Mechanisms Behind Chronic Itching Identified in New Study

The mechanisms driving chronic itching differ from the transient urge to scratch a bug bite, experiments in mice reveal.

According to a study published in The Journal of Clinical Investigation, chronic itching seems to involve more than just those neurons usually responsible for transmitting itch signals, going so far as to co-opt pain neurons to intensify the sensation.

"In normal itching, there's a fixed pathway that transmits the itch signal," senior investigator Zhou-Feng Chen, director Washington University's Center for the Study of Itch, said in a statement. "But with chronic itching, many neurons can be turned into itch neurons, including those that typically transmit pain signals. That helps explain why chronic itching can be so excruciating."

Chen and his colleagues generated mice in which the gene BRAF is constantly active, sending signals inside itch neurons. While researchers know that BRAF and the protein it generates are involved in the body's response to pain, it was not clear whether or not the gene is a part of itching -- until now.

"We thought the animals might be prone to feeling pain rather than itching," Chen said. "To our great surprise, the mice scratched spontaneously. At first, we didn't know why they were scratching, but it turns out we developed a mouse model of chronic itch."

Research revealed that the BRAF protein could switch on a myriad of itch genes. The team also discovered similar changes of gene expression in mice with chronic itching due to dry skin as well as those with allergic contact dermatitis, both of which cause itching in humans.

Based on these findings, the scientists hypothesize that by targeting proteins in the BRAF pathway, new treatments for chronic itching may be developed. One possible form of therapy, the researchers argue, is pain medication.

"Certain drugs are used to inhibit some of the same targets in patients with chronic pain, and those medications also may quiet down itch," Chen said, adding that "There are many pathways leading from BRAF, and all of these could be potential targets for anti-itch therapies."