Appearing and Disappearing Scratch Marks

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A 41-year-old man complains of “red lines” that appear on his skin soon after minor scratching trauma. They manifest rapidly but disappear within minutes (occasionally as long as an hour), leaving no trace. They cause no symptoms but are nonetheless disturbing to the patient.

In terms of his overall health, the patient has few problems beyond mild seasonal allergies. However, he reports experiencing a great deal of stress recently. He denies taking any prescription medications regularly, though in the spring, he often takes OTC antihistamines to ward off sneezing and itchy eyes.

A linear wheal appears after the skin is scratched with the dull edge of a fingernail. The initial reaction to the scratch is a macular red flare, followed within seconds by a broadening band of erythema. Seconds later, the frank wheal appears. The lesion is warmer than the surrounding skin but not at all tender. As expected, it clears completely within a few minutes, leaving no sign of its ever having been there.

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