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NOT RECLUSE—New mnemonic to prevent misdiagnosis of skin conditions as spider bites

Many dermatologic conditions are being mistaken for bites of the brown recluse spider, which leaves the patient’s real condition—potentially including life-threatening bacterial infections—under- or untreated. That’s according to a report from a group of researchers who have published a paper online in JAMA Dermatology (Feb. 15, 2017) that describes expressions of skin conditions that are often misdiagnosed as bites from this spider.

“People always tell you what a brown recluse bite looks like, so what I started emphasizing is, ‘This is what a brown recluse bite doesn’t look like,’” said author Rick Vetter, a retired University of California, Riverside entomologist and expert on the Brown Recluse, in a press release. “That message really has the potential to save lives.”

Vetter co-authored the paper with Dr. W. Van Stoecker and Dr. Jonathan Dyer, both dermatologists in Missouri who specialize in treating brown recluse bites.

In the paper, the authors note that infections caused by Staphylococcus aureus, Bacillus anthracis, Borrelia burgdorferi, Sporothrix schenckii, the herpes zoster virus, and even lymphoproliferative conditions such as lymphomatoid papulosis have been misdiagnosed as bites from the spider Loxosceles recluse, commonly known as the Brown Recluse. These false diagnoses occur all over North America, even in American states and Canadian provinces where no brown recluse populations are known to exist.

The authors provide a mnemonic device—NOT RECLUSE—which describes the most common skin signs that are not associated with brown recluse bite, but occur in mis-diagnosed lesions.

  • Numerous: More than one injury

  • Occurrence: The wound did not occur in a place where Brown Recluses are likely to be found. Either outside of the spider's geographic territory (see map below), or not in an enclosed space like a box, closet, or attic.

  • Timing: The wound arose sometime between November and March

  • Red Center: The center of the wound is red

  • Elevated: The middle of the wound is elevated, not sunken

  • Chronic: The wound has persisted for more than three months

  • Large: The injury is more than 10 centimeters wide

  • Ulcerates Too Early: The injury gets crusty within the first week

  • Swollen: The wound swells up if it's below the neck

  • Exudative: The wound is "wet," oozing pus or clear fluid

Past medical reports of Loxoscelism - a condition occasionally produced by the bite of the recluse spiders where the bite area becomes dusky and becomes a deep open sore as the skin around the bite dies - often did not adhere to the principles of evidence-based medicine, the authors note in their paper. Such erroneous reports artificially increased the list of signs associated with Loxocelism, which in turn decreased diagnostic accuracy.

“I‘m really on a crusade here,” Vetter said. “We have this knowledge that is counter to what many doctors and the general public are saying. And what they are saying is causing damage by misdiagnosis.”

Complete distribution range of wild and domestic Loxosceles reclusa. Photo courtesy of Bob the Wikipedian, distributed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

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