|Guide to Scorpion Envenomation Treatment
For Medical Personnel
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 the southwestern United States, primarily Arizona and small parts of Texas, New Mexico, Nevada, and California.)
* Tityus - Central and 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
It is important to 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 their stingers. 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 envenomations 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 firing of neurons. 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 stings.
* In the US: In 2001, a total of 14,569 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.
* Internationally: Reliable statistics on scorpion envenomations 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 exilicauda) 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 venoms of Androctonus australis and Leiurus quinquestriatus are the most toxic. C exilicauda venom is low in toxicity compared to most scorpions of medical importance.
* 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).
* Local tissue effects vary among species.
o Minimal local tissue effects are present with Centruroides envenomation.
o Significant local tissue reaction rules out C exilicauda envenomation.
o 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:
o Sympathetic overdrive symptoms predominate, causing tachycardia, hypertension, hyperthermia, and pulmonary edema.
o Parasympathetic symptoms include hypotension, bradycardia, salivation, lacrimation, urination, defecation, and gastric emptying.
* Cranial nerve effects include the following:
o Classic roving or rotary eye movements, blurred vision, tongue fasciculations, and loss of pharyngeal muscle control may be observed.
o Difficulty swallowing combined with excessive salivary secretions may lead to respiratory difficulty.
* Somatic effects include the following:
o Restlessness and involuntary muscle jerking that can be mistaken for seizures have been described.
o 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.
o Cerebral infarction, cerebral thrombosis, and acute hypertensive encephalopathy have been described with a variety of Buthidae scorpion envenomations.
* The causes of scorpion envenomation are primarily accidental.
* 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/lipase tests should be included 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.
* Obtain a chest radiograph in cases of respiratory difficulty.
* Skin test
o Skin test results are positive if a urticarial wheal with surrounding erythema develops within 10 minutes.
o The test result may not be a reliable indication of immediate hypersensitivity.
* Obtain an electrocardiogram, if indicated.
* 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
o Grade I - Local pain and/or paresthesias at the site of envenomation
o Grade II - Pain and/or paresthesias remote from the site of the sting, in addition to local findings
o 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
o Grade IV - Combined cranial nerve/autonomic dysfunction and somatic nerve dysfunction
* Local poison control centers may assist in management of envenomations.
o Contact the American Association of Poison Control Centers (800-222-1222) to be connected to a local poison control center.
o 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.
o 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.
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 envenomations 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 pressors.
Drug Category: Antivenom -- 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 a controversial issue. Many researchers report decreased morbidity, mortality, and hospital stay with its use. These researchers believe that antivenom therapy cannot be matched by supportive care in severe Buthidae scorpion envenomations. Others suggest that adverse effects (eg, anaphylactic reactions, serum sickness) limit or contraindicate its use.
Until recently, the antivenom for stings by the bark scorpion was manufactured in the Antivenin Production Laboratory of Arizona State University. Although this antivenom is no longer being produced, limited supplies are still available. However, this antivenom is not FDA approved, and it is not available outside of Arizona. Use remains controversial, but many physicians recommend it in grade III and grade IV envenomations. It has been shown to produce rapid resolution of systemic symptoms but not to affect pain or paresthesias. Adverse effects include immediate and delayed hypersensitivity reactions. Initially, these reactions were rare, but they have increased in frequency. This leads some physicians to prefer supportive care only.
The US Food and Drug Administration has recently given preliminary approval for clinical trials to evaluate a Mexican antivenom (Alarcramyn, manufactured by Laboratorios Silanes) for use in the United States.
Scorpion antivenin (goat serum) -- Formerly manufactured by Arizona State University. Used to neutralize toxins from scorpions. Routine premedication with antihistamines (H1 and H2 blockers) is recommended. Pretreatment with epinephrine (1:1000) 0.25 mL SC can reduce acute adverse reactions, although the risks of epinephrine should be considered. Need for pretreatment with steroids is not likely to prevent immediate reactions but may be helpful later if continued antivenom is indicated, despite allergic reaction. No longer manufactured; however, limited supply may be available from ASU.
Grade I and grade II envenomation: Not recommended
Grade III and grade IV: 1 vial in saline IV over 30 min; repeat once prn
Pediatric Dose Administer as in adults
C - Safety for use during pregnancy has not been established.
Because anaphylaxis can occur whenever antivenom is given, appropriate therapeutic agents for treatment of anaphylaxis should be available for immediate use
Drug Category: Cardiovascular agents -- Used to elevate blood pressure and heart rate in patients who already have been adequately volume resuscitated but remain in shock.
Dopamine (Intropin) -- Stimulates adrenergic and dopaminergic receptors. Hemodynamic effect is dependent on the dose. Lower doses predominantly stimulate dopaminergic receptors that, in turn, produce renal and mesenteric vasodilation. Cardiac stimulation and renal vasodilation produced by higher doses.
2-5 mcg/kg/min IV; increase by 5-10 mcg/kg/min increments prn
Pediatric Dose Administer as in adults
Documented hypersensitivity; pheochromocytoma or ventricular fibrillation
Phenytoin, alpha- and beta-adrenergic blockers, general anesthesia, and MAOIs increase and prolong effects of dopamine
C - Safety for use during pregnancy has not been established.
Closely monitor urine flow, cardiac output, pulmonary wedge pressure, and blood pressure during infusion; before infusion, correct hypovolemia with whole blood or plasma as indicated; monitoring central venous pressure or left ventricular filling pressure may be helpful in detecting and treating hypovolemia
Epinephrine (Adrenaline) -- Has alpha-agonist effects that include increased peripheral vascular resistance, reversed peripheral vasodilatation, systemic hypotension, and vascular permeability. Beta-agonist effects of epinephrine include bronchodilatation, chronotropic cardiac activity, and positive inotropic effects.
1-10 mcg/min IV
0.1-1 mcg/kg/min IV
Documented hypersensitivity; cardiac arrhythmias or angle-closure glaucoma; local anesthesia in areas such as fingers or toes because vasoconstriction may produce sloughing of tissue; do not use during labor (may delay second stage of labor)
Increases toxicity of beta- and alpha-blocking agents and halogenated inhalational anesthetics
C - Safety for use during pregnancy has not been established.
Caution in elderly patients, prostatic hypertrophy, hypertension, cardiovascular disease, diabetes mellitus, hyperthyroidism, and cerebrovascular insufficiency; rapid IV infusions may cause death from cerebrovascular hemorrhage or cardiac arrhythmias; before administration, correct blood-volume depletion, if possible
Norepinephrine (Levophed) -- DOC. Vasopressors are indicated for persistent hypotension not responsive to judicious fluid loading and sodium bicarbonate.
0.05-0.15 mcg/kg/min infusion; titrate to effect
0.1-1 mcg/kg/min infusion; titrate to effect
Documented hypersensitivity; peripheral or mesenteric vascular thrombosis because ischemia may be increased and the area of the infarct extended; uncorrected hypovolemia
Interactions Chlorpromazine enhances the pressor response of norepinephrine by blocking the reflex bradycardia caused by norepinephrine
D - Unsafe in pregnancy
Correct blood-volume depletion, if possible, before administration; administer into a large vein because extravasation may cause severe tissue necrosis; caution in occlusive vascular disease; consider benefits vs risks if hypercapnia is present
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.
* Some clinicians discharge patients from the ED safely after treatment with USA-APL scorpion antivenin and complete resolution of their systemic symptoms.
* 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.
* 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.
* Respiratory arrest
* Cardiac arrest
* Defibrination after B tamulus stings
* Hemolysis after H lepturus stings
* Pancreatitis after T trinitatis stings
* Antivenom-associated reactions (see Antivenin)
* Renal failure
* Prognosis is dependent on many factors, including species of scorpion, patient health, and access to medical care.
* Most patients recover fully after scorpion envenomation.