immunology allergic disorders
Mastocytosis and Mast Cell Activation Syndrome
Classification of Mastocytosis
Mastocytosis may be cutaneous or systemic. Cutaneous mastocytosis typically occurs in children. Most patients present with urticaria pigmentosa, a local or diffusely distributed salmon or brown maculopapular rash caused by multiple small mast cell collections. Nodular lesions and plaques can also develop. Less common are diffuse cutaneous mastocytosis, which is skin infiltration without discrete lesions, and mastocytoma, which is a large (1 to 5 cm) solitary collection of mast cells. Cutaneous forms rarely progress to systemic disease in children but may do so in adults. Lesions consist of reddish brown, irregular plaques that urticate when rubbed (Darier sign). By permission of the publisher. From Joe E, Soter N. InCurrent Dermatologic Diagnosis and Treatment, edited by I Freedberg, IM Freedberg, and MR Sanchez. Philadelphia, Current Medicine, 2001. The infant shown here has profuse papulonodular and plaque lesions of urticaria pigmentosa. © Springer Science+Business Media This photo shows reddish brown macules on the back of a school-aged child. © Springer Science+Business Media This image shows yellowish tan to reddish brown macules and papules of urticaria pigmentosa. Image courtesy of Karen McKoy, MD. Urticaria pigmentosa may manifest as reddish plaque-like lesions on the skin. © Springer Science+Business Media Systemic mastocytosis most commonly occurs in adults and is characterized by multifocal bone marrow lesions; it often involves other organs, most commonly skin, lymph nodes, liver, spleen, and/or gastrointestinal (GI) tract. Systemic mastocytosis is classified as Indolent mastocytosis, with no organ dysfunction and a good prognosis Mastocytosis associated with other hematologic disorders (eg, Overview of Myeloproliferative Neoplasms , Aggressive mastocytosis, characterized by impaired organ function Mast cell leukemia, with>20% mast cells in bone marrow, no skin lesions, multiorgan failure, and a poor prognosis Mast cell activation syndrome is characterized by increased and inappropriate activation of mast cells with mediator release but without clonal proliferation or organ infiltration by mast cells ( Classification reference ). The syndrome was originally diagnosed only when mediator release was idiopathic, but it has since been expanded to include release triggered by allergen-specific IgE, certain drugs, or physical factors. Genetic causes are suspected but not proved. Most cases do not involve clonal proliferation of mast cells but are due to a lower threshold for mast cells to degranulate. Mast cell activation syndrome has frequently been associated with The manifestations of mast cell activation syndrome are frequently similar to those of patients with systemic mastocytosis; they include tachycardia, syncope, urticaria, flushing, nausea, vomiting, and brain fog. It is unclear whether mast cell activation syndrome can progress to systemic mastocytosis or another form of mast cell disease and, if so, how many patients are affected. 1.Weiler CR, Austen KF, Akin C, et al: AAAAI Mast Cell Disorders Committee Work Group Report: Mast cell activation syndrome (MCAS) diagnosis and management.J Allergy Clin Immunol144 (4):883–896, 2019. doi: 10.1016/j.jaci.2019.08.023 