How should we define itching?,☆☆

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Abstract

The standard definition of itching (as “an unpleasant sensation that provokes the desire to scratch”) takes no account of recent advances in knowledge about itch physiology. Always imprecise, this definition is also out-of-date. Its defects are discussed in this article, and some modifications are proposed. (J Am Acad Dermatol 1998;38:268-9.)

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EXCLUSIONS

His definition obviously excludes those who enjoy a regular workout on their scratch/itch cycles, for whom “‘tis better than riches to scratch where it itches.”3 In his classic essay, Ayres4 reminds us that Socrates often referred to mixed sensations of pleasure and pain. As Michel de Montaigne said in the sixteenth century, “Scratching is one of nature’s sweetest gratifications, and the one nearest to hand.” The definition has other problems as well. Common sense tells us that animals itch,

POSITRON EMISSION TOMOGRAPHY

At one stage, I had hoped for help from an important recent article entitled, “Urge to Scratch Represented in the Human Cerebral Cortex During Itch.”9 Its authors looked into the central processing of itch in persons who had been given injections of histamine into the skin of the right arm, but who were not allowed to scratch. Certain areas of their brains lit up when assessed by positron emission tomography, a measure of regional cerebral blood flow. These areas included the inferior parietal

A NEW DEFINITION

These findings, I had hoped, might form the basis for a new definition of itching. I began to think along the lines of: “Itching is that sensation which is accompanied by the contralateral activation of the anterior cingulate cortex, and the predominantly ipsilateral activation of the supplementary motor areas, the premotor areas, and the inferior parietal lobule. Scratching may follow.” This definition covers both animals and humans, does not rule out those who enjoy scratching and side-steps

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Reprint requests: John Andrew Savin, MD, Consultant Dermatologist, The Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh EH3 9YW, Scotland.

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