Black widow spider bite

Background

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

Black widow spider

Mechanism

• α-Latrotoxin envenomation causes massive release of neurotransmitters (norepinephrine, dopamine, acetylcholine, glutamate and GABA) from the nerve terminals → muscle cramps, tachycardia, hypertension
• This clinical envenomation syndrome is known as latrodectism

Clinical Features

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

• Muscle cramp-like spasms in large muscle groups (although exam rarely reveals rigidity)
• Pain becomes generalized
  • Severe abdominal wall musculature pain and cramping
• Headache, nausea/vomiting, diaphoresis, photophobia, dyspnea
• A-fib, myocarditis, priapism, and death are rare

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.

Differential Diagnosis

Envenomations, bites and stings

• Mammalian bites
  • Closed fist infection (Fight bite)
• Hymenoptera stings (bees, wasps, ants)
• Spider bites
  • Brown recluse
  • Black widow
  • Tarantula
• Scorpion envenomation
• Marine toxins and envenomations
• Snake bites
  • Crotaline (Pit Vipers)
  • Elapidae (Coral Snakes)

Evaluation

• Generally clinical diagnosis

Management

• Local wound care, analgesia and tetanus prophylaxis are mainstays of treatment
  • Grade 1: Cold packs and NSAIDs
  • Grade 2/3: IV Opioids and Benzodiazepines
• Antivenin - indicated for systemic illness only
  • Dosage: Usual dose is one to two vials diluted in 50 to 100 mL 5% dextrose or 0.9% sodium chloride, then infused over 1 hour
  • Use is controversial - Morbidity (pain, cramping and autonomic disturbances) are high, but mortality is low. Antivenin is horse serum derived, and can lead to anaphylaxis and serum sickness
  • Consider for: Pediatric patients, pregnant women, elderly

Not Indicated

• Routine antibiotic use is not indicated
• IV calcium gluconate to reduce muscle spasm is an outdated therapy not favored by toxicologists

Disposition

• Generally may be discharged
• Consider admission for:
  • Symptoms of moderate or severe envenomation
  • Pregnant women
  • Children
  • Preexisting cardiovascular disease or hypertension

See Also

• Envenomations, bites and stings

References

Authors

Ross Donaldson