Brown Recluse Spider

Aka: Brown Recluse Spider, Recluse Spider, Fiddleback Spider, Loxosceles reclusa, Loxoscelism, Loxosceles Spider, Brown Recluse Spider Bite, Poisoning due to Brown Recluse Spider Venom, Genus Loxosceles

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II. Types: Recluse Spider scientific names

  1. Loxosceles arizonica
  2. Loxosceles deserta
  3. Loxosceles devia
  4. Loxosceles laeta
  5. Loxosceles rufescens
  6. Loxosceles reclusa

III. Epidemiology

  1. Spiders are most abundant and active on warm nights
  2. Bites are most common in early morning hours (Brown recluse is nocturnal)
  3. Recluse Spiders
    1. Eleven Loxosceles Spider species in North America (including Brown Recluse or Loxosceles reclusa)
    2. Other Recluse Spiders worldwide
      1. Siz-Eyed Sand Spider
        1. Southern African Spider (related to Brown Recluse Spider)
      2. Chilean Recluse Spider (arana de rincon, aranha-marrom, corner Spider)
        1. Most dangerous of the Recluse Spiders
  4. Brown Recluse Spiders (Loxosceles reclusa) distribution
    1. South America
    2. Southern United States (South of I-80)
      1. Southern half of Iowa, Ilinois and Ohio
      2. East through Kentucky, Tennessee and Georgia
      3. West through Kansas, Oklahoma, and Texas

IV. Mechanism: Toxicity

  1. Autoimmune response from Cytokines, Neutrophil activation and Lymphocytes
  2. Venom induced cytotoxicity
    1. Contains phospholipase enzyme (Sphingomyelinase D) which degrades extracellular matrix
    2. Results in local and sometimes systemic reaction

V. Pathophysiology

  1. Brown Recluse Spider identification
    1. Males are non-descript brown Spiders
    2. Small Spiders (typically up to 2 to 2.5 cm) compared with the medium sized black widows (up to 4 cm in size)
    3. Three pair of eyes in dyads (one pair anterior, and the other 2 pairs are lateral to either side)
      1. Most Spiders instead have 4 pair of eyes in 2 rows
    4. Females are more distinctive
      1. Thin torso
      2. Larger leg spans (20 to 30 mm)
      3. Darker brown on the dorsal body
      4. Dorsal pattern on the thorax resembles a fiddle (or inverted violin)
        1. Not visible in young Spiders, and faded in older Spiders
  2. Circumstances
    1. Spiders hide indoors in quiet, warm, dark areas (e.g. piles of clothing, behind furniture)
    2. Spiders are not aggressive unless Antagonized
      1. Person rolls over them in bed sheets or clothing
      2. Outdoor disturbed habitat (e.g. wood piles, storage containers)
    3. Bed linens or bedclothes squeeze Spider against skin
    4. Most common bite sites
      1. Axilla
      2. Waist
      3. Foot and ankles (under socks)

VI. Signs: Local bite site (cutaneous Loxoscelism)

  1. Hours 1-3
    1. Minimally painful, pruritic bite initially
    2. Erythematous Plaque or Papule forms and resolves without associated swelling
  2. Hours 3-12
    1. Tender, red, violaceous or hemorrhagic halo forms around bite site
    2. Center or halo may be pale due to vasospasm
  3. Hours 12-24
    1. Painful wound site edema
    2. Wound site erythema may become irregular (as venom spreads with gravity)
    3. Localized vessicles or bullae may develop at bite site
  4. Hours 24 to 72 hours
    1. Central necrosis (10% to 40% of cases, Necrotic Arachnidism)
  5. Days 5 to 7
    1. Non-necrosed lesions heal within 1 week
    2. Dry necrotic eschar forms
  6. Weeks 2 to 3
    1. Eschar separates with underlying ulceration (may expose underlying Muscle fascia)
    2. Healing over months, with scarring in 13% of cases

VII. Signs: Systemic Loxoscelism (Viscerocutaneous Loxoscelism)

  1. General
    1. Serious systemic reactions are uncommon with Brown Recluse (more common with arana de rincon)
  2. Mild Hemolysis
    1. Mild Hemolysis
    2. Mild Coagulopathy
  3. Severe Hemolysis (Viscerocutaneous Loxoscelism)
    1. Severe intravascular hemolytic syndrome
    2. Fever to 39-40 degrees Celsius
    3. Chills, Vomiting, and Joint Pain
    4. Hematuria
    5. Petechiae
    6. Measles-like toxic erythema rash

VIII. Differential Diagnosis

  1. General
    1. Brown Recluse Spider Bites are overdiagnosed
    2. Consider other causes of necrotic wounds (unless living in regions where Brown Recluse Spider Bites are common)
    3. Vetter (2002) Ann Emerg Med 39:544-6 [PubMed]
  2. Cellulitis
  3. Skin Abscess
  4. Diabetic Ulcer
  5. Syphilis
  6. Skin Cancer
  7. Pyoderma Gangrenosum
  8. Lyme Disease
  9. Erythema Migrans
  10. Cutaneous Anthrax

IX. Diagnosis: Findings suggestive of alternative diagnosis (Mnemonic: NOT RECLUSE)

  1. Numerous bite lesions
  2. Occurrence with non-classic trigger for recluse bite (e.g. gardening)
  3. Timing outside typical North American Recluse bite window (April to October)
  4. Red Center (instead of the typical pale, blue-white or purple center of a Recluse bite)
  5. Elevated (instead of the typical flat or sunken appearance of a recluse bite)
  6. Chronic Wound >3 months old
  7. Large wound diameter (>10 cm)
  8. Ulcerates too early (<7 days)
  9. Swelling ouside face and feet
  10. Exudative or pustular (unlike the dry Recluse bite wounds)
  11. Stoecker (2017) JAMA Dermatol 153(5): 377-8 [PubMed]

X. Labs

  1. Complete Blood Count and Peripheral Smear
    1. Hemolytic Anemia
    2. Thrombocytopenia
  2. ProTime (PT)
  3. Partial Thromboplastin Time (PTT)
  4. Urinalysis for Myoglobinuria
  5. Coombs test
  6. Creatine Kinase
  7. Comprehensive metabolic panel
  8. Fibrinogen
  9. D-Dimer
  10. Electrocardiogram

XI. Management

  1. Initial symptomatic relief
    1. Ice packs to wound (on for 20 min per hour)
      1. Sphingomyelinase toxin is inactivated by cold
      2. Ice prevents further Skin Injury (including necrosis)
    2. Analgesics
    3. Elevate extremity with bite site
    4. Antihistamines
      1. Cetirizine (Zyrtec) 10 mg orally once to twice daily (for age over 12 years)
  2. Additional wound care measures
    1. Basic wound care and cleansing with soap and water of site
    2. Debride necrotic tissue
    3. Antibiotics if signs of Cellulitis
      1. Consider wound culture
    4. Tetanus Prophylaxis
    5. Consider referral to plastic surgery for wound check on follow-up
  3. Specific Local Therapies
    1. No specific therapy has been shown to be beneficial
    2. Antitoxin is not available outside of South America (esp. Brazil)
    3. Avoid ineffective or unsupported treatments
      1. Avoid Leukocyte inhibitors (Colchicine)
      2. Avoid hyperbaric oxygen (no evidence to support as of 2017)
      3. Dapsone use is controversial
        1. May considered in severe cases (e.g. Chilean Recluse Spider)
        2. Dose: 50-100 mg twice daily for 10 days
        3. Postulated to decrease Neutrophil degranulation and necrosis
        4. Do not use if G6PD positive (due to Hemolytic Anemia risk; test first)
    4. Avoid early local procedures (spreads necrosis)
      1. Avoid early local Corticosteroid Injection
      2. Avoid early lesion excision
        1. Consider later with grafting if scarring present
        2. Scar revision may be considered after necrosis has resolved
  4. Severe hemolytic systemic reaction
    1. Systemic Corticosteroids
    2. Organ specific supportive therapies
  5. Disposition
    1. May discharge home if only local symptoms

XII. Course

  1. Anticipate healing over 1-8 weeks
  2. Major scarring at wound site occurs in 10-15% of cases

XIII. Prevention

  1. Shake clothes out before putting on

XIV. Complications

  1. Acute Hemolysis (esp. children with extensive skin involvement)
  2. Acute Tubular Necrosis (and Acute Renal Failure)
  3. Disseminated Intravascular Coagulation (DIC)

XV. References

  1. Cowling and Ferreri (2019) Crit Dec Emerg Med 33(2): 17-25
  2. Cowling and Lowes (2024) Crit Dec Emerg Med 38(1): 4-13
  3. Lin and Miguel in Herbert (2018) EM:Rap 18(1): 17-9
  4. Cacy (1999) J Fam Pract 48(7):536-42 [PubMed]
  5. Diaz (2007) Am Fam Physician 75(6):869-73 [PubMed]
  6. Herness (2022) Am Fam Physician 106(2): 137-47 [PubMed]
  7. Juckett (2013) Am Fam Physician 88(12): 841-7 [PubMed]
  8. Swanson (2005) N Engl J Med 352:700-7 [PubMed]

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