Mast cells are the main effector cells in allergic diseases. Allergic diseases are mostly a direct result of mast cell mediator release effects, while allergen activation is only one of many triggers for mast cell mediator secretion. Increased mast cell number, high mast cell reactivity, or both can lead to abnormal mast cell activation. Mast cell activated syndrome (MCAS) refers to a group or a\"spectrum\"of mediator-related, symptomatically similar diseases in which mast cells are stimulated by multiple factors. The symptoms and signs of mast cell disease overlap with allergic diseases, but the etiology is different, which requires clinical attention. This article summarizes the research progress on mast cell activation syndrome in recent years thus increase awareness of the differential diagnosis.
肥大细胞是过敏性疾病的主要效应细胞，过敏性疾病的常见表现为肥大细胞被激活后释放介质引起的一系列临床症状。但过敏原激发只是肥大细胞活化的诱因之一。肥大细胞数目增多、高反应性，或者两者兼有，都可以导致肥大细胞异常活化释放颗粒。肥大细胞活化综合征（mast cell activation syndrome，MCAS），泛指肥大细胞受多种因素影响释放介质导致的介质相关的、症状相似的一组疾病。轻者仅表现为皮肤潮红、瘙痒、皮肤风团，重者可出现反复腹痛、低血压、休克，甚至危及生命。肥大细胞疾病患者的症状、体征与过敏性疾病交叉重叠，但病因不同，需引起临床关注。从肥大细胞介质释放的层面理解过敏性疾病，对于疾病预防、治疗及新药研发均有指导意义。.

Systemic mastocytosis (SM) is a heterogeneous disease of the bone marrow, which is characterized by the abnormal proliferation and infiltration of mast cells in one or more organs, such as the skin, bone marrow, digestive tract, liver and spleen. Urticaria pigmentosa is a typical but infrequent manifestation of SM. Other clinical presentations are non-specific, varying from pruritus and hypotension to multiple organ dysfunction, which may be lethal when hemodynamic changes occur, such as the sharp decline in blood pressure observed in the present case. In patients who lack skin lesions, the diagnosis of SM is frequently challenging. The present study reported on a 58-year-old male who presented with episodic flushing and syncope. The patient demonstrated marked neutrophilia and reduced blood potassium concentrations soon after the onset of each episode, which was able to last several hours, ranging from once to four times a year. SM without skin lesions was suspected and confirmed after multifocal bone marrow aspiration, which revealed dense infiltrates of mast cells (≥15 mast cells), with positive toluidine blue and CD117 staining. The present case illustrates the significance of taking SM or mast cell activation syndrome into consideration when unexplained recurrent hypotension or even syncope are observed, care should be taken to exclude differential diagnoses, as some of them may have much poorer prognoses and require alternative treatments.