Brown recluse spiders (Loxosceles reclusa) are common in the U.S., mostly in the Midwest and South. The venom of the brown recluse spider can result in a necrotic lesion, which is usually the question asked on most standardized tests. However, it can rarely cause systemic loxoscelism, ranging from mild symptoms to death.
Over 50 species are present in North America. The “fiddleback” is commonly used to described L. reclusa but this finding is less reliable. Refer to the picture on this post to see the “fiddle” on the dorsal aspect. Ocular findings are more specific but difficult to recognize without magnification. There are many varieties of Loxosceles spiders in South America, notably Brazil. The brown recluse will usually avoid human contact, with most bites occurring when pressing a spider against the skin that was hiding in clothing or bedding.
The brown recluse’s venom contains sphingomyelinase D (activates complement, PMNs, and platelets), hyaluronidase, and several other destructive enzymes. These enzymes are responsible for the necrotic lesion that is seen. Before the necrotic lesion/eschar forms, the bite site usually appears similar to cellulitis. Erythema, induration and pain are frequently present soon after the bite. Systemic symptoms are rare but occur more frequently in children. Symptoms include malaise, myalgias, and nausea/vomiting. Loxosecelism can also include DIC, hemolytic anemia, rhabdomyolysis, renal failure, coma, and death.
Treatment is usually supportive in nature, although multiple therapies have been suggested and investigated, such as dapsone, colchicine, corticosteroids, hyperbaric oxygen, early surgical excision, and even antivenom. Dapsone theoretically works due to its anti-inflammatory properties rather than its antibiotic properties; however, many of the studies are in animal models and the results are varied. Currently dapsone is not recommended by most experts unless symptoms are severe. All of the other treatments have not shown great results in studies, although they are sometimes used depending on the clinical situation.
Equine antibody antivenom has been used since 1960s in Brazil and Fab fragment antivenom specific to the recluse has been developed in the U.S. in animal studies but hasn’t been studied clinically. In Brazil, antivenom is used only for systemic loxoscelism or severe cutaneous involvement.
Hogan C, Barbaro K, et al. Loxoscelism: Old Obstacles, New Directions. Ann Emerg Med. 2004; 44:608-624.
Andersen R, Campoli J, et al. Suspected Brown Recluse Envenomation: A Case Report and Review of Different Treatment Modalities. The Journal of Emergency Medicine. 2011; 41(2):e31-e37.
Vetter R, Swanson D. Bites of Recluse Spiders. Uptodate.com. Updated Dec. 12, 2011.