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Spider Envenomation, Brown Recluse
Updated: Aug 18, 2009
Introduction
Background
In the United States, reports of severe envenomations by brown spiders began to appear in the late 1800s, and today, in endemic areas, brown spiders continue to be of significant clinical concern.
Of the 13 species of Loxosceles in the United States, at least 5 have been associated with necrotic arachnidism. Loxosceles reclusus, or the brown recluse spider, is the spider most commonly responsible for this injury.
Typical appearance of a male brown recluse spider. Photo contributed by Michael Cardwell, Victorville, Calif.
Spider envenomations, brown recluse. Close-up image of dorsal violin-shaped pattern. Photo contributed by Michael Cardwell, Victorville, Calif.
Dermonecrotic arachnidism refers to the local skin and tissue injury noted with this envenomation. Loxoscelism is the term used to describe the systemic clinical syndrome caused by envenomation from the brown spiders.
Dermonecrotic arachnidism represents a local cutaneous injury with tissue loss and necrosis.
Pathophysiology
Brown recluse spider bites can cause significant cutaneous injury with tissue loss and necrosis. Less frequently, more severe reactions develop, including systemic hemolysis, coagulopathy, renal failure, and, rarely, death.
Brown recluse venom, like many of the other brown spider venoms, is cytotoxic and hemolytic. It contains at least 8 components, including enzymes such as hyaluronidase, deoxyribonuclease, ribonuclease, alkaline phosphatase, and lipase. Sphingomyelinase D is thought to be the protein component responsible for most of the tissue destruction and hemolysis caused by brown recluse spider envenomation. The intense inflammatory response mediated by arachidonic acid, prostaglandins, and chemotactic infiltration of neutrophils is amplified further by an intrinsic vascular cascade involving the mediator C-reactive protein and complement activation. These and other factors contribute to the local and systemic reactions of necrotic arachnidism.
Although numerous cases of cutaneous and viscerocutaneous reactions have been attributed to spiders of the genus Loxosceles, confirming the identity of the envenomating arachnid is difficult and rarely accomplished.
Frequency
United States
Although various species of Loxosceles are found throughout the world, L reclusus is found in the United States from the East to the West Coast, with predominance in the south. Recently, reports of persons with "spider bites" presenting to emergency departments have reached near urban legend proportions, prompting many physicians to question the diagnosis of a brown recluse bite in nonendemic areas. The list of conditions that can present in a similar fashion to that of a brown recluse spider envenomation is extensive. A more likely explanation for this epidemic of spider bites is in fact community-acquired methicillin-resistant Staphylococcus aureus (MRSA) skin infections.1
Mortality/Morbidity
- Data regarding mortality rates are not reliable because diagnostic tests to detect brown recluse venom in tissue are not readily available.
- Although deaths have been attributed to presumed brown recluse envenomation, severe outcomes are rare. Typical cases involve only local soft tissue destruction.
- In South America, the more potent venom of the species Loxosceles laeta is responsible for several deaths each year.
Age
Systemic involvement, although uncommon, occurs more frequently in children than in adults.
Clinical
History
- The brown recluse spider, living up to its name, is naturally nonaggressive toward humans and prefers to live in undisturbed attics, woodpiles, and storage sheds.
- Brown recluse spiders vary in size and can be up to 2-3 cm in total length. They are most active at night from spring to fall.
- Characteristic violin-shaped markings on their backs have led brown recluse spiders to also be known as fiddleback spiders.
- Envenomation from the brown recluse spider elicits minimal initial sensation and frequently goes unnoticed until several hours later when the pain intensifies.
- An initial stinging sensation is replaced over 6-8 hours by severe pain and pruritus as local vasospasm causes the tissue to become ischemic.
- Symptoms of systemic loxoscelism are not related to the extent of local tissue reaction and include the following:
- Morbilliform rash
- Fever
- Chills
- Nausea
- Vomiting
- Joint pain
- Hemolysis
- Disseminated intravascular coagulation (DIC)
- Renal failure
- Seizures
- Coma
Physical
- Edema around the ischemic bite site produces the appearance of an erythematous halo around the lesion.
- The erythematous margin around the site continues to enlarge peripherally, secondary to gravitational spread of the venom into the tissues.
- Typically, at 24-72 hours, a single clear or hemorrhagic vesicle develops at the site, which later forms a dark eschar (see Media file 1).
Classic finding of a vesicle with surrounding erythema at 24 hours following brown recluse envenomation. Photo by Thomas Arnold, MD.
- Necrosis is more significant in the fatty areas of the buttocks, thighs, and abdominal wall.
Spider bite, brown recluse. Within an hour, the bite area swelled to the size of a quarter. The area turned blue and dark red by the evening of the first day, exceeding the boundaries of a circle drawn around the area of initial swelling by the patient's physician. Courtesy of Dale Losher.
Causes
Dermonecrotic arachnidism has been described in association with several species of Loxosceles spiders, but, in the United States, L reclusus venom is the most potent and the most commonly involved.
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References
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Further Reading
Keywords
Loxosceles reclusus, brown recluse spider, fiddleback spider loxoscelism, necrotic arachnidism, dermonecrotic arachnidism, spider bite, brown recluse bite, envenomations, Loxosceles laeta, morbilliform rash, disseminated intravascular coagulation, DIC, renal failure, seizures, coma, eschar, spider envenomation
