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)

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]

Local scorpion sting (Rhopalurus amazonicus Lourenço, Brazil).

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

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

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

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

Supportive care
- Cold compress to area of sting
- Analgesic and anti-inflammatory medications
- Benzodiazepines may help with agitation and muscle spasm
- Intubation for pulmonary symptoms is rare, but may be necessary
Atropine
- May be given for hypersalivation and respiratory distress caused
- Contraindicated for scorpion stings not indigenous to US (may exacerbate adrenergic effects)
- Alternatively, can administer glycopyrrolate
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]

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.

↑ ^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.
↑ Nelson, Lewis, and Lewis R. Goldfrank. Goldfrank's Toxicologic Emergencies. New York: McGraw-Hill Medical Division, 2014. Print.
↑ http://www.anascorp-us.com/hospital/ Accessed 08/03/15
↑ http://www.fda.gov/ForConsumers/ConsumerUpdates/ucm266515.htm
↑ http://www.azcentral.com/news/articles/2011/11/10/20111110scorpion-drug-cost.html

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