瘙癢和撓癢有什麼科學依據嗎?大綱

The experiment was not for the squirmish. Volunteers were made to itch like crazy on one arm, but not allowed to scratch. Then they were whisked into an M.R.I. scanner to see what parts of their brains lit up when they itched, when researchers scratched them and when they were finally allowed to scratch themselves.

首先要申明的是，做這個實驗可不是要存心折磨人——研究人員通過某些手段致使志願者們一條手臂癢得發瘋，卻不允許他們用任何方式撓癢。然後再將他們送入磁共振(MRI)掃描儀，觀察他們感到癢癢時，當研究人員幫他們撓癢，以及當他們終於得以自己撓癢時，他們的大腦中分別有哪些部位處於活躍狀態。

The scientific question was this: Why does it feel so good to scratch an itch?

這項研究所要解決的科學問題是：爲什麼撓癢的感覺這麼爽？

"It's quite intriguing to see how many brain centers are activated," said Dr. Gil Yosipovitch, chairman of dermatology at the Temple University School of Medicine and director of the Temple Center for Itch (he conducted the experiment while working at Wake Forest School of Medicine). "There is no one itch center. Everyone wants that target, but it doesn't work in real life like that."

“觀察有多少大腦中樞受到激活，這差事相當有趣，”美國天普大學醫學院(Temple University School of Medicine)的皮膚學系主任，天普大學瘙癢中心(Temple Center for Itch)主任吉爾·楊斯波維奇(Gil Yosipovitch)博士說。（他在威克森林大學[Wake Forest School of Medicine]工作時已經開展這項實驗）。“大腦中並沒有一個專門的瘙癢中樞。當然大家都希望能有這樣一個靶標可以用來對付瘙癢，可現實並不總能盡如人意。”

Instead, itching and scratching engage brain areas involved not only in sensation, but also in mental processes that help explain why we love to scratch: motivation and reward, pleasure, craving and even addiction. What an itch turns on, a scratch turns off — and scratching oneself does it better than being scratched by someone else. The study results were published in December in the journal PLOS One.

與人們的期望相反，瘙癢和撓癢不僅與腦部感覺區有關，還涉及了某些心理過程，譬如：動機和獎賞、愉悅、渴求乃至成癮等，這就從一定程度上解釋了人們喜歡撓癢的原因。撓癢可以關閉那些被瘙癢激活的腦部活動，而且，自己撓癢癢的效果往往優於別人代勞。這些研究結果發表在12月的《公共科學圖書館：綜合》雜誌(PLOS One)上。

Itching was long overshadowed by pain in both research and treatment, and was even considered just a mild form of pain. But millions of people suffer from itching, and times have changed. Research has found nerves, molecules and cellular receptors that are specific for itching and set it apart from pain, and the medical profession has begun to take it seriously as a debilitating problem that deserves to be studied and treated.

長期以來，無論是在研究領域還是治療領域，瘙癢作爲一個課題總是被另一個課題——疼痛搶盡了風頭，甚至，人們一度以爲瘙癢只是疼痛的一種較爲溫和的形式。然而，全球遭受瘙癢之苦的患者已達數百萬之多，時代也已經發生了變遷。研究發現，瘙癢具有其特異性的神經、分子和細胞受體，這將它與疼痛區分開來。醫學界已經認識到瘙癢也可以削弱人的身體，並開始將其作爲一個值得研究和治療的問題認真對待。

Within the last decade, there has been a flurry of research into what causes itching and how to stop it. Along with brain imaging, studies have begun to look at gene activity and to map the signals that flow between cells in the skin, the immune system, the spinal cord and the brain.

在過去的十年裏涌現出了一系列的研究，探討了引起瘙癢的原因以及如何才能阻止瘙癢。在腦成像技術的幫助下，現在的研究日益關注有關基因的活性，並試圖去捕捉和描述那些在皮膚細胞、免疫系統以及脊髓和腦之間流動的信號。

The concern is not so much the fleeting nastiness of mosquito bites and poison ivy, but the unending misery caused by chronic itching — the kind that won't go away, that torments people night and day and very often resists remedies like antihistamines and cortisone cream.

研究所關注的重點並非是像蚊蟲叮咬和毒葛那種轉瞬即逝的小麻煩，而是因長期慢性瘙癢引起的無休止的痛苦——它揮之不去，日日夜夜折磨着人們，而且往往對抗組胺藥物和可的鬆軟膏等療法都具有耐受性。

For the first time in the United States, itching research and treatment centers have opened: Temple's in September, in Philadelphia, and Washington University's Center for the Study of Itch, in 2011, in St. Louis.

9月在費城開辦的天普大學瘙癢中心以及2011年在聖路易斯開辦的華盛頓大學(Washington University)瘙癢研究中心(Center for the Study of Itch)是美國開辦的第一批瘙癢研究和治療中心。

"Itch is now where pain was probably 20 years ago," said Dr. Lynn Cornelius, chief of the dermatology division at Washington University School of Medicine. "It used to be lumped together with pain."

“今天，人們對瘙癢的重視程度與20年前對疼痛的重視程度相仿，”華盛頓大學醫學院(Washington University School of Medicine)皮膚病學系的主任琳內特·科爾內留斯(Lynn Cornelius)博士說。“過去，人們總是把它與疼痛混爲一談。”

But now, she said, there is more interest in itching and in sorting out its different types, and more research money being spent on it.

但現在，她繼續說，人們對瘙癢及其分類更感興趣，也願意在這方面投入大筆的研究資金。

"The science has to lead to treatment, I believe," Dr. Cornelius said. "If that happens, it will translate to better and better, more targeted therapies, so clinicians won't just look upon someone itching as someone who needs antihistamines."

“我堅信，科學的發展必將導致治療領域的進步，”科爾內留斯博士說。“若果真有這麼一天，科研成果將轉化爲更好，也更有針對性的療法，這樣，醫生就不至於只能向受到瘙癢困擾的患者處方抗組胺藥物了。”

Scratching, and therefore itching, appear widespread in the animal kingdom — though no one knows for sure why animals claw, bite or peck themselves, or scrape against trees or fences.

搔癢行爲在動物世界裏普遍存在。儘管沒有人能確切地知道動物爲什麼要去抓、咬或啄自己，或將身體在樹木或柵欄上摩擦，但人們推測，這很可能是因爲它們也會感到瘙癢。

Even fruit flies engage in "robust grooming behaviors" that look a lot like scratching when they are infected with mites, said Diana Bautista, an assistant professor of cell and developmental biology at the University of California, Berkeley. Her research includes studying various strains of itchy mice that are models for human ailments.

即使是果蠅這種低等生物，在它們感染蟎蟲時，也會出現一種跟搔癢看起來頗爲相似的“強力梳理行爲(robust grooming behaviors)”，加州大學伯克利分校(University of California, Berkeley)的細胞和發育生物學助理教授戴安娜·鮑蒂斯塔(Diana Bautista)說。此外，她的研究還包括多種品系的瘙癢小鼠，它們都是業已建立的不同人類疾病的模型小鼠。

"I have a collection of movies showing different animals scratching," Dr. Bautista said. "I'm hoping they will help me determine if there is a difference between itch-evoked scratching versus wiping and other behaviors in diverse species."

“我還收集了許多介紹不同動物搔癢行爲的視頻資料，”鮑蒂斯塔博士說，“我希望它們可以幫助我確定在不同的物種中，瘙癢引起的撓癢行爲與擦拭及其他行爲之間是否存在差異。”

One of her favorite videos shows a seal lying on the beach, briskly rubbing its head with a flipper.

她最喜歡的一段視頻展示了這樣的景象：一隻海豹躺在沙灘上，輕快地用自己的鰭狀肢摩擦着頭部。

In people, there are different types of itching. The most familiar type, from a mosquito bite or hives, occurs when cells in the skin release histamine, which causes nerves in the skin to fire off signals to the spinal cord and brain. Antihistamine pills or creams usually bring relief.

在人類當中，存在着多種不同類型的瘙癢。人們最熟悉的一種因蚊蟲叮咬或蕁麻疹引起，此時皮膚細胞釋放出組胺，引起皮膚中的神經產生信號，並傳導到脊髓和大腦。抗組胺片劑或藥膏通常可以緩解其症狀。

But antihistamines are often no help to people with chronic itching, which can be caused by skin diseases like eczema or psoriasis, kidney or liver failure, dry skin, an overactive thyroid gland, certain cancers, and pinched or damaged nerves. And the itching from psoriasis almost certainly has a different mechanism from that caused by a pinched nerve.

然而，這些藥物對慢性瘙癢患者往往就愛莫能助了。溼疹或銀屑病（牛皮癬）等皮膚病、腎臟或肝臟衰竭、皮膚乾燥、甲狀腺功能亢進、某些癌症以及神經受到擠壓或損壞都可能導致慢性瘙癢。而且幾乎可以肯定的是，因銀屑病引起的瘙癢與神經受壓引起的瘙癢具有不同的機制。

"It's a very hot area," Dr. Cornelius said. "It's a huge clinical problem and a huge unmet market."

“這是一個非常熱門的領域，”科爾內留斯博士說，“它既是重大的臨牀問題，又提供了一個需求遠遠未得到滿足的巨大市場。”

Recent research has shown that substances other than histamine, released from inflammatory cells, are involved in chronic itching, along with three different types of nerve cells, Dr. Bautista said. Drug companies are trying to find ways to block those substances.

鮑蒂斯塔博士介紹道，最近的研究表明，除了組胺，炎性細胞還釋放出了其他一些與慢性瘙癢有關的物質，此外，還有三種不同類型的神經細胞也參與了這一過程。製藥公司正致力於尋找可阻斷這些物質的方法。

"Before, the focus was on next-generation antihistamines," Dr. Bautista said. "Now, it's on new molecular and cellular targets to develop new therapies. The pharmaceutical industry is recognizing that they have to go beyond antihistamines."

“以前，他們的研發重點一直是新一代的抗組胺藥物，”鮑蒂斯塔博士說，“現在，他們則瞄準了新的分子和細胞靶標來開發新的療法。醫藥行業已經認識到，他們不能再侷限於抗組胺藥物，必須有所超越。”

But pain pathways have to be dissected in minute detail if new targets are to be found. Many researchers say that one of the most important advances in the field was reported in the journal Nature in 2007 by a Washington University team led by Zhou-Feng Chen, who is now director of the itch center. Working with mice, his team was studying receptors, molecules on cells that respond to certain chemical signals to change the cells' behavior.

但是，要找到新的靶標，就必須將疼痛通路的每個微小的細節都剖析清楚。現任華盛頓大學瘙癢中心主任陳宙峯(Zhou-Feng Chen)領導團隊利用小鼠研究了可對特定的化學信號作出反應，並改變細胞行爲的細胞表面受體和分子。這一2007年發表在《自然》雜誌(Nature)上的研究被衆多研究人員一致認爲是該領域最重要的進展之一。

The group was the first to find a receptor in the spinal cord that was specific for itching, called gastrin-releasing peptide receptor, or GRPR. The discovery helped to prove that signals for itching and pain travel on different pathways.

該小組首次在脊髓中發現了瘙癢特異性受體，稱爲胃泌素釋放肽受體(gastrin-releasing peptide receptor)，簡稱GRPR。這一發現有助於證明瘙癢和疼痛的信號傳導途徑並不相同。

In an interview, Dr. Chen said that mice without the receptor — or with the receptor blocked by a drug — did not itch. Nor was the group without a receptor harmed by the lack of it.

陳博士在接受採訪時表示，不具備該受體，或該受體被藥物阻斷的小鼠就不會產生瘙癢的感覺。且無受體組的小鼠並未因此而受到損害。

"If you block function of this receptor alone, you pretty much stop chronic itching," he said.

“僅僅阻斷該受體的功能，就幾乎足以給慢性瘙癢畫上句號，”他說。

The receptor is present in humans, too, and Dr. Chen said it might be possible to develop a drug that would block it.

該受體也存在於人體之中，陳博士認爲未來有望開發出一種可以阻斷它的藥物。

For many patients, new treatments cannot come soon enough.

但對於大多數患者而言，新療法問世的速度還不夠快。

Chronic itching becomes more common with age. One reason is that older people often develop dry skin, but Dr. Yosipovitch said the itching also might occur because certain nerves in the skin deteriorate — nerves that transmit pain and inhibit itching. "Then itch kind of pops out," he said.

隨着年齡的增長，慢性瘙癢在人羣中日漸常見。其原因之一是老年人往往存在皮膚乾燥。但楊斯波維奇博士認爲，皮膚中某些神經的受損也可能造成瘙癢——這些神經原本負責傳導疼痛並抑制瘙癢，它們一出毛病，“瘙癢就蹦了出來，”他說。

Aging monkeys have provided some clues. When Dr. Yosipovitch was still at Wake Forest, he and his colleagues noticed older female macaques scratching their backs and lower limbs, the same spots where older people tend to itch.

衰老的猴子爲此提供了一些線索。早在楊斯波維奇博士在維克森林大學工作時，他和同事們就發現老年雌性獼猴會抓撓自己的背部和下肢——老年人經常感到瘙癢的也是同樣的部位。

They sent samples from the monkeys to Dr. Chen, who found extra activity in the skin and spinal cord from the gene that produces GRPR, the itch receptor. Why the gene becomes more active with aging is not known, but this finding in a primate supports the idea that the receptor is a good target for new drugs in people, Dr. Chen said.

他們將這些猴子的樣本送到了陳博士的實驗室。陳博士他們隨後發現，在這些猴子的皮膚和脊髓裏，表達瘙癢受體GRPR的基因過度活躍。陳博士表示，目前尚不清楚該基因爲什麼會隨着衰老而趨於活躍，但這一在靈長類身上得到的發現支持這一觀點：該受體是研發治療人類瘙癢的新藥的良好靶標。

Many older people have trouble with itching in hard-to-reach spots on the back, between or just below the shoulder blades.

許多老年人都存在這樣的麻煩：瘙癢的部位正好位於後背上肩胛骨下方或其之間的位置，他們的手很難夠着。

"It drives them crazy," said Dr. Cornelius, at Washington University. They rub against door jambs, stockpile back scratchers, and enlist others to scratch them.

“這簡直要把他們逼瘋了，”科尼利厄斯博士在華盛頓大學時說。他們只好用身體摩擦門框，大量購置癢癢撓，並要求其他人來幫他們瘙癢。

The condition has a name, notalgia paresthetica, and is often associated with spine and disk problems that pinch or damage nerves. The skin in the itchy spots may darken.

這種疾病名爲感覺異常性背痛(notalgia paresthetica)，它通常與脊柱和椎間盤出現問題，壓迫或損傷了神經相關。癢點處的膚色有可能會變暗。

"Some neurologists, I would say the majority, do not know about this," Dr. Yosipovitch said.

“一部分神經科醫生，甚至可以說其中的大多數都不知道這一點，”楊斯波維奇博士說。

He and other doctors have prescribed various remedies — numbing patches, sometimes along with the hot-pepper ingredient capsaicin; Botox injections; pills like gabapentin that affect nerve transmission; and physical therapy to change posture. Often, it is possible to find something that helps.

他和其他醫生也曾處方過多種治療方法：止癢貼片，有時輔以辣椒中的成分辣椒素；注射肉毒桿菌毒素(Botox)；加巴噴丁(gabapentin)等可影響神經傳導的藥劑；物理治療等，試圖改善瘙癢症狀。但基本上沒有一種見效。

Dr. Yosipovitch said many patients found their way to him only after seeing multiple doctors who could not help and who sometimes misdiagnosed their problems as mental rather than physical.

楊斯波維奇博士說，許多患者都是在拜訪過衆多表示愛莫能助的醫生（其中甚至有人將身體的瘙癢誤診爲心理疾病）後才找上了自己。

"They're not crazy," he said.

“他們當然不是腦筋出了問題，”他說。

One of the patients was a boy who had scratched his arms and legs raw. Unable to find a cause or a treatment that worked, doctors had referred him and his family to a psychiatrist.

其中一名患者是個男孩子，他把自己的手臂和腿都抓撓得破了皮。醫生找不到病因，也沒什麼有效的療法，只好將他轉診給了心理醫生。

In an interview, the patient, Joshua Riegel, now 18, said, "They said I was doing it to manipulate my parents." Thus began what he calls "that weird part of my life where they thought I was mentally ill."

這位名叫喬舒亞·裏格爾(Joshua Riegel)的患者現年18歲，他在接受採訪時說：“他們都說我這樣是故意的，目的是爲了作弄我的父母。”從那時候起，他稱其爲“我被當成精神病的一段最詭異的人生經歷”開始了。

He was 12 or 13 when the psychiatrist prescribed antidepressants, which he dutifully took for two or three years. But they brought on terrible side effects: At one point he was hospitalized with suicidal thoughts.

在他十二三歲的時候，心理醫生一直給他處方抗抑鬱藥物，他聽話地堅持服用了兩三年。可這些藥物帶來了可怕的副作用：他一度因爲自殺念頭而不得不住院。

As a last resort, his parents took him from their home in Hillsville, Va., to see Dr. Yosipovitch, who was then at Wake Forest.

抱着最後一絲希望，他的父母帶他離開了位於弗吉尼亞州希爾斯維爾的家，來到維克森林大學拜訪當時在那裏工作的楊斯波維奇博士。

"He had a hunch on what it was," Mr. Riegel said.

“他好像憑直覺就知道是哪裏不對勁，”裏格爾先生說。

Tests found a rare form of a genetic disease, epidermolysis bullosa, that was causing a particularly destructive set of symptoms: intense itching and skin so fragile that scratching ripped it to shreds.

經過測試，研究人員發現他患有一種很罕見的遺傳病——大皰性表皮鬆解症(epidermolysis bullosa)，這種病可以造成一系列極具破壞性的症狀：劇烈瘙癢，皮膚極度脆弱，以至於連撓癢都會將皮膚劃破。

"Dr. Yosipovitch was quite angry I was being told I was mentally ill when I wasn't," Mr. Riegel recalled.

“在得知明明沒有精神病的我卻被人說成是精神病時，楊斯波維奇博士非常生氣，”裏格爾先生回憶道。

Getting off the antidepressants lifted his spirits and let him be normal again. Since then, other drugs have been prescribed for the itching, with mixed results. It never really goes away, but Mr. Riegel uses video games or his cellphone to take his mind off it and keep from scratching.

停用抗抑鬱藥物後，他的精神重新振奮起來，並恢復了正常。此後，醫生向他處方了其他藥物來治療瘙癢，效果好壞參半。雖然從未真正擺脫過瘙癢，但裏格爾先生可以藉助電腦遊戲或手機轉移自己的注意力，以避免抓傷自己。

For people with other types of chronic itching, Dr. Yosipovitch said: "This is just the beginning of a big era. In the next five years I predict there will be drugs targeted specifically for itch. We're in the middle of the tip of an iceberg."

對於患有其他類型慢性瘙癢的患者而言，楊斯波維奇博士說：“這個偉大的時代纔剛剛拉開序幕。預計在接下來的五年裏就會出現專門針對瘙癢的靶向藥物。我們正站在冰山的一角上。”