A complete blood count, including platelet count and differential, will allow the provider to observe for disseminated intravascular coagulation, hemolysis, and thrombocytopenia. The abnormal results most commonly found in patients who have sustained a brown recluse spider bite are leukocytosis and an elevated erythrocyte sedimentation rate. A skin biopsy of the site may reveal the presence of eosinophils, neutrophils, and thrombosis, all of which support the diagnosis of a brown recluse spider bite.2
A valid, reliable test to detect Loxosceles venom is needed in the clinical setting; the differential diagnosis for brown recluse spider bites is broad (see the table1,6,11,13-15 below), and diagnostic error can occur, delaying appropriate treatment for the actual presenting condition—which could be debilitating or in rare cases, fatal.16 One test for Loxosceles venom, though not currently marketed for use in humans, shows potential. It is a polyclonal enzyme-linked immunosorbent assay (ELISA) with a demonstrated ability to detect venom in rabbits for as long as seven days after injection.7 Further refinement of the polyclonal ELISA is under way in efforts to increase its sensitivity and specificity.17
Diagnosis of a brown recluse spider bite is difficult at best. Other potential causes of the associated presenting symptoms should be excluded before a brown recluse spider bite is considered confirmed.
Several factors add to the difficulty of diagnosing a brown recluse bite. Oftentimes it may take the patients days or weeks after the bite to see a health care provider, and they rarely present with the spider that bit them (or that they believe bit them).1 Currently, the only true standard for proof of envenomation by a brown recluse is to collect the spider and have its identify verified by an entomologist or other expert—not necessarily the health care provider.
One condition that is frequently misdiagnosed as a brown recluse bite is methicillin-resistant Staphylococcus aureus infection (MRSA; see Figure 2b). Misdiagnosis as a bite will delay appropriate treatment for MRSA and possibly lead to transmission of infection to others, as the unaware patient does not take proper precautions to avoid spreading MRSA to others.7 Patients with MRSA who experience significant tissue eradication or tissue death, or who have developed systemic symptoms, are candidates for hospitalization and possibly surgical debridement.2
Even without proper verification that the lesion is the bite of a brown recluse, it remains essential to provide basic treatment—initially, to wash the area with mild soap and water, then elevate the affected extremity and apply ice; rest is recommended.12 The patient’s tetanus immunization status should be verified, with tetanus vaccine administered if appropriate.7,11
While most brown recluse bites will resolve without major treatment within two to three months, disabling manifestations warrant treatment. Treatment goals are to keep the skin intact, decrease the likelihood that infection will spread, and maintain circulation to the affected area.
Several treatment options are possible for a confirmed brown recluse spider bite with envenomation. Oral dapsone, initiated within 36 hours, has been shown to reduce or delay the need for surgical intervention in cases of severe necrotic arachnidism.2,13,18,19 Dosage ranges from 50 mg/d to 100 mg/d, divided bid for adults; and for children, 1.0 to 2.0 mg/kg/d, not to exceed 100 mg/d.3
Before dapsone is prescribed or administered, the patient must be tested for glucose-6-phosphate dehydrogenase (G6PD) deficiency, as dapsone use in such individuals can lead to hemolysis.3,20 Clinicians unfamiliar with this medication should request a consultation with an expert (eg, in infectious disease, wound care, pharmacology) regarding treatment and the need for monitoring potential adverse effects. Additionally, although dapsone has been recommended for this indication for longer than 20 years, few human studies have been reported to support its use.19
The anti-inflammatory effects of steroids may be useful in some cases, as they may provide red blood cell membrane–stabilizing effects in patients with systemic loxoscelism.7 Although no guideline currently exists for dosing of glucocorticoids in spider bite treatment, a shorter period of eschar duration was reported in one animal study involving methylprednisolone administered within two hours of inoculation, dosed at 2 mg/kg of body weight initially, then daily for two days longer.11
Antibiotics may minimize the inflammatory reaction at the bite site, although generally, antibiotics are reserved for infections and not recommended for prophylaxis. Antihistamines may be used to relieve minor symptoms related to histamine release (eg, itching) and also for treatment of anaphylaxis.3 Analgesics, such as acetaminophen, may be prescribed for minor discomfort. Clinicians should individualize medication use (both drug and dose) based on the needs of the patient.
Hyperbaric oxygen therapy, a modality commonly used in wound healing, has been theorized to break down sphingomyelinase-D, thus preventing further spread of venom.1,21 In patients treated with this modality for brown recluse bites, reported results have been mixed.7