Let it itch, Pruritus

15. November 2010
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Every fifth person develops a chronic pruritus during his or her life. But this irrepressible urge to scratch was not taken serious for a long time. Today new drugs and therapies bring hope to millions of people suffering from pruritus.

Scraped off skin, bloody spots all over the body and the permanent urge to scratch: About 17 percent of the working population suffers from pruritus, for about four percent that problem is severe or chronic. But although this illness strains body and soul enormously, only six percent of the people are seeing a physician for treatment. For many years, the burning, pricking and scratching was considered an attendant symptom of a handful of skin diseases. Dermatologists had only few treatment options, thus the prospect of an effective therapy was rather humble. But the picture starts changing – especially here in Germany which is the first country worldwide opening ‘itch-outpatient departments’ and which has developed a treatment guideline for physicians.

Not every itch is just another itch: Allergic reactions, bacteria- or mycotic infections, skin cancer, viruses, lice, dry skin, liver- or kidney disorders – all those might lead to a pruritus, just like certain drugs or cosmetic agents. Amines, prostaglandins and neuropeptides are some of the mediators causing pruritus. One of the most important mediators for an itching reaction is histamine. “If you inject this messenger under the skin, it starts itching right away”, says Clemens Forster at the Institute for Physiology and Pathophysiology of the University of Erlangen-Nurnberg. He examines the itching scientifically. The body stores its histamine supply in the mastocytes. They pour them out within seconds for example after a sting by a mosquito. In 1997, scientists found the according nerve fibers. “They end freely in the skin. Once they get in touch with histamine, they immediately send an itch-signal to the spinal cord. There the message is redirected to other nerve fibers and forwarded to the brain”, explains Forster. In most of the cases, this is followed by an irresistible urge to scratch.

And indeed – the rubbing and scratching brings relief – even if you hurt yourself and in the word’s meaning scratch off the skin of your body. An American patient supposedly succeeded in scratching through her skullcap all the way through to her brain. While scratching with the fingers, the pain signal overlaps the pruritus. Moreover, the activities in those parts of the brain decrease which create unpleasant feelings and memories. But the effect is short-term. And a wound is added which needs to heal and in doing so itches as well. A vicious circle of itch-scratch develops.

If the feeling lasts for more than six weeks in a row, the pruritus became chronic. In order to avoid that, therapy has to be started as early as possible. “When it’s itching, the following rule applies: Nip it in the bud”, explains Prof. Sonja Ständer. The expert is head of the first itch-outpatient department at the dermatological hospital in Münster/Germany. Day after day she treats arms with vesicular lesions, scratched open legs and maltreated bodies of people suffering from a permanent pruritus. And successful: “We are able to help 70 percent of our patients if we treat them according to the guidelines”, says Ständer.

In the fight against the itching, taking care of the maltreated skin ranks first. “Cooling lotions and itch-relieving creams improve the disturbed balance of the skin and rebuilds its barrier function”, Ständer explains. With that you can lengthen the phases without any signs of the disease and curb the frequency and severity of inflammations. Depending on the cause, also ointments containing capsaicin relieve the pruritus. Antihistamines inhibit the binding of histamine and immunosuppressive agents like glucocorticoids hold the immune system during bad phases. “Tacrolismus, pimecrolismus seem to affect additionally on the nerve fibers“, says Prof. Ständer. The itching might increase also if pain-transmitting nerves are blocked by opioids. Then opioid-antagonists like naltrexone often help against the itching.

But by far not every patient can be helped with these drugs, because as manifold the causes, as individual has to be the therapy. For example the person suffering from neurodermatitis needs a different treatment than a cancer patient with pruritus or a patient with a mycotic infection. Especially pruritus presents dermatologists with a challenge. But since the scientific interest in the genesis of pruritus has started growing, scientists discover more and more active agents possibly helpful for pruritus patients. “But often they are not even really new”, states Prof. Sonja Ständer. Gabapentin for example is normally use for epilepsy patients and for pain therapy. For itch patients the remedy is supposed to stop the itchiness being transmitted to the brain. Also serotonin-reuptake inhibitors of the group of antidepressants belong to those ‘off-label-use’ drugs. “Over the past years we have made very good experience with these substances”, says Ständer. Another drug might enlarge the range very soon. The kappa-opioid-antagonist nalfurafin supplies convincing results in studies with hemodialysis-patients suffering from a strong itching sensation. The drug is already approved in Japan.

Ständer and her colleagues now have tested another therapy option. An important mediator during the development of itchiness is the neuropeptide substance P. In a study, they gave patients suffering from chronic pruritus a counterpart: Aprepitant. In 80 percent of the test persons, the symptoms improved significantly, the largest effect was with people with skin diseases. “Most of all new therapies applied lately for pruritus patients, aprepitant turned out to be the most effective”, states Prof. Ständer.

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1 comment:

Gisela Cartmill
Gisela Cartmill

Very little is published on idiopathic “itsching”, that has been really helpful to me . This is very interesting, especially the fact, that there is some research for medication going on right now and that it seems to be much more common that I knew. I will follow the progress of the new meds.

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