Brown recluse spiders(Loxosceles reclusa) are known to cause necrotic skin reactions with their bite and often are blamed for cases of skin necrosis even in areas they do not inhabit. This can lead to misdiagnosis and delay in appropriate treatment for other conditions. Swanson and Vetter reviewed the available literature on the epidemiology, evaluation, and treatment of these bites.
Brown recluse spiders are found in several areas of the United States, including southeastern Nebraska, Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Kentucky, Tennessee, Mississippi, Alabama, northern Georgia, and southern portions of Ohio, Indiana, Illinois, and Iowa. They are not endemic in the west, northeast, midatlantic, or coastal south. Other Loxosceles spiders exist in the southwest, although most ulcerating spider bites are caused by the brown recluse. Bites have been noted outside endemic areas, but these reports are questionable.
Reported spider bites often are caused by other arthropods (e.g., ticks, fleas), and only about one in 10 patients with a suspected spider bite submits a spider specimen. Furthermore, bites are uncommon even in homes with known infestation. Definitive diagnosis is made by confirmation of a bite and positive identification of the spider by an arachnologist; there are no laboratory tests available for clinical use. Ulcerating wounds have many possible causes, including infection, vascular disorders, neoplasm, and trauma. This extensive differential diagnosis, combined with the relative rarity of brown recluse bites and the difficulty of confirming a bite, should make physicians cautious in diagnosing a brown recluse envenomation.
There are many proposed treatments for brown recluse bites, although in most cases the bites will heal without therapy. No randomized controlled trials have been performed. The sulfone antibiotic dapsone often is recommended, although no prospective trials support its use for bites in humans. Other treatments include steroids, surgical excision, hyperbaric oxygen, local electrical shock, and antivenom (not available in the United States); none has been proven effective for brown recluse bites. Because bites most often are self-limited, typical wound care is the best option in unconfirmed cases.