Scientists scratch heads over why we itch

Scientists scratch heads over why we itch
By Robert S. Boyd | McClatchy Newspapers
11/17/08

Scientists are baffled by one of humankind's most annoying problems " itching " an almost universal misery for which there is, as yet, no adequate explanation or treatment.

"Why we can't stop scratching remains a big puzzle for researchers,'' said Zhou-Feng Chen, a neuroscientist at Washington University, St. Louis.

"Itch can be devastating to patients and lead to extensive loss of quality of life,'' said Matthias Ringkamp, a researcher at Johns Hopkins University in Baltimore. "Unfortunately, the treatment of itch is often unsatisfactory.''

The recent discovery of an "itchy gene,'' however, may offer hope for better treatments, Chen said. A drug to block that gene might relieve the distress of itching.

Specialists on pruritus " the scientific term for itching " described their work Monday at the annual meeting of the Society for Neuroscience in Washington.

They distinguished between two major types of itch: a mild form that can be treated with common antihistamines such as Benadryl and a severe form that cannot.

"The second type is often severe and very common, since more than 50 diseases and conditions can cause it,'' said Glenn J. Giesler, a neuroscientist at the University of Minnesota in Minneapolis. "There are no treatments currently available for this latter type of itch. ''

As many as 10 percent of the people in the world endure chronic itching, said Ben Maddison, a researcher at Unilever, a multinational consumer-product corporation.

The itch-related gene identified by Chen is labeled GRPR, for gastrin-releasing peptide receptor. When he injected it under the skin of laboratory mice, they "scratched like crazy,'' he said.

"The discovery of the first itchy gene in the spinal cord raises the hope that it may be possible to relieve itchiness in patients by blocking the GRPR function,'' Chen said.

The discovery "puts us in a better position to design better drugs to help people suffering from a variety of disorders,'' said Ethan Lerner, a dermatologist at Massachusetts General Hospital in Boston.

Itching and pain are different but related, the neuroscientists said. The nerves that carry both sensations travel along closely spaced pathways through the spinal cord to the brain.

Robert LaMotte, an anesthesiologist at Yale University in New Haven, Conn., called these related pestilences ``itch and ouch.''

Mild itching often is caused by histamines, itch-inducing chemicals found in poison ivy, mosquito bites, pollens, etc. Antihistamines provide temporary relief from them.

Chronic itch may result from kidney, liver or blood disease, HIV, shingles, eczema or many other causes.

Scientists aren't sure why scratching helps relieve itching. ``We can only speculate,'' LaMotte said.

According to Giesler, scratching may prevent neurons on the spinal cord from responding to an itch-producing agent, thereby preventing the sensation from reaching the brain.

"Itch happens in your brain, not on your skin,'' said Clemens Forster, a researcher at the University of Erlangen in Germany.

ON THE WEB

More on pruritus and systemic disease
http://www.mcclatchydc.com/251/story/www.emedicine.com/derm/TOPIC946.HTM