Black widow spider bite

Background

Black widow spider
  • Identification: red hourglass on otherwise black spider
  • Genus: Latrodectus

Mechanism

Envenomation with ‎α-Latrotoxin causes massive release of neurotransmitters norepinephrine, dopamine, acetylcholine, glutamate and GABA from the nerve terminals causing muscle cramps, tachycardia and hypertension

The massive release of neurotransmitters leads to the clinical envenomation syndrome known as latrodectism.

Clinical Features

Grading System

  • Grade 1: Range from no symptoms to local pain at the envenomation site with normal vital signs
  • Grade 2: Involve muscular pain at the envenomation site to migration to the trunk, diaphoresis at bite site and normal vital signs
  • Grade 3: Include grade 2 with abnormal vital signs; diaphoresis distant to envenomation site, generalized myalgias to back, chest and abdomen, nausea vomiting and headaches.

Local

  • Pinprick sensation; then increasing local pain that may spread to entire extremity
  • Erythema appears 20-60 min after the bite
  • Pain begins to abate after several hours and disappears by 2-3d

Systemic

Differential Diagnosis

Envenomations, bites and stings

Diagnosis

  • Typically clinical

Management

  • Local wound care and tetanus prophylaxis are essential.
  • Routine antibiotic use is not indicated.
  • Pain and muscle spasms
    • Grade 1: Cold packs and NSAIDS
    • Grade 2/3: IV Opioids and Benzos
  • Systemic illness
    • Antivenin
      • Antivenin Latrodectus Mactans
        • Dosage: The usual dose is one to two vials diluted in 50 to 100 mL 5% dextrose or 0.9% sodium chloride solution, with the combination infused over 1 hour.
        • Controversial: Morbidity (pain, cramping and autonomic disturbances) are high, but mortality is low. The antivenin is horse serum derived, can lead to anaphylaxis and serum sickness.
      • Consider for:
        • Children
        • Pregnant women
        • Elderly

Disposition

  • Consider admission for:
    • Symptoms of moderate envenomation
    • Pregnant women
    • Children
    • Pts w/ preexisting cardiovascular disease or HTN

See Also

External Links

References