Brown Recluse Spider Envenomation 

Updated: Oct 14, 2021
Author: Thomas C Arnold, MD, FAAEM, FACMT; Chief Editor: Joe Alcock, MD, MS 

Overview

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. See the current distribution map below.

Complete distribution range of wild and domestic L Complete distribution range of wild and domestic Loxosceles reclusa (brown recluse spider). Courtesy of Wikimedia Commons (By ReliefUSA_map.gif: Public domain, U.S. government derivative work: Bob the Wikipedian).

Of the 13 species of Loxosceles in the United States, at least five have been associated with necrotic arachnidism. Loxosceles reclusa, or the brown recluse spider, is the spider most commonly responsible for this injury.

Typical appearance of a male brown recluse spider. Typical appearance of a male brown recluse spider. Photo contributed by Michael Cardwell, Victorville, Calif.
Spider envenomations, brown recluse. Close-up imag 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 cutan Dermonecrotic arachnidism represents a local cutaneous injury with tissue loss and necrosis.

See Arthropod Envenomation: From Benign Bites to Serious Stings and Venomous Spider Bites: Keys to Diagnosis and Treatment, Critical Images slideshows, for help identifying and treating various envenomations.

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. Laboratory studies have shown a decrease in hemolysis from brown recluse venom in the presence of complement inhibitors.[1] 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.

Etiology

Dermonecrotic arachnidism has been described in association with several species of Loxosceles spiders, but, in the United States, L reclusa venom is the most potent and the most commonly involved.

Epidemiology

US frequency

Although various species of Loxosceles are found throughout the world, L reclusa 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.[2, 3, 4] 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.[5]

The 2019 Annual Report of the American Association of Poison Control Centers recorded 790 individual exposures to brown recluse spiders, with 174 moderate outcomes, 24 major outcomes, and 0 dealths.[6]

Age

Systemic involvement, although uncommon, occurs more frequently in children than in adults.[7]

See the distribution map below.

Complete distribution range of wild and domestic L Complete distribution range of wild and domestic Loxosceles reclusa (brown recluse spider). Courtesy of Wikimedia Commons (By ReliefUSA_map.gif: Public domain, U.S. government derivative work: Bob the Wikipedian).

Prognosis

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.[8] Typical cases involve only local soft tissue destruction. The 2014 Annual Report of the American Association of Poison Control Centers recorded 275 minor outcomes, 218 moderate outcomes, 11 major outcomes, and no deaths.[6]

In South America, the more potent venom of the species Loxosceles laeta is responsible for several deaths each year.[9]

Patient Education

For patient education information, see the First Aid and Injuries Center as well as Black Widow Spider Bite and Brown Recluse Spider Bite.

 

Presentation

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 Examination

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 the image below).

Classic finding of a vesicle with surrounding eryt 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 (shown in the image below).

Spider bite, brown recluse. Within an hour, the bi 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.

Complications

Delayed skin grafting may be necessary after 4-6 weeks of standard therapy.

Losses of digits and amputations have been reported.

 

DDx

 

Workup

Laboratory Studies

Wound cultures and Gram stain may provide valuable information for local wounds.

If signs of systemic toxicity are present, monitor the patient for evidence of hemolysis, renal failure, and coagulopathy.

If treatment with dapsone is being considered, obtain a glucose-6-phosphate dehydrogenase (G-6-PD) level before treatment.

Other Tests

Several groups are currently developing laboratory methods of detecting brown recluse venom or venom components in tissue around the site of the bite.[10] One study suggests that exposure of red cells to brown recluse venom reduces their levels of glycophorin A; measurement of glycophorin A by flow cytometry may help identify exposed patients.[1] Once the technology to identify this venom in patients becomes readily available to the clinician, the ability to study this envenomation will burgeon.

Procedures

Conservative local debridement of necrotic lesions may be performed once the wound margins have been defined. Wide excision is disabling, disfiguring, and seldom indicated.

 

Treatment

Emergency Department Care

Treatment of brown recluse envenomation is directed by the severity of the injury. General wound management consists of local debridement, elevation, and loose immobilization of the affected area.

Because the activity of sphingomyelinase D is temperature dependent, application of local cool compresses is helpful and should be continued until progression of the necrotic process appears to have stopped.

Dapsone, because of its leukocyte inhibiting properties, frequently has been recommended by authorities to treat local lesions. However, because of the potential for adverse effects associated with dapsone use, especially in the setting of G-6-PD deficiency, appropriate caution should be exercised if using this medication.[11] To date, no well-controlled studies have shown dapsone to affect clinical outcome in human brown recluse envenomations; therefore, it is not routinely recommended.[12, 13]

Other treatments such as colchicine, steroids, antivenom, nitroglycerin patches, and surgical excision have been reported, but insufficient data exist to support their clinical use today.[14, 15]

Some evidence indicates that hyperbaric oxygen therapy is beneficial in an animal model for reducing skin lesion size, but controlled human studies of this technique have not been performed.[12, 16, 17]

Patients exhibiting signs of systemic toxicity should be admitted and evaluated for evidence of coagulopathy, hemolysis, hemoglobinuria, renal failure, or further progression of systemic illness.

Urinalysis can provide early evidence of systemic involvement (eg, hemoglobinuria, myoglobinuria) and can be performed easily at the bedside in all patients.

Inpatient care

Admit patients to the hospital for observation if they have rapidly expanding lesions or show evidence of systemic toxicity.

Patients with rapidly expanding lesions require good conservative wound care, including splinting and elevation. Appropriately treat any bacterial superinfection that occurs.

Carefully manage fluid and electrolytes in patients with evidence of systemic loxoscelism. Monitor patients' renal status and provide blood transfusions as needed. A short course of oral prednisone may reduce hemolysis. These patients may be discharged when their renal and hematologic statuses are stable.

Consultations

Consult a plastic surgeon or other specialist with experience in wound management in patients who might require delayed skin grafting or have a prolonged recovery period.

The images below show the progression of a brown recluse spider bite wound, which needed a skin graft for healing.

Spider bite, brown recluse. The third day after th Spider bite, brown recluse. The third day after the bite. The skin continues to die. Courtesy of Dale Losher.
Spider bite, brown recluse. Another view of the wo Spider bite, brown recluse. Another view of the wound 3 days after the bite. Courtesy of Dale Losher.
Spider bite, brown recluse. Nine days after the bi Spider bite, brown recluse. Nine days after the bite. The patient endured 8 days with an open wound to drain the spider's toxins and needed multiple doses of intravenous antibiotics and pain medication. Courtesy of Dale Losher.
Spider bite, brown recluse. Eleven days after the Spider bite, brown recluse. Eleven days after the bite. A 5-inch wide area of dead tissue was excised, necessitating skin grafting. Courtesy of Dale Losher.
Spider bite, brown recluse. Waiting to see skin gr Spider bite, brown recluse. Waiting to see skin graft results 38 days after the bite. Courtesy of Dale Losher.
Spider bite, brown recluse. Skin graft results 38 Spider bite, brown recluse. Skin graft results 38 days after the bite. Courtesy of Dale Losher.
Spider bite, brown recluse. View of healed wound a Spider bite, brown recluse. View of healed wound approximately 10 months after bite. Courtesy of Dale Losher.

Prevention

Persons living in endemic areas should wear protective clothing and remain attentive when venturing into habitats of the brown recluse spider.

Cobwebs and spiders should be carefully removed from under and behind beds. One should use caution when putting on clothing that has been kept in storage and not worn for some time.

Long-Term Monitoring

Before discharging patients from the hospital, instruct them on proper wound care techniques and in proper cooling of the lesion for the first 72 hours. Schedule patients for daily wound checks until the lesion is stable or improving.

At each follow-up visit for the first 72 hours, perform a urine bedside test for blood and a CBC count with platelet count to assess for any evidence of systemic toxicity.

Inform patients that the development of fever or dark urine necessitates immediate return to the ED or a call to their primary physician.

 

Medication

Medication Summary

Use tetanus prophylaxis, analgesics, and antipruritics as needed. Reserve antibiotics for evidence of true infection and do not administer prophylactically. Carlton recommends antihistamines and observation alone as treatment for brown recluse spider bites.[18]

No commercial antivenom for loxoscelism is currently approved for use in the United States. A horse-derived FAB antivenom is available in Argentina, Peru, Brazil, and Mexico, and it is indicated for cutaneous loxoscelism and cutaneous hemolytic manifestations.[9, 19] It is only a matter of time before a suitable antivenom may be available in the United States.

Antibiotics

Class Summary

Antibiotics should not be used prophylactically.  It has been suggested that antibiotics may minimize the local inflammatory component of cutaneous loxoscelism and decrease resulting skin necrosis.

Dapsone (Avlosulfon)

Dapsone is bactericidal and bacteriostatic against mycobacteria strains. The mechanism of action is similar to that of sulfonamides where competitive antagonists of p-aminobenzoic acids (PABA) prevent the formation of folic acid, causing bacterial growth inhibition.

If used, initiate the treatment with small doses followed by gradual increments. Monitor patients carefully because hypersensitivity, methemoglobinemia, and hemolysis in the presence of G-6-PD deficiency have been reported.

Corticosteroids

Class Summary

These agents have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli.

Use of corticosteroids is controversial in brown recluse spider bites. Evidence for using corticosteroids is insufficient.

Methylprednisolone (Solu-Medrol)

Methylprednisolone decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability.

Prednisone (Deltasone, Orasone, Meticorten)

Prednisone decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability.

Antihistamines

Class Summary

Antihistamines are used to treat minor allergic reactions and anaphylaxis. Diphenhydramine may be used to pretreat patients with prior documentation of minor allergic reactions. These agents may control itching by blocking effects of endogenously released histamine.

Diphenhydramine (Benadryl)

Diphenhydramine is used for symptomatic relief of allergic symptoms caused by histamine released in response to allergens.

 

Questions & Answers

Overview

What is the prevalence of brown recluse spider envenomation?

Which clinical syndromes result from brown recluse spider envenomation?

What is the pathophysiology of brown recluse spider envenomation?

What causes dermonecrotic arachnidism?

What is the frequency of brown recluse spider envenomation in the US?

In which age groups is brown recluse spider envenomation most frequent?

What is the prognosis of brown recluse spider envenomation?

Where can patient education resources for brown recluse spider envenomation be found?

Presentation

What are the signs and symptoms of brown recluse spider envenomation?

What are the symptoms of systemic loxoscelism due to brown recluse spider envenomation?

Which physical findings are characteristic of brown recluse spider envenomation?

What are potential complications of brown recluse spider envenomation?

DDX

What are the differential diagnoses for Brown Recluse Spider Envenomation?

Workup

What is the role of lab studies in the workup of brown recluse spider envenomation?

What is the role of flow cytometry in the workup of brown recluse spider envenomation?

What is the role of debridement in the management of brown recluse spider envenomation?

Treatment

What is included in emergency department (ED) care for brown recluse spider envenomation?

When is inpatient care indicated for brown recluse spider envenomation?

Which specialist consultations are helpful in the treatment of brown recluse spider envenomation?

How is brown recluse spider envenomation prevented?

What is included in long-term monitoring following treatment for brown recluse spider envenomation?

Medications

Which medications are used in the treatment of brown recluse spider envenomation?

Which medications in the drug class Antihistamines are used in the treatment of Brown Recluse Spider Envenomation?

Which medications in the drug class Corticosteroids are used in the treatment of Brown Recluse Spider Envenomation?

Which medications in the drug class Antibiotics are used in the treatment of Brown Recluse Spider Envenomation?