Black widow spider bite

Background

Black widow spider

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

Mechanism

Envenomation causes massive release of neurotransmitters norephedrine, 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

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

Differential Diagnosis

Envenomations, bites and stings

• Hymenoptera stings (bees, wasps, ants)
• Mammalian bites
  • Closed fist infection (Fight bite)
  • Dog bite
• Marine toxins and envenomations
  • Toxins (ciguatera, neurotoxic shellfish poisoning, paralytic shellfish poisoning, scombroid, tetrodotoxin
  • Stingers (stingray injury)
  • Venomous fish (catfish, zebrafish, scorpion fish, stonefish, cone shells, lionfish, sea urchins)
  • Nematocysts (coral reef, fire coral, box jellyfish, sea wasp, portuguese man-of-war, sea anemones)
  • Phylum porifera (sponges)
  • Bites (alligator/crocodile, octopus, shark)
• Scorpion envenomation
• Reptile envenomation
  • Snake bites
    • Crotaline (Pit Vipers)
    • Elapidae (Coral Snakes)
  • Lizard bites
• Spider bites
  • Black widow
  • Brown recluse
  • Tarantula
  • Funnel-web spider bite
  • Armed spider bite

Diagnosis

• Typically clinical

Management

• Pain and muscle spasms
  • Grade 1: Cold packs and NSAIDS
  • Grade 2/3: IV Opioids and Benzos
• Systemic illness
  • Antivenin
    • 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

• Bites and Stings