primary mast cell disorder, while mast cell activation syndrome (MCAS) is considered an idiopathic disorder.