Insect bites and stings are a relatively common occurrence with more than 50,000 exposures occurring per year in the United States.1 Slightly less than half of these injuries are spider bites. One of the most clinically significant spiders is the recluse spider, whose bite can progress to ulcerating dermonecrosis at the bite site.
Brown recluse spiders are part of the genus Loxosceles. They inhabit several areas of the United States including Colorado, southeast Nebraska, Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Kentucky, Tennessee, Mississippi, Alabama, northern Georgia, southern Ohio, southern Indiana and southern Illinois.2 Studies have reported brown recluse spider bites in California and other western states, but authors believe these to be a misdiagnosis as the brown recluse spider has not established itself outside of its native range.3 Both the hobo spider and the yellow sac spider can cause similar necrotic bites, but these are usually less severe than a recluse spider bite.4
Recluse spiders are rarely aggressive and bites are uncommon. Most bites occur when the spider gets pressed against the skin by clothing, towels, bedding or gloves. Bites most frequently occur at night and in the early morning during warmer months. Frequently, patients do not feel the recluse bite and it does not cause immediate pain.
Brown recluse spiders have several toxins, the most clinically significant being the hemotoxic agent sphingomyelinase D.5 Direct cytotoxicity from this venom component, as well as autoimmune response from cytokines and lymphocytes, theoretically result in the necrosis and systemic symptoms that can arise from recluse spider bites.6 Most recluse spider bites are minor and spontaneously resolve without necrosis. Recluse spider bites can result in the clinical condition of loxoscelism, which is the only proven type of necrotic arachnidism in humans.6 There are two forms of loxoscelism: necrotic cutaneous loxoscelism and viscerocutaneous loxoscelism. A small number of bites produce dermonecrotic skin lesions and an even smaller number of bites produce systemic symptoms. A study by Leach and colleagues found that skin necrosis occurred in 37 percent of recluse spider bites and systemic illness occurred in 14 percent of cases.7
In necrotic cutaneous loxoscelism, symptoms secondary to the recluse spider bite remain localized to the skin. Dermonecrotic skin lesions typically begin with pain and burning at the bite site that progress for two to eight hours after the initial bite occurred. Over the next 12 to 36 hours, symptoms progress with the bite area first becoming pale and the surrounding area becoming red and edematous. The area then develops a bluish, hard, stellate center that becomes progressively more necrotic and eventually sloughs.5,8 The amount of dermal necrosis can be quite extensive with ulcerative necrotic areas up to 40 cm reported.5
In approximately 14 percent of cases, recluse bites result in a combination of local cutaneous and systemic symptoms known as viscerocutaneous loxoscelism.7 Common systemic symptoms include low energy, nausea, vomiting and fever. In advanced cases, the recluse spider hemotoxin can cause destruction of red blood cells, resulting in hemolytic anemia.2 Myonecrosis and rhabdomyolysis from loxoscelism can lead to renal failure.9 Severe bleeding can occur due to destruction of platelets resulting in thrombocytopenia and consumption of clotting factors leading to disseminated intravascular coagulation.2
There are numerous infectious and non-infectious conditions that can produce necrotic wounds similar to the recluse spider bite and physicians misdiagnose an estimated 80 percent of recluse spider bites.5 As I stated previously, the hobo spider and yellow sac spider can cause necrotic bites that are usually less severe than a recluse spider bite.4 Other conditions with symptoms similar to recluse spider bites include: pyoderma gangrenosum, staphylococcal or streptococcal infection, herpes zoster or herpes simplex, diabetic ulcers, fungal infection, chemical burn, Toxicodendron dermatitis, squamous cell carcinoma, vasculitis, syphilis, toxic epidermal necrolysis, erythema multiforme, purpura fulminans, sporotrichosis and Lyme disease.2,10 One of the most common and clinically significant differential diagnoses for recluse spider bites is nosocomial or community-acquired methicillin-resistant Staphylococcus aureus infection.11
A Closer Look At Treatment Options
Despite being one of the most clinically significant spider bites, recluse spider bites have no established treatment protocols. The initial recommended treatments for recluse spider bites includes cleaning the bite site, cold compresses, elevation, immobilization, analgesics, antihistamines and tetanus prophylaxis.12,13 There are other treatment modalities, none of which randomized control studies have shown to provide clinical benefit. These treatments include antibiotics, glucocorticoids, hyperbaric oxygen, surgical intervention and nitroglycerin.
Antibiotics. Dapsone (Aczone, Allergan) has been in use for several decades in the treatment of recluse spider bites. Physicians presumed that dapsone stopped dermonecrosis by inhibiting leukocyte migration, degranulation and cytokine release.14 Animal studies have shown conflicting results and currently there are no studies demonstrating the clinical efficacy of dapsone for the treatment of recluse spider bites.2,15 Additionally, dapsone carries a risk of hemolysis with methemoglobinemia. Authors suspect that dapsone may be effective in treating recluse spider bites that physicians had misdiagnosed as infections.10
Glucocorticoids. One may use both systemic and intralesional glucocorticoids to treat recluse spider bites. Oral glucocorticoids may relieve many of the systemic symptoms that result from recluse spider bites, but intralesional injections have no benefit and can actually delay wound healing.16,17
Hyperbaric oxygen. Hyperbaric oxygen hypothetically slows the dermonecrosis of recluse bites by oxidizing bonds and inhibiting the spider’s hemotoxic venom. Studies evaluating the effect of hyperbaric oxygen for the treatment of recluse spider have shown mixed treatment outcomes with some studies showing clinical benefits and other studies showing no effect18-22
Surgical intervention. Studies have shown no clinical benefit and possible worse clinical outcomes with early surgical excision for the treatment of recluse spider bites.23 Early surgical excision can extend the dermonecrosis and lead to complications including delayed wound healing, secondary infection and scarring.13,14 For larger areas of dermonecrosis resulting from recluse spider bites, delayed surgical intervention including debridement, excision of eschars and split thickness skin grafting may be required.13,14
Nitroglycerin. Nitroglycerin is a suggested treatment to counteract the vasoconstrictive effect of recluse spider bite venom, but animal studies show no benefit of nitroglycerin in decreasing necrosis and that nitroglycerin treatment can lead to increased inflammation and signs of systemic loxoscelism.24
In conclusion, while recluse spider bites are relatively uncommon, they are clinically significant due to their potential to cause dermonecrosis at the bite site. While most recluse spider bites are minor and spontaneously resolve, they can lead to both necrotic cutaneous loxoscelism and viscerocutaneous loxoscelism. There are numerous infectious and noninfectious conditions that can produce necrotic wounds similar to the recluse spider bite. Methicillin-resistant Staphylococcus aureus infection is one of the most common disorders misdiagnosed as a recluse spider bite.
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