Scorpion envenomation

Background

  • 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.[1]
Arizona Bark Scorpion, (Centruroides sculpturatus)

Pathophysiology

  • Four neurotoxins (toxins I to IV) have been isolated from C. exilicauda
  • Toxins target excitable membranes, especially at the neuromuscular junction, by opening sodium channels → repetitive depolarization of nerves in both sympathetic and parasympathetic nervous systems → catecholamine and acetylcholine release.[2]

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

Evaluation

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

Management

  • Supportive care
    • Cold compress to area of sting
    • Analgesic and anti-inflammatory medications
    • Benzodiazepines may help with agitation and muscle spasm
  • Atropine
    • May be given for hypersalivation and respiratory distress caused
    • Contraindicated for scorpion stings not indigenous to US (may exacerbate adrenergic effects)
  • Anascorp antivenom (Centruroides immune Fab) - Only stocked by certain hospitals in Arizona, Nevada, and Utah[3]
    • Resolves clinical syndrome within 4hr[4][1]
    • Common side effects: vomiting, pyrexia, rash, nausea, and pruritus
    • Serious side effects: anaphylaxis
    • Costs approximately $8000 per vial, and requires 3-4 vials for treatment[5]

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

References

  1. 1.0 1.1 Boyer LV, Theodorou AA, Berg RA, Arizona Envenomation investigators, et al. Antivenom for critically ill children with neurotoxicity from scorpion stings. N Engl J Med. 2009 May 14;360(20):2090-8.
  2. Nelson, Lewis, and Lewis R. Goldfrank. Goldfrank's Toxicologic Emergencies. New York: McGraw-Hill Medical Division, 2014. Print.
  3. http://www.anascorp-us.com/hospital/ Accessed 08/03/15
  4. http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm266515.htm
  5. http://www.azcentral.com/news/articles/2011/11/10/20111110scorpion-drug-cost.html