肥大細胞增多症其特徵為全身各器官內有大量的肥大細胞聚集，主要侵犯皮膚，但也 可能侵犯皮膚以外的器官。故根據肥大細胞侵犯的位置不同可將其區分為皮膚性肥大細胞 增多症及全身型肥大細胞增多症。皮膚性肥大細胞增多症，顧名思義，肥大細胞聚集處僅 限於皮膚處，而根據世界衛生組織(World Health Organization, WHO)在2008年更新肥大細胞 增生症的分類與診斷標準中，皮膚性肥大細胞增生症又可被分為四種亞型，其中色素性蕁 麻疹是皮膚性肥大細胞增生症最常見的亞型。在全身性肥大細胞增生症中，肥大細胞會侵 犯皮膚以外的器官，但也有可能合併有皮膚的侵犯。全身性肥大細胞增生症的病患有較高 的機率會產生惡性變化，本案例被誤診為慢性尋痲疹多年，故多年來僅發作時自行服藥緩 解症狀，未曾接受過其他檢查已排除惡性變化的可能，更遑論定期回診追蹤，所以臨床上 當看到病人皮膚病灶並懷疑可能為皮膚性肥大細胞增生症時，需安排進一步檢查以排除全 身性肥大細胞增生症的可能。

Mastocytosis is a rare disorder characterized by marked mast cells infiltrate in the skin and/ or other organs.It can be subdivided into two subtypes: cutaneous mastocytosis and systemic mastocytosis. Cutaneous mastocytosis is limited to skin and it includes four subtypes among which urticaria pigmentosa is the most common. Systemic mastocytosis is characterized by mast-cell infiltrationin multiple extracutaneous organs with or without skin involvement and ittends to have a greater risk of malignant transformation.Most patients, clinically suspected as mastocytosis with skin lesions, should undergo examination to exclude the possibility of systemic mastocytosis.We present a clinicalcase of a 22-year-old patient with urticaria pigmentosa.