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Scorpion Envenomation
Updated: Jul 24, 2008
Introduction
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 Media file 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 the Baja California peninsula of Mexico and Centruroides sculpturatus is found in the state of Sonora, Mexico and the southwestern United States, primarily Arizona and small parts of Utah, 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 southwest 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 2006, a total of 16,231 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 1 year. In the United States, 4 deaths were reported in an 11-year period according to one source.1 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 1964.2 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
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.
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Further Reading
Keywords
scorpion sting, scorpion envenomation, scorpion venom, Buthidae, Scorpionidae, Ischnuridae, Centruroides, Centruroides exilicauda, Tityus, Buthus, Mesobuthus, Buthotus, Buthus tamulus, Hottentotta, Leiurus, Leiurus quinquestriatus, Leiurus quinquestriatus, Androctonus, Androctonus australis, Hemiscorpius, Hemiscorpius lepturus
