紫質症 (Porphyria)

http://www.nytimes.com/2016/12/09/well/live/think-like-a-doctor-the-builders-blisters-solved.html

The New York Times 這期的病例是罕見疾病，又是常常耳聞的困難診斷疾病。吸引人從頭讀下去，讀起來真像偵探辦案一樣。

這是在美國榮民醫院的一位64歲男性患者，喜歡露營，是工程承包商，20年病史的偶發性手上手泡，不明原因。

The patient’s hands showed a blistering rash.

一次就診時，不經意的向實習醫生說起手上這些20年不間斷發作的水泡。一開始interns，和主治醫師認為可能是contact dermatitis, or allergic reaction。但是，了解病史後又被排除，只好把病人轉介給皮膚科。但是，這位認真主治醫師去查UpToDate: Rash chapter，發現這和porphyria cutanea tarda 皮疹很像。

Glowing Urine

The patient’s urine (right) glowed orange under a Wood’s lamp, while normal urine (left) glows blue.

於是經由尿液送檢，和用wood's lamp觀察尿液呈現orange (purple)，幾乎就要證實是這個疾病。然而，引發的原因是什麼(trigger)？測HCV也沒有，經過查閱過去的病歷，發現曾有很高的血液鐵質存在，但是之前醫師也沒有進一步處理。這時候，誘發原因：hemochromatosis，在抽血檢查後，就呼之欲出了。在這深秋的季節，患者的皮膚有點過度的tanned，原本以為是喜歡露營曬太陽所致，原來也是因為porphyria發作，導致皮下有Hb未分解產物過多造成。難怪患者說在夏天時，皮膚特別容易有水泡。

The rash was from: Porphyria cutanea tarda

Which was in turn caused by: Hereditary hemochromatosis (‘Bronze Diabetes’)

About the Diagnosis

The porphyrias are a group of diseases caused by a problem in the breakdown of hemoglobin, the oxygen-carrying part of red blood cells. The name comes from the Latin word for purple (porphyros), because with some forms of this disease, the unbroken-down parts of hemoglobin are eliminated from the body in the urine, and those chemicals can make the urine turn purple when exposed to sunlight.

The rest of the name highlights the disease’s most characteristic qualities: It affects the skin (cutanea) and it appears late in life (tarda). In P.C.T., the particular components of hemoglobin that are not fully broken down migrate to the skin, where they cause a blistering sore when exposed to sunlight.

結局：
患者開始看血液科，排除過多的鐵質。注意防曬，之前就是因為有習慣擦防曬乳所以porphyria發作得並不明顯。患者也想把過多的血捐給紅十字會，但是紅十字會不收有這樣疾病人的血液。