上一篇概論裡面,沒有多加著墨致病原理,除了實在內容太硬以外(怕看了睡著),其實是連Thomas Mettang大師自己也無法斷定,什麼是根本的原因,尤其慢性腎臟病患者,有時候也伴隨著其他容易癢的疾病,因此狀況十分複雜。
目前假想的理論是,1.某種物質的刺激,2.經過某些情況的放大,3.最後腦部裡接受到癢的感覺。
1. 會引起刺激的物質
包含:副甲狀腺素(iPTH)、組織胺(Histamin)、Tryptase、外來物質(xenobiotica)或尿毒素(uremic toxin)、細胞激素(cytokines)、以及發炎反應。
副甲狀腺素一向被認為和癢有關係,但是,如果將副甲狀腺素打到人的皮下去,並不會產生癢的反應,而如果將透析搔癢症的患者做皮膚切片,這皮膚組織裡面也沒有看到副甲狀腺素,唯一的證據只有:如果用手術切除了副甲狀腺,來治療副甲狀腺機能亢進,患者的癢確實會好轉。
組織胺(Histamin)、Tryptase、細胞激素(cytokines)、以及發炎反應等等,都是造成皮膚癢的過程之一,皮膚為什麼會癢,是因為肥大細胞(mast cell)受到某種刺激,而放出了它裡面的細胞激素、組織胺(Histamin)、以及Tryptase等等,這些物質進一步引起各種的反應,而有了癢的感覺,在透析搔癢症的患者身上,也會看到這些物質增加。一般我們常用的第一線止癢藥物,就是抗組織胺,可惜效果常常不一致,有人有效,有人沒效。
外來物質(xenobiotica),最常被爭論的是維他命A、以及轉移性的微小鈣化(metastatic micro-calcification),這些刺激物也常被提到。
2. 經過某些情況的放大
指的是“乾燥的皮膚”,這算是增強癢感的煽動者,因為腎臟病患的皮膚常常會乾燥(原因在上一篇略有提到),但是有皮膚乾燥的人,不一定會癢;但是只要會癢的患者,擦了保濕乳液改善皮膚乾燥,癢的感覺就會改善。因此,目前認為,乾燥的皮膚是推波助瀾的幫兇、而非真正的兇手。
3. 腦部裡接受到癢的感覺
是 μ-受器與 κ-受器之間的不平衡,傾向 μ-受器太活化、而 κ-受器太被壓抑了。因此這兩種受器相關的藥物治療,也被研究嘗試過,效果如上一篇所述。
治療建議流程
圖中的第一步,就是排除其他會造成癢的原因,個人經驗中,糖尿病患者血糖沒控制好,可以說是“其他原因”裡面最常見的,研究顯示,飯後血糖越高,糖尿病患者越容易癢,而背後的機轉,和皮膚的黴菌感染、皮膚乾燥以及循環不佳有關係。因此,如果是腎臟病患合併有糖尿病,第一步,先把血糖控制好!
個人經驗
第一步,先做好皮膚的保養,也就是保濕乳液的擦拭,一天至少兩次以上,若天氣冷,洗澡時少用肥皂,洗澡用水也不要太燙,這些都是讓皮膚保持有足夠的油脂,來保護皮膚水份不要流失。
第二步,足夠的透析,控制好血中鈣與磷,進而讓副甲狀腺素數值控制在正常範圍,還有血糖的控制也非常重要!請糖尿病患者一定要注意,時時測量血糖,才能保身體健康。
第三步用藥,抗組織胺是最常用的藥物,有效就有效,沒效再想別的藥物。Gabapentin效果算是不錯,但是如果過量的話,副作用有嗜睡、水腫等等,尤其是嗜睡,嚴重的話容易造成年紀大的人頭暈、步態不穩、跌倒、受傷、甚至骨折等等,這篇回顧性文章,有建議劑量,或許可嚐試看看這樣低劑量的用法。另外,pregabalin的副作用機率較低,可能是更安全的選擇。
第四步,走到這裡還非常癢的患者,就得用不一樣的方法了,如上圖所示,但我相信,前三步就能解決絕大部分的問題了。
在考慮任何治療之前,請務必和照顧您的醫師討論,切勿以身試藥。
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