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Scombroid poisoning, systemic mastocytosis, and hereditary alpha tryptasemia all present with episodes that resemble allergic reactions. Knowledge regarding systemic mastocytosis and hereditary alpha tryptasemia is quickly evolving. Epidemiology, pathophysiology, and strategies to identify and diagnose are discussed. Evidence-based management in the emergency setting and beyond is also explored and summarized. Key differences are described between these events and allergic reactions., Competing Interests: Disclosure The authors declare that they have no relevant or material financial interests that relate to the research described in this article., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Hereditary alpha tryptasemia is an autosomal dominant genetic trait caused by increased germline copies of TPSAB1 encoding alpha-tryptase. Individuals with this trait have elevated basal serum tryptase, and may present with associated multisystem complaints. Both basal serum tryptase levels and severity of clinical symptoms display a gene-dose relationship with TPSAB1, whereby higher tryptase levels and greater symptom severity are correlated with increasing numbers of alpha-encoding TPSAB1. As the functional effects of increased basal serum tryptase and/or altered tryptase gene expression are elucidated, greater insights will be gained into the symptoms associated with hereditary alpha tryptasemia and their potential therapy., (Published by Elsevier Inc.)

Mast cell activation disorders (MCADs) consist of episodic systemic symptoms due to mast cell mediator release. Diagnosis is based on clinical presentation and determination of high levels of tryptase or histamine. Ehlers-Danlos syndrome (EDS) and postural tachycardia syndrome (POTS) frequently coexist. It has been described that individuals with these syndromes can even present symptoms compatible to MCADs, which could represent a new specific phenotype. Preliminary genetic data suggest a role for tryptase in the pathogenesis of MCADs, EDS, and POTS association. Studies with larger samples evaluating clinics, genetics, and histopathology are required to define the real correlation between these 3 clinical entities., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Mastocytosis is a heterogeneous group of neoplasms that involve the clonal expansion of mast cells into one or more organ systems, which typically involves the skin and hematopoietic systems. Systemic mastocytosis consists of a multifocal infiltration of mast cells into various noncutaneous tissue sites, especially the bone marrow. Diagnosis requires tissue confirmation, and algorithms have been developed to assist clinicians in this process. The current classification system focuses on delineating prognostic categories. Therapeutic approaches include symptomatic management, prevention of complications, and, in advanced disease, cytoreductive therapy., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Mastocytosis encompasses a group of clinically and pathologically heterogeneous disorders most commonly involving the skin, which typically takes the form of urticaria pigmentosa. Mastocytosis may also involve other organs, most often bone marrow, followed by gastrointestinal tract, liver, spleen, and lymph nodes. The presence of extracutaneous involvement by mastocytosis is a major diagnostic criterion for systemic disease. However, mast cell infiltrates are often subtle in skin and extracutaneous organs, and the histologic features of mastocytosis at different anatomic sites may be variable. This article reviews the pathologic features and clinical correlates of mastocytosis involving skin and other extramedullary sites., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Mastocytosis is a disease of bone marrow origin histologically characterized by compact tissue infiltrates of atypical mast cells never seen in reactive states. Most patients with mastocytosis have transformed mast cells carrying an activating point mutation at codon 816 of KIT and also show an elevated serum tryptase level. In this article immunophenotypical features of mast cells are described. Based on these features, mast cells are not closely related to other myeloid cells. Using the knowledge on aberrantly expressed antigens by mast cells, the hematopathologist should be able to recognize the disease even in the presence of unusual morphologic findings or an associated hematologic non-mast cell lineage disease., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Tetramer-forming tryptase (hTryptase-β) was recently discovered to have a prominent role in preventing the internal accumulation of life-threatening fibrin deposits and fibrin-platelet clots. The anticoagulant activity of hTryptase-β is an explanation for the presence of hemorrhagic disorders in some patients with anaphylaxis or mastocytosis. The fragments of hFibrinogen formed by the proteolysis of this prominent protein by hTryptase-β could be used as biomarkers in the blood and/or urine for the identification and monitoring of patients with mast cell-dependent disorders. Recombinant hTryptase-β has potential to be used in clinical settings where it is desirable to inhibit blood coagulation., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Mastocytosis is characterized by accumulation of pathologic mast cells in tissues. Most patients with mastocytosis experience mast cell activation symptoms in response to various triggers. The diagnosis of mastocytosis should be made from objective pathologic findings. Modern diagnostic criteria and classification of mastocytosis were proposed in 2000 by an international consensus group and formed the basis of the current World Health Organization (WHO) guidelines, which have been validated to correlate with prognosis and help selection of therapy. In this article, the WHO criteria for diagnosis and classification are summarized and practical aspects to avoid common pitfalls in diagnostic workup are discussed., (Copyright © 2014 Elsevier Inc. All rights reserved.)