Envenomation

Hymenoptera stings

• Clinical Presentations:
  • Local Reaction: Minor erythema, edema (< 5 cm), sharp pain; resolves in hours.
  • Large Local Reaction (LLR): IgE-mediated contiguous swelling (> 10 cm) peaking at 24–48h; sterile inflammation often confused with cellulitis. c
  • Systemic (Anaphylaxis): Urticaria, angioedema, stridor/wheezing, GI cramps, hypotension/shock.
  • Toxic Envenomation (> 50–100 stings): Direct toxin load causing rhabdomyolysis, hemolysis, and ATN/AKI.
• Diagnosis:
  • Acute: Purely clinical diagnosis; obtain serum tryptase only if diagnosis is ambiguous.
  • Post-Acute Workup: Venom-specific skin testing or venom-specific serum IgE.
    • Must be delayed ≥ 4–6 weeks post-sting to avoid false negatives (refractory anergic period).
    • Indicated only for patients with prior systemic/anaphylactic reactions (not for isolated local/LLRs).
• Differential Highlights:
  • Cellulitis: Indolent onset (> 48–72h), fever, purulence, ascending lymphangitis (LLR is sterile and peaks early). c
  • Brown Recluse Spider: Necrotic ulcer with central violaceous blanching (“bull’s-eye” lesion).
  • Black Widow Spider: Dual puncture marks, severe muscle spasms, rigid “board-like” abdomen.
• Acute Management:
  • 1st-Line (Life-Saving): IM Epinephrine (1:1000) in the anterolateral thigh (0.3–0.5 mg in adults; 0.01 mg/kg in kids); repeat q5–15min PRN.
  • Airway/Breathing: High-flow O2, early endotracheal intubation if stridor/hoarseness develops, inhaled albuterol for bronchospasm.
  • Circulation: Aggressive IVF boluses (1–2 L isotonic crystalloid) for hypotension; place patient supine/elevate legs.
  • Adjuncts (Never delay Epinephrine): IV H1/H2-blockers, systemic corticosteroids (reduce biphasic risk).
  • Refractory/Special Case: IV Glucagon for patients on beta-blockers with refractory hypotension.
  • Local/LLR Care: Scrape stinger, cold compresses, oral NSAIDs/antihistamines; short-course PO prednisone for severe LLR (no routine antibiotics).
• Disposition & Long-Term Prevention:
  • Observation: Monitor in ED for 4–8 hours to rule out biphasic reactions.
  • Discharge: Prescribe two Epinephrine auto-injectors (EpiPens) and provide administration training.
  • Venom Immunotherapy (VIT):
    • Indicated for systemic anaphylaxis + positive skin/IgE test.
    • Reduces recurrent anaphylaxis risk from 30–60% down to < 5%.
    • Not indicated for isolated cutaneous reactions in children < 16 years or isolated LLRs.