AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

Envenomation from most scorpions results in a simple, painful, local reaction that can be treated with analgesics, antihistamines, and symptomatic/supportive care. This article focuses on scorpions that generally are considered more dangerous to humans. All of the potentially lethal scorpions belong to the family Buthidae, with the exception of one genus, Hemiscorpius, which belongs to the family Scorpionidae (ie, Ischnuridae). A triangular sternal plate helps distinguish Buthidae from other scorpion families in which the sternal plate is more pentagonal (see Image 3). Scorpions of medical significance include the following genera in the given distributions:

• Centruroides - Southern United States, Mexico, Central America, and the Caribbean (Centruroides exilicauda is found in Mexico and Centruroides sculpturatus is found in the southwestern United States, primarily Arizona and small parts of Texas, New Mexico, Nevada, and California.) The accepted taxonomy of the bark scorpion has changed over time. Either C exilicauda or C sculpturatus have been accepted at various times. However, recent evidence from biochemical, genetic and physiologic characterization of their venom suggests that they are two different species as listed above.
• Tityus - Central America, South America, and the Caribbean
• Buthus - Across the Mediterranean area, from Spain to the Middle East
• Mesobuthus - Throughout Asia
• Parabuthus - Western and southern Africa
• Buthotus (ie, Hottentotta) - Across southern Africa to southeast Asia
• Leiurus - Across northern Africa and the Middle East
• Androctonus - Northern Africa to southeast Asia

Note that scorpions may be found outside their natural range of distribution when inadvertently transported with items such as luggage.

Pathophysiology

Scorpions grasp prey with pincers, arch their tails over their bodies, and deliver venom with the stinger. They inject venom from glands located lateral to the tip of the stinger.

Scorpion venom may contain multiple toxins and other compounds. Venom composition is complex, and detailed discussion of its pharmacological effects is beyond the scope of this article. The most important clinical effects of envenomation are neuromuscular, neuroautonomic, or local tissue effects. The primary targets of scorpion venom are voltage-dependent ion channels, of which sodium channels are the best studied. Venom toxins alter these channels, leading to prolonged neuronal activity. Many end-organ effects are secondary to this excessive excitation. Autonomic excitation leads to cardiopulmonary effects observed after some scorpion envenomations. Somatic and cranial nerve hyperactivity results from neuromuscular overstimulation. Additionally, serotonin may be found in scorpion venom and is thought to contribute to the pain associated with scorpion envenomation.

Frequency

United States

In 2004, a total of 14,950 scorpion envenomations were reported to the American Association of Poison Control Centers. However, because of underreporting, this is probably an underestimation of the true number of stings.

International

Reliable statistics on scorpion envenomation are not available. Many potentially dangerous scorpions inhabit the underdeveloped or developing world. Consequently, numerous envenomations go unreported, and true incidence is unknown.

Mortality/Morbidity

Accurate worldwide data do not exist. The highest reported mortality rate is recorded in data from Mexico, with estimates as high as 1000 deaths in one year. In the United States, 4 deaths were reported in an 11-year period according to one source (Langley, 1997). However, no deaths were reported to the American Association of Poison Control Centers from 1983 to 1999. Only one death from the Arizona bark scorpion (C sculpturatus) has been reported since 1964 (Boyer, 2001). Ironically, the highest and lowest mortality estimates are associated with different species within the same genus of scorpion (Centruroides).

• Children and elderly persons have an increased risk of mortality.
• In terms of venom lethality, the venom of Androctonus australis and Leiurus quinquestriatus are the most toxic. C sculpturatus venom is low in toxicity compared with most scorpions of medical importance.

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• Pain and paresthesias often are present.
• Nausea and vomiting are common.
• Specimen identification by an entomologist may be helpful (if the scorpion can be captured safely).

Physical

• Local tissue effects vary among species.
• • Minimal local tissue effects are present with Centruroides envenomation.
  • Significant local tissue reaction rules out C exilicauda envenomation.
  • Tapping over the injury site (ie, tap test) may cause severe pain after a sting by C exilicauda.
• Tachycardia and other dysrhythmias are caused by autonomic effects primarily, although direct myocardial toxicity with arrhythmogenic effects has been described.
• Hypertension or hypotension may be present.
• The patient may have hyperthermia.
• Respiratory arrest and loss of protective airway reflexes are common causes of mortality.
• Pulmonary edema has been described and may be secondary to cardiogenic causes and to increased capillary permeability.
• Autonomic effects include the following:
• • Sympathetic overdrive symptoms predominate, causing tachycardia, hypertension, hyperthermia, and pulmonary edema.
  • Parasympathetic symptoms include hypotension, bradycardia, salivation, lacrimation, urination, defecation, and gastric emptying.
• Cranial nerve effects include the following:
• • Classic roving or rotary eye movements, blurred vision, tongue fasciculations, and loss of pharyngeal muscle control may be observed.
  • Difficulty swallowing combined with excessive salivary secretions may lead to respiratory difficulty.
• Somatic effects include the following:
• • Restlessness and involuntary muscle jerking that can be mistaken for seizures have been described.
  • Presence of true seizures in Centruroides envenomation is controversial and has not been proven to occur. Seizures are described in association with other scorpion envenomations.
  • Cerebral infarction, cerebral thrombosis, and acute hypertensive encephalopathy have been described with a variety of Buthidae scorpion envenomations.

Causes

• The causes of scorpion envenomation are primarily accidental.

DIFFERENTIALS

Section 4 of 11  

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• Differentials
• Workup
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• Follow-up
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Other Problems to be Considered

Seizures
Dystonia

WORKUP

Section 5 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Lab Studies

• Cases vary from those requiring no laboratory tests to scenarios requiring extensive hematologic, electrolyte, and respiratory analysis.
• Obtain a complete blood count (CBC), platelets, and coagulation parameters, as needed. Defibrination syndrome has been reported following Buthus tamulus stings. Hemiscorpius lepturus has been shown to cause severe hemolysis.
• Amylase and lipase levels should be checked in the event of Tityus trinitatis envenomation because pancreatitis is common.
• Electrolytes, blood urea nitrogen (BUN), creatinine, and urinalysis may be considered. Renal failure may occur secondary to hemoglobinuria from hemolysis (after H lepturus sting) or myoglobinuria from rhabdomyolysis.
• Creatine kinase (CK) and urine myoglobin may reveal rhabdomyolysis after severe muscle hyperactivity.
• Obtain arterial blood gas (ABG) measurements as indicated for respiratory distress or to determine acid/base status.

Imaging Studies

• Obtain a chest radiograph in cases of respiratory difficulty.

Other Tests

• Obtain an electrocardiogram, if indicated.

TREATMENT

Section 6 of 11  

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• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Prehospital Care

• Primary assessment of airway, breathing, and circulation takes precedence.
• Few studies have evaluated the utility of most first aid.
• The utility of negative pressure extraction devices has not been evaluated for scorpion stings.
• Perform endotracheal intubation and vascular access as needed.

Emergency Department Care

Supportive care is the backbone of treatment for systemic symptomatology.

• Grades of Centruroides envenomation
• • Grade I - Local pain and/or paresthesias at the site of envenomation
  • Grade II - Pain and/or paresthesias remote from the site of the sting, in addition to local findings
  • Grade III - 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 IV - Combined cranial nerve/autonomic dysfunction and somatic nerve dysfunction

Consultations

• Local poison control centers may assist in management of envenomations.
• • Contact the American Association of Poison Control Centers (800-222-1222) to be connected to a local poison control center.
  • The University of Arizona Poison and Drug Information Center (520-626-6016 from outside Arizona or 800-362-0101 from Arizona only) has special experience in Centruroides envenomation.
  • The Antivenom Index, published by the American Zoo and Aquarium Association and the American Association of Poison Control Centers, lists the locations, amounts, and various types of antivenom stores.

MEDICATION

Section 7 of 11  

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• Follow-up
• Miscellaneous
• Multimedia
• References

Analgesia may be indicated. Exercise caution when using narcotics for a patient with an unsecured airway because respiratory depressive effects may be synergistic with some scorpion venoms. Some recommend against using narcotics to treat scorpion envenomation with signs of systemic toxicity, especially in children. Tetanus prophylaxis is recommended if the patient cannot verify current status. Prophylactic antibiotic therapy is not required. Corticosteroids have not been shown useful in treating venom toxicity. Hypertensive emergencies may require standard antihypertensive therapy. Conversely, hypotension may require fluid resuscitation and/or vasopressors.

Cardiovascular agents can be used to elevate or decrease blood pressure and increase heart rate. Vasopressors and inotropic agents may be necessary in patients who already have been adequately volume resuscitated but remain in shock. Conversely, antihypertensives may be needed in patients with sympathetic-induced hypertension. No clear evidence exists as to which agent is most beneficial in specific circumstances. Autonomic instability from scorpion envenomation may lead to rapid, dramatic fluctuations in heart rate and blood pressure. Agents should be chosen with detailed knowledge of their pharmacology and understanding of the pathophysiology of scorpion venom described above. Ideally, the agents are effective, have rapid onset, can be titrated to effect, have a short half-life if discontinued, and have minimal side effects.

A total of 22 types of scorpion antivenom are listed in the American Zoo and Aquarium Association Antivenom Index. They are available for a number of different species and have varied efficacy. Antivenom use remains controversial. Many researchers report decreased morbidity, mortality, and hospital stay with its use. These researchers and clinicians believe that antivenom therapy cannot be matched by supportive care in severe Buthidae scorpion envenomation. Others suggest that adverse effects (eg, anaphylactic reactions, serum sickness) limit or contraindicate antivenom use.

Until recently, the antivenom for stings by the bark scorpion was manufactured in the Antivenin Production Laboratory of Arizona State University. Its use was controversial. It had been shown to produce rapid resolution of systemic symptoms but not to affect pain or paresthesias. Subsequently, many physicians recommended it in grade III and grade IV envenomations. Adverse effects included immediate and delayed hypersensitivity reactions. Initially, these reactions were rare, but they increased in frequency. This leads some physicians to prefer supportive care only, as they felt that the treatment was potentially worse than the disease. As death was rare if existent, they felt supportive care would yield similar outcomes. Currently, it is no longer being produced. Subsequently, an increased pediatric ICU admission rate of 500% is being reported with scorpion envenomation.

The US Food and Drug Administration has recently given approval for experimental use of a Mexican antivenom (Alarcramyn, manufactured by Instituto Bioclon), which is currently undergoing phase II clinical trials.

Drug Category: Toxoids

Wounds resulting from scorpion sting are at risk of Clostridium tetani infection. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome. Administer tetanus immune globulin (Hyper-Tet) to patients not immunized against C tetani products (eg, persons who have immigrated, elderly individuals).

Drug Category: Immune globulins

These agents induce passive immunity. Administer to patients not immunized against C tetani products (eg, persons who have immigrated, elderly individuals).

Drug Category: Antihistamines

Prevent the histamine response in sensory nerve endings and blood vessels. They are more effective in preventing histamine response than in reversing it.

Drug Name	Diphenhydramine (Benadryl, Benylin, Bydramine)
Description	Used for the symptomatic relief of allergic symptoms caused by histamine released in response to allergens.
Adult Dose	25-50 mg PO q6-8h prn; not to exceed 400 mg/d 10-50 mg IV/IM q6-8h prn; not to exceed 400 mg/d
Pediatric Dose	12.5-25 mg PO tid/qid or 5 mg/kg/d or 150 mg/m2/d PO divided tid/qid; not to exceed 300 mg/d 5 mg/kg/d or 150 mg/m2/d IV/IM divided qid; not to exceed 300 mg/d
Contraindications	Documented hypersensitivity
Interactions	Potentiates effect of CNS depressants; because of alcohol content, do not give syrup dosage form to patient taking medications that can cause disulfiramlike reactions
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	May exacerbate angle-closure glaucoma, hyperthyroidism, peptic ulcer, and urinary tract obstruction

Drug Category: Muscarinic antagonists

Current recommendations are for use in treating symptomatic bradycardias. Traditionally, its use to dry venom-induced, excess, respiratory secretions has been warned against because of its potential adverse cardiopulmonary effects. It may exacerbate pulmonary edema and hypertension and may lead to a subsequent tachycardia. A recent case series has suggested relative efficacy and safety with its use in 5 pediatric patients treated for C sculpturatus sting. However, this should be considered an area in need of further study rather than a change in recommendations.

FOLLOW-UP

Section 8 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Further Inpatient Care

• Patients with grade III or grade IV Centruroides stings and other severe Buthidae envenomations should be admitted to the intensive care unit (ICU) and/or treated with antivenom.
• Young children may not recover as quickly as adults after scorpion envenomation and are more likely to require observation.

Further Outpatient Care

• Patients with grade I or grade II Centruroides envenomations may be discharged. Discharge of patients with other Buthidae envenomations is more problematic because onset of systemic symptoms may be delayed up to 24 hours.
• Instruct patient regarding progression. Discuss symptoms of delayed serum sickness with patients treated with antivenom.

In/Out Patient Meds

• Give steroids and antihistamines if serum sickness develops.

Deterrence/Prevention

• Protective clothing, such as shoes or gloves, may prevent some scorpion envenomations.
• Shoes and equipment left outside in areas with indigenous scorpions should be checked for arthropods before use.

Complications

• Respiratory arrest
• Cardiac arrest
• Shock
• Seizures
• Rhabdomyolysis
• Death
• Defibrination after B tamulus stings
• Hemolysis after H lepturus stings
• Pancreatitis after T trinitatis stings
• Antivenom-associated reactions (see Antivenin)
• Renal failure

Prognosis

• Prognosis is dependent on many factors, including species of scorpion, patient health, and access to medical care.
• Most patients recover fully after scorpion envenomation.

MISCELLANEOUS

Section 9 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical/Legal Pitfalls

• Historically, scorpion envenomations were treated with a "lytic cocktail" of barbiturates and narcotics to decrease the hyperdynamic state and involuntary muscle activity.
• • However, this combination is no longer recommended because it may contribute to respiratory depression.
  • This is particularly pertinent for children and patients without a secured airway who exhibit systemic signs of envenomation.
• Some authors caution against narcotic use after certain scorpion envenomations because of possible synergistic effects on respiration between the narcotics and the venom. The authors recommend adequate treatment of pain with careful observation for excess sedation.
• • Likewise, concern exists for respiratory depression associated with benzodiazepine use. However, a retrospective chart review showed a midazolam drip to be safe and effective in patients with grade III or IV envenomation. This is especially important in light of the lack of antivenom available for use with C sculpturatus envenomation. The authors recommend treatment of symptoms with medication as necessary but with close monitoring in the ICU and securing the airway as needed.
• Atropine has been used to decrease respiratory secretions but, dangerously, may potentiate the sympathetic overdrive symptoms. However, it should be used in symptomatic bradycardia.
• Obtain informed consent before antivenom administration.

Special Concerns

• Special thanks are owed to Scott Stockwell, PhD, Medical Zoology Branch, Department of Preventive Medicine Services, US Army Medical Department Center and School for information on scorpion genera ranges.

MULTIMEDIA

Section 10 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Centruroides species. Note the slender pincers generally characteristic of scorpions from the family Buthidae. Photo by Sean Bush, MD.
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Media type:  Photo

Media file 2:  Centruroides limbatus, identified by Scott Stockwell, PhD. A small barb at the base of the stinger may be helpful in identifying Centruroides or Tityus species, although its presence is variable. Photo by Sean Bush, MD.
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Media type:  Photo

Media file 3:  Scorpions from the family Buthidae (which includes almost all of the potentially lethal scorpions) generally can be identified by the triangular sternal plate. In other families of scorpions, this feature is more square or pentagonal. Photo by Sean Bush, MD.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

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• Suchard JR, Hilder R. Atropine use in Centruroides scorpion envenomation. J Toxicol Clin Toxicol. 2001;39(6):595-8; discussion 599. [Medline].
• Valdez-Cruz NA, Davila S, Licea A, et al. Biochemical, genetic and physiological characterization of venom components from two species of scorpions: Centruroides exilicauda Wood and Centruroides sculpturatus Ewing. Biochimie. Jun 2004;86(6):387-96. [Medline].

Article Last Updated: Jan 4, 2007