Scratching the surface of an itchy question

Washington -- What exactly causes an itch? It's an everyday quandary of medicine. But finding a resolution -- and an effective treatment -- can leave doctors scratching their heads.

The usual suspects are always in the lineup: chickenpox, psoriasis, dry skin, insect bites, poison ivy and any number of allergies. But there's also the chance that the itch might be more than skin deep, a sign of obstructive liver disease, renal failure, hyperthyroidism, Hodgkin's disease or other lymphomas, or HIV.

The age-old problem is now receiving increased attention as new emphasis is being placed on classifying the itch's cause as a means to take advantage of more specific treatments.

Even with this development, challenges for physicians are significant.

"Itch is a very difficult symptom to understand and define," said Jeffrey D. Bernhard, MD, professor of medicine at the University of Massachusetts Medical Center in Worchester. He was part of a panel of experts addressing a February meeting of the American Academy of Dermatologists in Washington, D.C.

And defining it is only the beginning. "We know that sometimes itching patients are not easy patients," said Dr. Torello Lotti, professor of dermatology at the University of Florence in Italy. "There are some kinds of itch that are almost impossible to understand and treat."

In an effort to address this, a team of researchers recently developed a four-part system to differentiate among an itch's origins. For difficult cases, classifying the type of itch can be helpful, said Dr. Malcolm Greaves, emeritus professor of dermatology at the University of London. "You have to start somewhere."

The newly devised categories include itches generated in the skin, those arising in the peripheral nervous system and those emanating from the central nervous system. A fourth category, psychogenic, includes those that spring from a psychological condition. Not all patients fit neatly into a single grouping, which has caused controversy and triggered some doctors to question the framework's usefulness. Still, pinpointing how an itch originates can help in deciding whether ointment or psychotherapy should be the first-line treatment.

Physicians also must try to rule out the possibility that an underlying disease is acting as a trigger, Dr. Greaves said, and keep in mind that opioid therapy can cause itching.

Physicians might think that if they can't find an organic reason for a patient's itch despite a "million-dollar workup," the cause must be psychological, said John Koo, MD, clinical professor of dermatology at the University of California San Francisco. That's not necessarily true, he said.

But pruritus can be made worse by such disorders as depression or anxiety. Also, some patients seem to want to punish themselves by scratching. There are even a few who enjoy having an itch, he said. "Those people can get almost an erotic reaction from scratching."

For patients who have skin disease and an emotional overlay, physicians have to treat the condition on all levels, Dr. Koo said. "You may have three things to cope with. It's like a door with three locks. You need to use three keys simultaneously."

What works

When Dr. Greaves is presented with a patient who has a seemingly impossible itch, he first turns to broadband UVB phototherapy, prescribing it three times a week for 12 weeks. Although he said it is probably the most effective single therapy, how it works remains a mystery.

Dr. Greaves also considers prescribing the tricyclic antidepressant doxepine, beginning with a low initial dose and building slowly; or he tries opioid antagonists or the selective serotonin reuptake inhibitor paroxetine.

Dr. Jana Hercogova, a professor of dermatology at Charles University in Prague, described several topical anti-itch treatments, including some old standards such as calamine lotion and cool compresses, as well as a few investigational drugs.

Local preparations can work in one of three ways, she said. They can substitute another sensation -- cool, hot or a counter-irritant; they can anesthetize the sensory nerve endings; or they can run opposition to powerful itch-inducing neuropeptides.

For reducing skin inflammation, there is an army of topical dermatology drugs, including corticosteroids, Dr. Hercogova said, although she cautioned that steroids shouldn't be a first-line therapy until the underlying disorder has been identified.