Why chronic itching can be so excruciating

Washington: For those who have suffered through sleepless nights due to uncontrollable itching know that not all itching is the same.

A new research at Washington University School of Medicine in St. Louis explains why.

Working in mice, the scientists have shown that chronic itching, which can occur in many medical conditions, from eczema and psoriasis to kidney failure and liver disease, is different from the fleeting urge to scratch a mosquito bite.

That's because chronic itching appears to incorporate more than just the nerve cells, or neurons, that normally transmit itch signals.

The researchers found that in chronic itching, neurons that send itch signals also co-opt pain neurons to intensify the itch sensation.

The new discovery may lead to more effective treatments for chronic itching that target activity in neurons involved in both pain and itch.

"In normal itching, there's a fixed pathway that transmits the itch signal," senior investigator Zhou-Feng Chen, PhD, who directs Washington University's Center for the Study of Itch, said.

"But with chronic itching, many neurons can be turned into itch neurons, including those that typically transmit pain signals. That helps explain why chronic itch ing can be so excruciating," he said.

The research is published online in The Journal of Clinical Investigation.

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