AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

The brown recluse spider (Loxosceles reclusa; see Media Files 1-2) is the most prevalent of the Loxosceles species in the United States. All Loxosceles species have the potential to inflict injury to varying degrees. Seen predominantly in the south central part of the United States, the brown recluse spider has been discovered as far north as Illinois and on both coasts. Other members of the Loxosceles species are found throughout the world.

Incidents involving the brown recluse spider usually occur in summer months as a consequence of the spider's activity patterns. Bites are rare, even in houses heavily infested with brown recluse spiders; therefore, a diagnosis of brown recluse spider bite is quite unlikely in areas that lack significant populations of Loxosceles spiders.

Bites of the recluse spider can cause a condition termed necrotic arachnidism, which begins with the development of an eschar at the bite site, followed by tissue necrosis and skin sloughing. Several groups of spiders have been linked to necrotic skin lesions, but recluse spiders cause most of these lesions. While most recluse bites heal uneventfully, some have a protracted course, with the wound taking months to resolve completely.

The recluse commonly is known as the fiddle-back or violin spider because of the distinguishing mark on its cephalothorax. The dull yellow-to-brown coloring of its body further distinguishes the brown recluse. It has a small body relative to its leg span, and 3 pairs of eyes rather than the 4 pairs typical of other spiders. The reclusive mannerism is demonstrated by the locations in which the spiders are encountered. They prefer dark, dry, and undisturbed locations, such as the undersides of logs, boards, and rocks and inside barns and garages. Genital bites have been seen on patients using outhouses. Within homes they are found in attics, closets, and storage areas for bedding, clothing, and furniture. Both the male and female spider can envenomate.

Pathophysiology

Bites and envenomation range from a mild, local, urticarial reaction to full-thickness necrosis.

The venom volume is minute, about 4 µL, with 65-100 mcg of protein. The venom contains alkaline phosphatase, 5'ribonucleotide phosphohydrolase, esterase, lipase, hyaluronidase, and, most importantly, sphingomyelinase D2. Sphingomyelinase D2 is responsible for calcium-dependent direct erythrocyte lysis. The degree of hemolysis is individually variable from 20% to more than 95%.

Cutaneous necrosis is completely dependent on activation of neutrophils. In rabbit studies, neutrophil infiltration occurs at 6 hours. Neutrophils significantly accumulate at 24-72 hours, preceding skin necrosis and ulceration. This explains why early dapsone initiation may be important to limit necrosis in bites destined for that reaction.

Frequency

United States

In 1994, 1835 brown recluse spider bites were reported to poison control centers nationwide.

International

The incidence of bites and envenomation is unknown.

Mortality/Morbidity

• Death is uncommon. Most patient occurrences documented with fatal envenomation have involved hematologic disorders in children.
• Systemic loxoscelism is unusual, especially in adults. Cutaneous loxoscelism is not uncommon with bites. Few envenomations, perhaps less than 10%, result in severe skin necrosis or other systemic manifestations.

Age

Systemic loxoscelism is most common in children.

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• Constitutional symptoms, including macular, papular, urticarial, petechial, scarlatiniform, or morbilliform eruption
• Hematologic disorders, such as hemolysis, hemoglobinuria, thrombocytopenia, disseminated intravascular coagulation, methemoglobinemia, and shock (rare but serious complications)
• Fever
• Headache
• Malaise
• Arthralgia and rhabdomyolysis
• Nausea
• Vomiting
• Renal failure

Physical

The bite typically is painless, and findings of a central papule and associated erythema may not be seen for 6-12 hours. Few envenomations, perhaps less than 10%, result in severe skin necrosis or other systemic manifestations.

• Wounds destined for necrosis usually show signs of progression within 48-72 hours of the bite.
• Central blistering with a surrounding gray-to-purple discoloration of the skin may be seen at the bite site.
• A surrounding ring of blanched skin is itself surrounded by a large area of asymmetric erythema leading to the typical "red, white, and blue" sign of a brown recluse bite. At this stage of evolution, these bites may be associated with significant pain related to incipient necrosis of skin and subcutaneous tissues. The resultant eschar and ulceration may take months to resolve.
• Note that patients who are destined for a severe reaction usually develop key signs within 6-12 hours, such as bullae formation, cyanosis, and hyperesthesia.
• Areas with increased adipose tissue, such as the thighs, buttocks, and abdomen, are more likely to undergo severe necrosis than bites occurring at other sites.

DIFFERENTIALS

Section 4 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Other Problems to be Considered

Necrotic skin lesions
Coumarin necrosis
Focal vasculitis
Venous and arterial ulcer
Necrotizing fasciitis
Factitious ulceration
Thromboembolic phenomenon
Trauma
Thromboangiitis obliterans
Diabetic neurocutaneous dystrophy
Tularemia
Mucormycosis
Anthrax

WORKUP

Section 5 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Lab Studies

• A CBC count may be pertinent to check for hematologic disorders, such as hemolysis, thrombocytopenia, and disseminated intravascular coagulation.
• Urine analysis for hemoglobinuria may prove valuable.
• Recently, a passive hemagglutination test was developed for diagnosis of brown recluse envenomation with good sensitivity and specificity that is capable of identifying envenomation up to 2 weeks after the incident. Unfortunately, the test is cumbersome to prepare, and results are not available for 6-24 hours, by which time initiation of a treatment regimen is indicated. Also discouraging use of the passive hemagglutination inhibition test are reports of false-negative results when the specimen contains exudate that is primarily bloody.
• Identification of captured spider by a qualified arachnologist is very helpful.

Procedures

• A skin biopsy may prove valuable.

Histologic Findings

Findings include eosinophils in association with fibrinoid necrosis of the dermal and subcutaneous arteriolar walls, a dense band of neutrophils, panniculitis, occlusive phlebitis, and vascular thrombosis. Large vessel vasculitis has been noted in a rabbit model of envenomation.

TREATMENT

Section 6 of 11  

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• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical Care

Treatments for the bite of the brown recluse have been varied and controversial.

• Almost all brown recluse spider bites heal nicely in 2-3 months without medical treatment. The long-term medical outcome is excellent without treatment. Avoid performing surgery.
• When treatment is deemed appropriate, make it conservative, using cold compresses, simple analgesics, elevation of an affected extremity, and cleansing of the bite site.
• • If tissue breakdown occurs and/or the bite appears in an anatomic site that is difficult to keep clean, add prophylactic antibiotics (eg, erythromycin, cephalosporin) to prevent the occurrence of a superimposed cellulitis; tetanus prophylaxis also is indicated.
  • Advise patients to avoid both strenuous exercise and local heat to help limit spread of the venom.
  • Dapsone has been shown to limit tissue destruction in some experimental models, but the results have been mixed and largely disappointing. A latency period of even a few hours before dapsone is started may negate any beneficial effects. Dapsone can cause hemolysis, especially in the setting of G-6-PD deficiency.

  • Intralesional steroids may do more harm than good and have not been of benefit.

  • Systemic steroids may be involved in systemic loxoscelism by preventing red blood cell hemolysis.

  • Antivenom is not commercially available for L reclusa. The only commercially available antivenom is for Loxosceles laeta in South America.

• In short, in most patients, no systemic agent currently can be recommended to prevent necrosis. Prescribe systemic steroids only for patients with systemic loxoscelism.

Surgical Care

Necrotic skin lesions occur in 10% of patients with envenomization. Excision of a necrotic skin site may be advisable (especially for the rare large lesion) but only after 6-8 weeks of wound care, by which time an eschar has formed, adjacent tissues seem to have recovered, and normal healing is possible. Early surgery usually is inadvisable in the care of cutaneous loxoscelism.

The practice of incising/lacerating the area of the bite to drain the venom is also not advised in light of the minute amount of venom injected. The surgery also increases the amount of local inflammation and potentiates the venom's effects. This surgical practice usually increases morbidity and is detrimental to the healing process in light of incurring an open wound than requires much more wound care than does the closed necrotic eschar.

Activity

Advise patients to avoid both strenuous exercise and local heat to help limit spread of the venom.

MEDICATION

Section 7 of 11  

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• Workup
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• Miscellaneous
• Multimedia
• References

Antibiotics and tetanus prophylaxis are indicated. Early trials with humans indicate that intralesional steroids may do more harm than good and have not been of benefit. Systemic steroids may be involved in systemic loxoscelism by preventing red blood cell hemolysis. Antivenom is not commercially available for L reclusa.

Drug Category: Antibiotics

Dapsone has been shown to limit tissue destruction in some animal models. It is prescribed in some patients, although recent research suggests it is of little value after necrosis becomes evident and may be of little value when administered after even a brief delay. Although no systemic agent currently can be recommended to prevent necrosis in most bites, more research is necessary. Before prescribing dapsone, become thoroughly familiar with the risks associated with the drug. Erythromycin or a cephalosporin may be useful to prevent superimposed cellulitis.

Drug Name	Cefazolin (Ancef, Kefzol, Zolicef)
Description	First-generation semisynthetic cephalosporin that arrests bacterial cell wall synthesis, inhibiting bacterial growth. Primarily active against skin flora, including Staphylococcus aureus. Typically used alone for skin and skin-structure coverage. IV and IM dosing regimens are similar.
Adult Dose	250 mg to 2 g IV/IM as soon as possible
Pediatric Dose	25-100 mg/kg/d IV/IM as soon as possible
Contraindications	Documented hypersensitivity
Interactions	Probenecid prolongs effect of cefazolin; coadministration with aminoglycosides may increase renal toxicity; may yield false-positive urine-dip test for glucose
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Adjust dose in renal impairment; superinfections and promotion of nonsusceptible organisms may occur with prolonged use or repeated therapy

Drug Category: Biologic and immunologic agents

Tetanus immune globulin is used for passive immunization against tetanus. Tetanus toxoid is used to induce active immunity against tetanus in selected patients.

Drug Name	Tetanus toxoid
Description	The immunizing agents of choice for most adults and children > 7 y are tetanus and diphtheria toxoids. Necessary to administer booster doses to maintain tetanus immunity throughout life. Pregnant patients should receive only tetanus toxoid, not a diphtheria antigen-containing product. In children and adults, may administer into deltoid or mid lateral thigh muscles. In infants, preferred site of administration is mid thigh laterally.
Adult Dose	Primary immunization: 0.5 mL IM, give 2 injections 4-8 wk apart and a third dose 6-12 mo after second injection Booster dose: 0.5 mL q10y
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity; history of neurologic symptoms or signs following administration of this product; FDA recommends that elective tetanus immunization be deferred during outbreaks of poliomyelitis because tetanus toxoid injections are important cause of provocative poliomyelitis
Interactions	Patients receiving immunosuppressants, including corticosteroids or radiation therapy, may remain susceptible despite immunization because of poor immune response; cimetidine may enhance or augment delayed-hypersensitivity responses to skin test antigens; avoid concurrent use of medication with systemic chloramphenicol since it may impair amnestic response to tetanus toxoid; concurrent use of tetanus immune globulin may delay development of active immunity by several days (interaction is nevertheless clinically insignificant and does not preclude its concurrent use)
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Do not use to treat actual tetanus infections or for immediate prophylaxis of unimmunized individuals (instead, use tetanus antitoxin, preferably human tetanus immune globulin); diminished antibody response to active immunization may be seen in patients receiving immunosuppressive therapy; better to defer primary diphtheria immunization until immunosuppressive therapy discontinued; routine immunization of symptomatic and asymptomatic persons with HIV infection is recommended

Drug Category: Hyperbaric oxygen

To decrease healing time or persistent ulceration.

FOLLOW-UP

Section 8 of 11  

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• Introduction
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• Follow-up
• Miscellaneous
• Multimedia
• References

Further Inpatient Care

• Inpatient care is not indicated for cutaneous loxoscelism.
• In systemic loxoscelism, a hemolytic episode is seen that usually is self-limited and requires no special treatment. Systemic steroids with intravenous hydration and monitoring of renal function may be needed in some cases.

Further Outpatient Care

• Monitor patients weekly. Instruct patients to return sooner if signs of infection or jaundice occur.

Deterrence/Prevention

• Pesticides are ineffective against spiders and, therefore, do not prevent bites.

Prognosis

• Prognosis for this condition is good, and most patients show an excellent outcome.
• Within approximately 1 week, pain subsides, and usually, a striking reduction in the size of the necrosis is seen.
• Healing may be slow, but all lesions heal. Most often, a minimum of scarring is seen.

Patient Education

• Instruct patients to become familiar with their environment and to learn how to recognize the brown recluse spider (see Media Files 1-2). Patient awareness is the primary factor in making the correct diagnosis and forming the appropriate treatment path for the bite of the brown recluse.
• For excellent patient education resources, visit eMedicine's Bites and Stings Center and Infections Center. Also, see eMedicine's patient education articles Brown Recluse Spider Bite, Black Widow Spider Bite, and Tetanus.

MISCELLANEOUS

Section 9 of 11  

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• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

• Failure to use caution and monitor patients on dapsone. Order baseline G-6-PD test and CBC count with follow-up CBC count at regular intervals.
• Failure to use caution in patients with methemoglobin reductase deficiency or hemoglobin M because of the high risk for hemolysis and Heinz body formation
• Failure to use caution in patients exposed to other agents or conditions (eg, infection, diabetic ketosis) capable of producing hemolysis. Peripheral neuropathy can occur, although rarely. Phototoxicity may occur when exposed to UV light.

MULTIMEDIA

Section 10 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Brown recluse spider. Courtesy of US Centers for Disease Control and Prevention.
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Media file 2:  Brown recluse spider. Courtesy of US Centers for Disease Control and Prevention.
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Media file 3:  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.
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Media file 4:  The third day after the bite. The skin continues to die. Courtesy of Dale Losher.
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Media file 5:  Another view of the wound 3 days after the bite. Courtesy of Dale Losher.
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Media file 6:  Nine days after the bite. The patient endured 8 days with an open wound to drain the spider's toxins and needed intravenous antibiotics and pain medication almost 24 h/d. Courtesy of Dale Losher.
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Media file 7:  Eleven days after the bite. A 5-inch wide area of dead tissue was excised, necessitating skin grafting. Courtesy of Dale Losher.
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Media file 8:  Brown recluse spider bite. Waiting to see skin graft results 38 days after the bite. Courtesy of Dale Losher.
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Media file 9:  Skin graft results 38 days after the bite. Courtesy of Dale Losher.
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Media file 10:  View of healed wound approximately 10 months after bite. Courtesy of Dale Losher.
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Media file 11:  This is a typical brown recluse bite 1 week after medical therapy with early use of dapsone (within 72 h).
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Media file 12:  This is the same lesion (as in Image 11) only on dapsone and topical antibiotic 1 month later. One can see good delineation of margins and granulation tissue at edges and base. This eschar was debrided at this point and has healed well with topical antibiotics and daily dressing changes.
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REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

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Article Last Updated: Jan 27, 2006