Case 1：A 25-year-old man is brought to the emergency room by ambulance after a motor vehicle collision. He is lucid but has severe bleeding from his leg. His wife is with him and reports that the patient is generally healthy, although he had several bouts of 「lung and ear infections」 as a child. He also has a history of milk allergy and periodically suffers from diarrhea. In the ER he is given 1 unit of type-matched RBCs. Soon afterward he develops a red, itchy rash over most of his body and begins to have difficulty breathing. His blood pressure drops despite continuous fluid infusion.
案例1：一名25歲的男子在車禍後被救護車送往急診室。他神志清醒，但腿部有嚴重出血。他的妻子報告說，病人總體健康，小時候有幾次「肺部和耳朵感染」。他還有牛奶過敏史，並定期出現腹瀉。在急診室，他被給予1個單位的類型匹配紅細胞。不久之後，全身出現紅色皮疹伴瘙癢，呼吸困難。儘管不斷地輸液，仍有血壓下降。
1 What is the most likely cause of this patient’s repeated infections and allergic reaction to the blood transfusion?
This patient is having an anaphylactic reaction. IgA is a common component in blood products. He likely has hereditary IgA deficiency, and therefore has developed IgG Ab against IgA. IgA deficiency can occur as isolated syndrome or may involve concurrent IgG deficiency.
IgA缺乏症診斷
出現突發嚴重過敏反應+既往過敏史（題幹中牛奶過敏）+多發感染（題幹中肺部和鼻竇感染），多半繼發性IgG缺乏。
2 What is the next step in management of this condition?
Due to severe anaphylactic reaction to the transfused blood products, discontinue transfusion and administer epinephrine injection to counteract the bronchospasm and vasodilation.
治療措施
停止輸血+腎上腺素皮下注射，以緩解過敏所致的呼吸困難。
3 What is the cause of patient’s milk allergy?
In the absence of intestinal IgA, large proteins are mostly entering the bloodstream as a whole. An IgG Ab to these proteins can cause an allergic reaction.
IgA缺乏致過敏原因
IgA多在腸道內表達，缺乏後可致大蛋白入血，引起蛋白抗體IgG產生，出現過敏反應。
Case 2: A 20-year-old woman returns from a day hike in a densely wooded area and develops a rash that evening. The next day she presents to her physician. The patient has never developed a rash like this before an has hiked in this wooded area several times. Physical examination reveals that the rash is mostly on the legs, arms and hands—areas the patient says 「were not covered by clothing」. She is afebrile.
案例2：一名20歲的女性在茂密的樹林裡徒步旅行了一天，當天晚上出現皮疹。既往從未出現過類似皮疹，以前他曾在這片林區徒步旅行過幾次。體格檢查發現皮疹主要出現在腿、手臂和手的部位，無發熱。
1 What is the most likely diagnosis?
Photodermatitis secondary to poison ivy. The rash is characterized by vesicles<5mm in diameter. Vesicles often coalesce in severe rashes.
植物性皮炎
繼發於毒藤類植物接觸，特點為水皰直徑<5mm，但嚴重皮疹時水皰多合併成片狀。
2 Which type of hypersensitivity reaction is occurring in this patient?
Type IV (delayed or cell-mediated) include contact hypersensitivity from poison ivy, transplant rejection, hypersensitivity pneumonitis, granulomatous hypersensitivity reactions, and the TB skin test.
所屬超敏反應類型
IV型遲髮型超敏反應，包括毒藤類過敏、移植物排斥、高敏性肺炎、結核皮試等。