Scorpion envenomation

Background

Arizona Bark Scorpion, (Centruroides sculpturatus)

• Most scorpion stings in North America result only in local pain.
• Arizona Bark Scorpion, Centruroides sculpturatus, found in AZ, NV, NM, TX, and CA, is the only neurotoxic species found in North America and can cause systemic toxicity.

Pathophysiology

Four neurotoxins, designated toxins I to IV, have been isolated from C. exilicauda. These toxins target excitable membranes especially at the neuromuscular junction, by opening sodium channels. This results in repetitive depolarization of nerves in both sympathetic and parasympathetic nervous systems causing catecholamine and acetylcholine release.

Clinical Features

Local reaction

• Pain and paresthesias near envenomation site.
  • "Tap" test: severe local tenderness when affected area is lightly tapped

Systemic reaction

• Uncommon but can be severe, particularly in children
• Cranial nerve and somatic motor dysfunction can develop:
  • Abnormal roving eye movements, blurred vision, pharyngeal muscle incoordination
  • Hypersalivation, noncardiac pulmonary edema (can → respiratory distress/failure)
  • Tongue fasciculations and uncoordinated motor agitation (flailing or jerking extremities)
• Tachycardia, other dysautonomias, and severe agitation can also be present
• Without antivenom, symptoms typically last 24-48 hrs

Grades of Centruroides envenomation

• Grade 1 - Local pain and/or paresthesias at site of envenomation
• Grade 2 - Pain and/or paresthesias remote from the site of the sting, in addition to local findings
• Grade 3 - Either cranial nerve/autonomic dysfunction or somatic skeletal neuromuscular dysfunction
  • Cranial nerve dysfunction - Blurred vision, roving eye movements, hypersalivation, tongue fasciculations, dysphagia, dysphonia, problems with upper airway
  • Somatic skeletal neuromuscular dysfunction - Restlessness, severe involuntary shaking or jerking of the extremities that may be mistaken for a seizure
• Grade 4 - Combined cranial nerve/autonomic dysfunction and somatic skeletal neuromuscular dysfunction

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

• Generally clinical diagnosis
  • Be aware that a discrete scorpion bite site may not be clinically apparent.

Treatment

1. Supportive care
   • Cold compress to area of sting
   • Analgesic and anti-inflammatory medications
   • Benzodiazepines may help with agitation and muscle spasm
2. Atropine
   • May be given for hypersalivation and respiratory distress caused
     • Contraindicated for foreign scorpion stings because may exacerbate adrenergic effects
3. Anascorp antivenom (Centruroides immune Fab) - Only stocked by certain hospitals in Arizona, Nevada, and Utah
   • Resolves clinical syndrome within 4hr
   • Common side effects: vomiting, pyrexia, rash, nausea, and pruritus
   • Serious side effects: anaphylaxis
   • Costs approx $8000 over vial, needing 3-4 vials for treatment

Disposition

• Grade I or II envenomation may generally be discharged after 6 hours of observation in the ED without progression of symptoms.
• Grade III or IV envenomation likely requires antivenom administration and/or admission.

See Also

• Bites and Stings