eMedicine Specialties > Emergency Medicine > Environmental

Scorpion Envenomation

David Cheng, MD, Assistant Professor of Emergency Medicine, Associate Emergency Medicine Residency Director, Associate Medical Director of Emergency Services, University of Arkansas Medical Sciences
Judith A Dattaro, MD, FACEP, Assistant Professor of Emergency Medicine in Surgery, Cornell University Medical College; Consulting Staff, Department of Emergency Medicine, Weill-Cornell University Medical Center, New York Presbyterian Hospital; Ramy Yakobi, MD, MBA, Medical Director of Emergency Department, Beth Israel/Kings Highway Division; Lecturer, Physician Assistant School, Cornell School of Medicine; Lecturer, Pre-hospital Management of Patient, Cornell/New York Presbyterian Hospital; Director of Emergency Department, New York Community Hospital

Updated: Aug 6, 2009

Introduction

Background

Scorpion stings are a major public health problem in many underdeveloped tropical countries. For every person killed by a poisonous snake, 10 are killed by a poisonous scorpion. In Mexico, 1000 deaths from scorpion stings occur per year. In the United States, only 4 deaths in 11 years have occurred as a result of scorpion stings. Furthermore, scorpions can be found outside their normal range of distribution, ie, when they accidentally crawl into luggage, boxes, containers, or shoes and are unwittingly transported home via human travelers.

A scorpion has a flattened elongated body and can easily hide in cracks. It has 4 pairs of legs, a pair of claws, and a segmented tail that has a poisonous spike at the end. Scorpions vary in size from 1-20 cm in length.

Out of 1500 scorpion species, 50 are dangerous to humans. Scorpion stings cause a wide range of conditions, from severe local skin reactions to neurologic, respiratory, and cardiovascular collapse. 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.

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.

Almost all of these lethal scorpions, except the Hemiscorpius species, belong to the scorpion family called the Buthidae. The Buthidae family is characterized by a triangular-shaped sternum, as opposed to the pentagonal-shaped sternum found in the other 5 scorpion families. In addition to the triangular-shaped sternum, poisonous scorpions also tend to have weak-looking pincers, thin bodies, and thick tails, as opposed to the strong heavy pincers, thick bodies, and thin tails seen in nonlethal scorpions. The lethal members of the Buthidae family include the genera of Buthus, Parabuthus, Mesobuthus, Tityus, Leiurus, Androctonus, and Centruroides. These lethal scorpions are found generally in the given distribution:

• Buthus - Mediterranean area, from Spain to the Middle East
• Parabuthus - Western and Southern Africa
• Mesobuthus – Throughout Asia
• Parabuthus - Western and southern Africa
• Buthotus (ie, Hottentotta) - Across southern Africa to southeast Asia
• Tityus - Central America, South America, and the Caribbean
• Leiurus - Northern Africa and the Middle East
• Androctonus - Northern Africa to Southeast Asia  
• 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.

However, these scorpions may be found outside their natural habitat range of distribution when inadvertently transported with luggage and cargo.

In general, scorpions are not aggressive. They do not hunt for prey; they wait for it. Scorpions are nocturnal creatures; they hunt during the night and hide in crevices and burrows during the day to avoid the light. Thus, accidental human stinging occurs when scorpions are touched while in their hiding places, with most of the stings occurring on the hands and feet.

Pathophysiology

Scorpions use their pincers to grasp their prey; then, they arch their tail over their body to drive their stinger into the prey to inject their venom, sometimes more than once. The scorpion can voluntarily regulate how much venom to inject with each sting. The striated muscles in the stinger allow regulation of the amount of venom ejected, which is usually 0.1-0.6 mg. If the entire supply of venom is used, several days must elapse before the supply is replenished. Furthermore, scorpions with large venom sacs, such as the Parabuthus species, can even squirt their venom.

The venom glands are located on the tail lateral to the tip of the stinger and are composed of 2 types of tall columnar cells. One type produces the toxins, while the other produces mucus. The potency of the venom varies with the species, with some producing only a mild flu and others producing death within an hour. Generally, the venom is distributed rapidly into the tissue if it is deposited into a venous structure. Venom deposited via the intravenous route can cause symptoms only 4-7 minutes after the injection, with a peak tissue concentration in 30 minutes and an overall toxin elimination half-life of 4.2-13.4 hours through the urine. The more rapidly the venom enters the bloodstream, the higher the venom concentration in the blood and the more rapid the onset of systemic symptoms.

Scorpion venom is a water-soluble, antigenic, heterogenous mixture, as demonstrated on electrophoresis studies. This heterogeneity accounts for the variable patient reactions to the scorpion sting. However, the closer the phylogenetic relationship between the scorpions, the more similar the immunological properties. Furthermore, the various constituents of the venom may act directly or indirectly and individually or synergistically to manifest their effects. In addition, differences in the amino acid sequence of each toxin account for their differences in the function and immunology. Thus, any modifications of the amino acid sequence result in modification of the function and immunology of the toxin.

Scorpion venom may contain multiple toxins and other compounds. The venom is composed of varying concentrations of neurotoxin, cardiotoxin, nephrotoxin, hemolytic toxin, phosphodiesterases, phospholipases, hyaluronidases, glycosaminoglycans, histamine, serotonin, tryptophan, and cytokine releasers. 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.

The most potent toxin is the neurotoxin, of which 2 classes exist. Both of these classes are heat-stable, have low molecular weight, and are responsible for causing cell impairment in nerves, muscles, and the heart by altering ion channel permeability.

The long-chain polypeptide neurotoxin causes stabilization of voltage-dependent sodium channels in the open position, leading to continuous, prolonged, repetitive firing of the somatic, sympathetic, and parasympathetic neurons. This repetitive firing results in autonomic and neuromuscular overexcitation symptoms, and it prevents normal nerve impulse transmissions. Furthermore, it results in release of excessive neurotransmitters such as epinephrine, norepinephrine, acetylcholine, glutamate, and aspartate. Meanwhile, the short polypeptide neurotoxin blocks the potassium channels.

The binding of these neurotoxins to the host is reversible, but different neurotoxins have different affinities. The stability of the neurotoxin is due to the 4 disulfide bridges that fold the neurotoxin into a very compact 3-dimensional structure, thus making it resistant to pH and temperature changes. However, reagents that can break the disulfide bridges can inactivate this toxin by causing it to unfold. Also, the antigenicity of this toxin is dependent on the length and number of exposed regions that are sticking out of the 3-dimensional structure.

Frequency

United States

A total of 13,000 stings have been reported, with the majority being from the nonlethal scorpions. Only 1 of 30 scorpion species found in the United States is dangerous to humans. This lethal scorpion species is the straw-colored Centruroides. Less than 1% of stings from Centruroides are lethal to adults; however, 25% of children younger than 5 years who are stung die if not treated. The epidemiological features of a patient who has been envenomed show a disposition for rural areas (73%), with most of the stings occurring in the summer months between 6:00 pm and 12:00 am (49%) and a second peak from 6:00 am to 12:00 pm (30%). Both of these peaks coincide maximum human activity with maximum scorpion activity. Furthermore, the larger the scorpion population, the larger the incidence rate. Because the offending scorpion is recovered for identification in only 30% of the cases, local knowledge of the type of scorpion populating the area is useful.

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

Scorpion stings occur in temperate and tropical regions, especially between the latitudes of 50°N and 50°S of the equator. Furthermore, stings predominantly occur during the summer and evening times. In addition, the majority of patients are stung outside their home.

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.

A recent 5-year surveillance study in Saudi Arabia found 6465 scorpion sting cases with a mean patient age of 23 years, a male-to-female ratio of 1.9, and a higher incidence of stings in the months of May-October.1

Mortality/Morbidity

Accurate worldwide data do not exist. The underreporting of scorpion stings is frequent because most envenomations occur in desert and jungle areas that do not have large medical facilities. Furthermore, reporting is not required.

Most deaths occur during the first 24 hours after the sting and are secondary to respiratory or cardiovascular failure.

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.² 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 1964.³ Ironically, the highest and lowest mortality estimates are associated with different species within the same genus of scorpion (Centruroides). 

Children and elderly persons are at the greatest risk for morbidity and mortality. A smaller child, a lower body weight, and a larger ratio of venom to body weight lead to a more severe reaction. A mortality rate of 20% is reported in untreated babies, 10% in untreated school-aged children, and 1% in untreated adults.

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.

Furthermore, patients in rural areas tend to fare worse than patients in urban areas because of the delay in getting medical help due to a longer travel time to medical centers. Fortunately, better public education, improved control of the scorpion population, increased supportive therapies, and more technologically advanced intensive care units have combined to produce a substantial decrease in mortality from these envenomations.

Race

No racial predilection exists. Any differences in individual reactions to the scorpion sting are a reflection of that individual's genetic composition rather than race.

Sex

Females are more susceptible than males to the same amount of scorpion venom because of their lower body weight.

Age

While adults are stung more often than children, children are more likely to develop a more rapid progression and increased severity of symptoms because of their lower body weight. Furthermore, elderly persons are more susceptible to stings because of their decreased physiologic reserves and increased debilitation.

Clinical

History

• For patients presenting with scorpion stings, ascertaining the following is essential:
  • Time of envenomation
  • Nature of the incident
  • Description of the scorpion:  Specimen identification by an entomologist may be helpful (if the scorpion can be captured safely).
  • Local and systemic symptoms: Pain and paresthesias often are present. Nausea and vomiting are common.
• The toxicity, variation, and duration of the symptoms depends on the following factors:
  • Scorpion species
  • Scorpion age, size, and nutritional status
  • Healthiness of the scorpion's stinging apparatus (telson)
  • Number of stings and quantity of venom injected
  • Depth of the sting penetration
  • Composition of the venom
  • Site of envenomation: Closer proximity of the sting to the head and torso results in quicker venom absorption into the central circulation and a quicker onset of symptoms.
  • Age of the victim
  • Health of the victim
  • Weight of the victim relative to amount of venom
  • Presence of comorbidities
  • Treatment effectiveness
• Generally, intrathecal and intravenous routes have immediate effects, while subcutaneous and intramuscular routes take effect several minutes to hours later.
• Nonlethal scorpion species tend to produce local reactions similar to a hymenopteran sting, while lethal scorpion species tend to produce systemic symptoms. The duration to progress to systemic symptoms ranges from 5 minutes to 4 hours after the sting. The symptoms generally persist for 10-48 hours.

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.

The signs of the envenomation are determined by the scorpion species, venom composition, and the victim's physiological reaction to the venom. The signs occur within a few minutes after the sting and usually progress to a maximum severity within 5 hours. The signs last for 24-72 hours and do not have an apparent sequence. Thus, predicting the evolution of signs over time is difficult. Furthermore, a false recovery followed by a total relapse is common.

A person who has been stung by a scorpion usually has 4 signs, with the most common being mydriasis, nystagmus, hypersalivation, dysphagia, and restlessness. The mode of death is usually via respiratory failure secondary to anaphylaxis, bronchoconstriction, bronchorrhea, pharyngeal secretions, and/or diaphragmatic paralysis, even though venom-induced multiorgan failure plays a large role.

Children present with the same symptoms and signs as adults, except their symptoms are more severe and protracted. Furthermore, they may display a restlessness that is out of proportion when compared to any other disease. A child's symptoms have been described as inconsolable crying; uncontrollable jerking of the extremities; and chaotic thrashing, flailing, and writhing combined with contorted facial grimaces. The symptoms mimic a centrally mediated seizure, but the patient is awake and alert the entire time.

The grading of these scorpion envenomations depends on whether or not neurological signs predominate and is as follows:

• Nonneurological predominance
  • Mild - Local signs
  • Moderate - Ascending local signs or mild systemic signs
  • Severe - Life-threatening systemic signs
• Neurologic predominance
  • Grade I - Local pain or paresthesia at the sting site (83%)
  • Grade II - Pain or paresthesia that has traveled from the sting site (9.1%)
  • Grade III - Either cranial nerve or somatic neuromuscular dysfunction (4.7%)
  • Grade IV - Both cranial nerve and somatic neuromuscular dysfunction (3%) 
• Local signs
  • Neurotoxic local effects
    • Local evidence of a sting may be minimal or absent in as many as 50% of cases of neurotoxic scorpion stings. In fact, tissue necrosis is rarely found.
    • A sharp burning pain sensation at the sting site, followed by pruritus, erythema, local tissue swelling, and ascending hyperesthesia, may be reported. This paresthesia feels like an electric current, persists for several weeks, and is the last symptom to resolve before the victim recovers.
    • The tap test is administered by tapping at the sting site. A positive result is when the paresthesia worsens with the tapping because the site is hypersensitive to touch and temperature. In fact, wearing clothing over the area and sudden changes in temperature exacerbate the symptoms. Tapping over the injury site (ie, tap test) may cause severe pain after a sting by C exilicauda.
  • Cytotoxic local effects
    • A macule or papule appears initially at the sting site, occurring within the first hour of the sting.
    • The diameter of the lesion is dependent on the quantity of venom injected.
    • The lesion progresses to a purpuric plague that will necrose and ulcerate.
    • Lymphangitis results from the transfer of the venom through the lymphatic vessels.
  • Nonlethal local effects
    • Pain, erythema, induration, and wheal may be present.
    • These are secondary to venom activation of kinins and slow-releasing substances.
    • Local tissue effects vary among species. Minimal local tissue effects are present with Centruroides envenomation. Significant local tissue reaction rules out C exilicauda envenomation.
• Neurologic signs: Most of the symptoms are due to either the release of catecholamines from the adrenal glands (sympathetic nerves) or the release of acetylcholine from postganglionic parasympathetic neurons. One study by Freire-Maia et al (1974) found that the adrenergic signs occur at a low venom dose, while cholinergic signs occur at high venom dose concentrations (ie, >40 mcg/100 g in Tityus serrulatus scorpion venom).4 Furthermore, the adrenergic phase tended to be more dependent on the venom dose than the cholinergic phase. However, dual manifestations of the adrenergic and cholinergic signs are possible because of varying organ system sensitivities to these neurotransmitters.
  • Central nervous system signs
    • Thalamus-induced systemic paresthesia occurs in all 4 limbs.
    • Patients experience venom-induced cerebral thrombosis strokes.
    • The level of consciousness is altered, especially with restlessness, confusion, or delirium.
    • Patients have abnormal behavior.
    • Ataxia is also a sign.
  • Autonomic nervous system signs - Predominately sympathetic signs, parasympathetic signs, or a combination of signs
    • Sympathetic signs
      • Hyperthermia
      • Tachypnea
      • Tachycardia
      • Hypertension
      • Arrhythmia
      • Hyperkinetic pulmonary edema
      • Hyperglycemia
      • Diaphoresis
      • Piloerection
      • Restlessness and apprehension
      • Hyperexcitability and convulsions
    • Parasympathetic signs
      • Bronchoconstriction
      • Bradycardia
      • Hypotension
      • Salivation, lacrimation, urination, diarrhea, and gastric emesis (SLUDGE)
      • Rhinorrhea and bronchorrhea
      • Goose pimple skin
      • Loss of bowel and bladder control
      • Priapism
      • Dysphagia
      • Miosis
      • Generalized weakness
    • Somatic signs
      • Rigid spastic muscle of the limbs and torso
      • Involuntary muscle spasm, twitching, clonus, and contractures
      • Alternating opisthotonos and opisthotonus from inactivation of sodium channels, leading to increased sodium and calcium uptake
      • Increased tendon reflexes, especially prolongation of the relaxation phase
      • Piloerection accompanied by goose pimples
  • Cranial nerve signs
    • Classic rotary eye movement may result in ptosis, nystagmus, and blurred vision.
    • Mydriasis is a sign.
    • Patients may have tongue fasciculations.
    • Dysphagia, dysarthria, and stridor occur secondary to pharyngeal reflex loss or muscle spasm.
    • Patients may present with excessive salivation and drooling.
  • Peripheral nervous system signs - Intense local burning pain with minimal swelling at sting site, followed by ascending numbness and tingling, then paralysis and convulsions
• Nonneurologic systemic signs
  • Cardiovascular signs - Usually follow a pattern of a hyperdynamic phase followed by a hypodynamic phase
    • Hypertension is described as follows:
      • Secondary to catecholamine and renin stimulation
      • Observed as early as within 4 minutes after the sting
      • Lasts a few hours
      • High enough to produce hypertensive encephalopathy
      • Hypotension - Less common and occurs secondary to excess acetylcholine or catecholamine depletion
    • Tachycardia is greater than 130 beats per minute, although bradycardia can be observed.
    • Transient apical pansystolic murmur is consistent with papillary muscle damage.
    • Cardiovascular collapse occurs secondary to biventricular dysfunction and profuse loss of fluids from sweating, vomiting, diarrhea, and hypersalivation.
      • Observed in 7-38% of cardiovascular cases
      • Mild envenomation - Vascular effect with vasoconstriction hypertension
      • Moderate envenomation - Left ventricular failure hypotension with and without an elevated pulmonary artery wedge pressure, depending on fluid status of the patient
      • Severe envenomation - Biventricular cardiogenic shock
      • Cardiac dysfunctions attributed to catecholamine-induced increases in myocardial metabolism oxygen demand (leading to myocardial ischemia–induced myocardial hypoperfusion) and to the direct effects of the toxin (leading to myocarditis)
  • Respiratory signs
    • Tachypnea may be present.
    • Pulmonary edema with hemoptysis and a normal-sized heart is observed in 7-32% of respiratory cases. This is secondary to a direct toxin-induced increased pulmonary vessel permeability effect and is also secondary to catecholamine-induced effects of hypoxia and intracellular calcium accumulation, which leads to a decrease in left ventricular compliance with resultant ventricular dilation and diastolic dysfunction.
    • Respiratory failure may occur secondary to diaphragm paralysis, alveolar hypoventilation, and bronchorrhea.
  • Allergic signs
    • Patients may have urticaria.
    • Angioedema is reported.
    • Patients may present with bronchospasm.
    • Anaphylaxis is possible.
  • Gastrointestinal signs
    • Patients may present with excessive salivation.
    • Dysphagia is possible.
    • Nausea and vomiting are reported.
    • Gastric hyperdistention occurs secondary to vagal stimulation.
    • Increased gastric acid output may lead to gastric ulcers.
    • Acute pancreatitis may lead to hyperglycemia.
    • Liver glycogenolysis may occur from catecholamine stimulation.
    • Toxic Hepatitis
  • Genitourinary signs
    • Patients have decreased renal plasma flow.
    • Toxin-induced acute tubular necrosis renal failure may occur.
    • Rhabdomyolysis renal failure may result from venom-induced excessive motor activity.
    • Priapism may occur secondary to cholinergic stimulation. One small study by Bawaskar (1982) found a positive prognostic correlation to the development of cardiac manifestations following scorpion stings.⁵
  • Hematological signs
    • Platelet aggregation may occur because of catecholamine stimulation.
    • Disseminated intravascular coagulation with massive hemorrhage may result from venom-induced defibrination.
  • Metabolic signs
    • Hyperglycemia may occur from catecholamine-induced hepatic glycogenolysis, pancreatitis, and insulin inhibition.
    • Increased lactic acidosis may occur from hypoxia and venom-induced increased lactase dehydrogenase activity.
    • Patients may have an electrolyte imbalance and dehydration from hypersalivation, vomiting, diaphoresis, and diarrhea.
  • Pregnancy signs - Toxin-induced uterine contraction
  • Symptoms predictive of hospital admission
    • Priapism (odds ratio 150.59)
    • Vomiting (odds ratio 15.82)
    • Systolic blood pressure (SBP) greater than 160 (odds ratio 13.38)
    • Temperature greater than 38º C (odds ratio 3.66)
    • Heart rate greater than 100 beats per minute (odds ratio 3.35)
• Symptomology of specific scorpion species
  • Mesobuthus, Tityus, and Leiurus - Tend to cause severe cardiovascular symptoms
  • Centruroides - Tend to cause neurological symptoms
  • Hemiscorpius - Tend to cause tissue necrosis

Causes

The causes of scorpion envenomation are primarily accidental. Scorpions are shy creatures and only sting if threatened, cornered, or disturbed (eg, being sat or stepped upon). Curious individuals are at risk because of increased interaction with the scorpion.

• The median lethal dose 50 (LD50) of various scorpion venoms in mg/kg of a subcutaneous injection into mice and the territorial distribution are listed below. Unfortunately, humans are much more sensitive than mice.
  • Leiurus quinquestriatus (Middle East) - 0.25 mg/kg
  • Androctonus crassicauda (Saudi Arabia) - 0.08-0.5 mg/kg
  • Centruroides noxius (Mexico) - 0.26 mg/kg
  • Androctonus mauritanicus (North Africa) - 0.32 mg/kg
  • Centruroides santa maria (Central America) - 0.39 mg/kg
  • Tityus serrulatus (Brazil) - 0.43 mg/kg
  • Buthus occitanus (North Africa) - 0.9 mg/kg
  • Centruroides sculpturatus (Southwest United States) - 1.12 mg/kg
  • Mesobuthus eupeus (Iran) - 1.45 mg/kg
• Generally, most lethal scorpions have an LD50 below 1.5 mg/kg.
• The average yield per scorpion via electrical excitation of the venom gland for a few species is listed below.
  • Tityus species - 0.39-0.62 mg
  • L quinquestriatus - 0.62 mg
  • Buthus species - 0.38-1.5 mg
• Milking the venom gland produces approximately a 4-fold increase in yield amount compared to electrical excitation.

Differential Diagnoses

Other Problems to Be Considered

Myasthenia gravis
Diphtheria
Guillain-Barré syndrome
Neuroleptic overdose
Sympathomimetic overdose
Venomous jellyfish, snake, and lizard envenomation
Seizures
Dystonia

Workup

Laboratory Studies

Scorpion envenomation cases vary from those requiring no laboratory tests to scenarios requiring extensive hematologic, electrolyte, and respiratory analysis.

• Obtain a CBC count for leukocytosis and hemolysis in patients with stings from the Hemiscorpius species. Hemiscorpius lepturus has been shown to cause severe hemolysis.
• Electrolyte evaluation is warranted in patients with venom-induced salivation, vomiting, and diarrhea.
• Coagulation parameters should be measured for venom-induced defibrination because, at high concentrations, the venom is an anticoagulant. Defibrination syndrome has been reported following Mesobuthus tamulus stings.
• Glucose levels should be measured to evaluate for hyperglycemia from liver and pancreas dysfunction.
• Creatine kinase and urinalysis help evaluate for venom-induced excessive motor rhabdomyolysis. Renal failure may occur secondary to hemoglobinuria from hemolysis (after H lepturus sting) or myoglobinuria from rhabdomyolysis
• Obtain amylase/lipase values to assess for pancreatitis, which is common, from Tityus trinitatis stings.
• Patients may have increased aspartate aminotransferase and alanine aminotransferase levels from venom-induced liver cell destruction.
• Increased catecholamine, aldosterone, renin angiotensin, and antidiuretic hormone levels are detected a few hours after the sting. The increased levels persist for 6 hours, after which a gradual decline occurs.
• Interleukin (IL)–1 levels are elevated in all envenomations.
• High levels of IL-6, interferon-gamma, and granulocyte-macrophage colony-stimulating factor are present in severe envenomations.
• Radiolabeled antibodies or immunoenzymatic assays help quantify the serum venom level because an association exists between the clinical signs of envenomation and this level.
• 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. Unilateral pulmonary edema may be seen on chest x-ray films because of the venom effect on pulmonary vascular permeability.
• Echocardiography findings are discussed as follows:
  • Echocardiography is more sensitive than electrocardiography and creatine kinase assays for assessing myocardial compromise after a scorpion sting.
  • Findings show a diffuse global biventricular hypokinesis with a decreased left and right ventricular ejection fraction of approximately 0.14-0.38. This dysfunction can appear just a few hours after the sting and usually normalizes within 4-8 days.
  • Serial echocardiography findings show that the return of left ventricular function to a normal state correlates to clinical cardiorespiratory improvement.
• Color-flow Doppler study findings show mitral incompetence, probably secondary to venom-induced dilated cardiomyopathy.

Other Tests

• Arterial blood gas determinations show a decrease in arterial oxygenation tension and an increase in PCO₂ within 15 minutes of the envenomation, findings consistent with mild metabolic acidosis.
• Pulmonary artery catheterization findings may include the following:
  • Elevated systemic vascular resistance occurs up to 4 times the normal level, with elevated mean arterial pressure (MAP) of 203 mm Hg.
  • Left ventricular failure produces a MAP of 57-69 mm Hg.
  • Biventricular failure produces a MAP of 47 mm Hg.
  • Low cardiac index occurs with elevated filling pressures.
• Perform serial spirometry measurements to help detect impending venom-induced diaphragmatic failure.
• Electrocardiography, if indicated
  • ECG changes persist for 10-12 days before normalizing.
  • ECG changes are observed in 63% of children who have been envenomated.
  • Rhythm disturbances are not dose-dependent but are related to the venom composition.
    • Sinus tachycardia - Most common rhythm
    • QTc prolongation - 53%
    • ST changes - 39%
    • T-wave inversion - 39%
    • Ventricular repolarization abnormalities - 15%
    • Bundle-branch block - 12.8%
    • First-degree block - 10.2%
  • A possible sequence of ECG changes has been noted. This sequence starts with bizarre, broad-notched, biphasic, peaked T waves with a beat-to-beat variation. This bizarre T wave is followed by the appearance of tiny Q waves and then atrioventricular dissociation with an accelerated junctional rhythm.

Procedures

• Cerebrospinal fluid pleocytosis is evident on spinal tap studies.

Histologic Findings

The local sting site shows mixed inflammatory cell infiltrates with eosinophils scattered among collagen bundles in an edematous dermis. Myocardial changes, which are most prominent at the papillary muscle and subendocardial region, include focal myocardial necrosis; myofibril destruction, especially at the I band; fine fatty deposits in the cardiac muscle fibers; interstitial edema; and increased cellularity, mainly lymphocytes and monocytes. Changes resemble interstitial hypoxia-induced myocarditis caused by large doses of catecholamines.

Treatment

Medical Care

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
• Androctonus australis Hector Hospitalization Score
  • Priapism: +3                               
  • Vomiting: +2                               
  • SBP >160: +2                              
  • Corticosteroid PTA: +2             
  • Temperature >38ºC: +1              
  • Heart rate >100 bpm: +1            

Total >2 = Hospitalization

• Although grading and scoring systems have been developed they are limited due to species specificity and low degree a symptoms that would lead to hospitalization or therapy.

Medical care

Because the clinical manifestations and severity of the symptoms vary among patients, individualize management of scorpion stings. Furthermore, frequent patient monitoring allows earlier recognition of the life-threatening problems of scorpion envenomation. Treatment generally consists of moving the patient away from the scorpion and stabilizing the patient's airway and vital signs, followed by administration of antivenin and institution of symptomatic and local treatment.

• Local treatment is discussed as follows:
  • A negative-pressure extraction device (ie, the extractor) may be useful, although the benefit is unproven. The extractor creates a negative pressure of 1 atm. Apply it to the sting site after incision. Oral extraction is contraindicated.
  • Use ice bags to reduce pain and to slow the absorption of venom via vasoconstriction. This is most effective during the first 2 hours following the sting.
  • Immobilize the affected part in a functional position below the level of the heart to delay venom absorption.
  • Calm the patient to lower the heart rate and blood pressure, thus limiting the spread of the venom.
  • For medical delay secondary to remoteness, consider applying a lymphatic-venous compression wrap 1 inch proximal to the sting site to reduce superficial venous and lymphatic flow of the venom but not to stop the arterial flow. Only remove this wrap when the provider is ready to administer systemic support. The drawback of this wrap is that it may intensify the local effects of the venom.
  • Apply a topical or local anesthetic agent to the wound to decrease paresthesia; this tends to be more effective than opiates.
  • Administer local wound care and topical antibiotic to the wound.
  • Administer tetanus prophylaxis.
  • Administer systemic antibiotics if signs of secondary infection occur.
  • Administer muscle relaxants for severe muscle spasms (ie, benzodiazepines.)
• Systemic treatment is instituted by directing supportive care toward the organ specifically affected by the venom.
  • Establish airway, breathing, and circulation (ie, ABCs) to provide adequate airway, ventilation, and perfusion.
  • Monitor vital signs (eg, pulse oximetry; heart rate, blood pressure, and respiratory rate monitor).
  • Use invasive monitoring for patients who are unstable and hemodynamic.
  • Administer oxygen.
  • Administer intravenous fluids to help prevent hypovolemia from vomiting, diarrhea, sweating, hypersalivation, and insensible water loss from a tropical environment.
  • Perform intubation and institute mechanical ventilation with end-tidal carbon dioxide monitoring for patients in respiratory distress.
  • For hyperdynamic cardiovascular changes, administration of a combination of beta-blockers with sympathetic alpha-blockers is most effective in reversing this venom-induced effect. Avoid using beta-blockers alone because this leads to an unopposed alpha-adrenergic effect. Also, nitrates can be used for hypertension and myocardial ischemia.
  • For hypodynamic cardiac changes, a titrated monitored fluid infusion with afterload reduction helps reduce mortality. A diuretic may be used for pulmonary edema in the absence of hypovolemia, but an afterload reducer, such as prazosin, nifedipine, nitroprusside, hydralazine, or angiotensin-converting enzyme inhibitors, is better. Inotropic medications, such as digitalis, have little effect, while dopamine aggravates the myocardial damage through catecholaminelike actions. Dobutamine seems to be a better choice for the inotropic effect. Finally, a pressor such as norepinephrine can be used as a last resort to correct hypotension refractory to fluid therapy.
  • Administer atropine to counter venom-induced parasympathomimetic effects.
• Insulin administration in scorpion envenomation animal experiments has helped the vital organs to use metabolic substrates more efficiently, thus preventing venom-induced multiorgan failure, especially cardiopulmonary failure. Unfortunately, no human studies have been conducted.
• Administer barbiturates and/or a benzodiazepine continuous infusion for severe excessive motor activity.
• The use of steroids to decrease shock and edema is of unproven benefit.
• Antivenin is the treatment of choice after supportive care is established. The quantity to be used is determined by the clinical severity of patients and by their evolution over time. Unfortunately, predicting the evolution of symptoms and, thus, the amount of antivenin that is needed in the future, is difficult.
  • The antivenin significantly decreases the level of circulating unbound venom within an hour. The persistence of symptoms after the administration of antivenin is due to the inability of the antivenin to neutralize scorpion toxins already bound to their target receptors.
  • Time guidelines for the disappearance of symptoms after antivenin administration are as follows:
    • Centruroides antivenin: Severe neurologic symptoms reverse in 15-30 min. Mild-to-moderate neurologic symptoms reverse in 45-90 min.
    • Non-Centruroides antivenin: In the first hour, local pain abates. In 6-12 hours, agitation, sweating, and hyperglycemia abate. In 6-24 hours, cardiorespiratory symptoms abate.
  • While an anaphylaxis reaction to the antivenin is possible, the patient is at lower risk for this than with other antivenins for other poisonous envenomations because of the huge release of catecholamines induced by the scorpion venom. However, the larger the dose of antivenin, the greater the chance for serum sickness.
  • In a prospective, randomized, double-blind study, Boyer et al compared scorpion-specific F(ab')₂ antivenom (Anascorp, Centruroides [scorpion] immune F(ab)₂ intravenous [equine], Instituto Bioclon) (n=8) with placebo (n=7)  in children who developed neurotoxic symptoms following scorpion envenomation. Neuromotor abnormalities were present in all patients at baseline, and respiratory distress was present in 20%. Beginning 2 hours after treatment, symptom resolution differed significantly in the antivenom group compared with the placebo group. Plasma venom concentrations were undetectable and cessation of the neurologic syndrome occurred within 4 hours in 100% of antivenom recipients compared with 1 placebo recipient (p=0.001). In this study, scorpion-specific F(ab')₂ antivenom successfully treated the clinical syndrome, reducing the need for concomitant sedation and reducing circulatingunbound venom levels.⁶
• A vaccine preparation was tried in experimental animals but was not pursued because of the need to prepare different antigens according to different geographical areas and to different species of scorpions living in the same area.
• In some cases, be aware that meperidine and morphine may potentiate the venom. Also, the concurrent use of barbiturates and narcotics may add to the respiratory depression in patients who have been envenomated.

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 jointly by the American Association of Poison Control Centers and the American Zoo and Aquarium Association, lists the locations, amounts, and various types of antivenom stores.

Activity

• Rest and immobilization of the sting site is recommended to prevent rapid absorption of the venom into the circulation.

Medication

The goals of pharmacotherapy are to reduce morbidity, to prevent complications, and to neutralize the toxin.

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. In particular, the use of the alpha-blocking agent prazosin has been used and recommended. However, all published evidence recommending for or against this agent has come from either retrospective observational or prospective cohort studies. A true randomized controlled trial of this agent has not been published. 

At this time, 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. Although many agents have rapid onset, they may also have prolonged effects. Should a hypertensive patient receive a longer-acting agent they may still have medication effects if they develop subsequent hypotension. In any case, 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.

Antivenins

Scorpion toxins are not good antigens because of small size and poor immunogenicity. They do not induce antibodies that cross-react against toxins of other scorpion species unless a 95% amino acid sequence homology exists between the 2 toxins. Thus, no universal antivenin is available. Instead, 22 types of scorpion antivenin exist.

Furthermore, the neurotoxin component of the scorpion venom tends to be the least immunogenic, resulting in the low efficiency for neurological complications. It usually is prepared from horses because they yield larger quantities. Sheep, goat, or bovine antivenin may be prepared if patient sensitivity to horse serum occurs.

A recent idea was to mix a batch of different scorpion antivenin together to create a universal antivenin, but this exposes the patient to unnecessary antivenin from scorpion species not from the patient's region.

Perform a skin test prior to administering the antivenin. First, dilute 0.1 mL of antivenin in a 1:10 ratio with isotonic sodium chloride solution. Second, administer 0.2 mL intradermally. A positive test result is if a wheal develops within 10 minutes. The skin test has a sensitivity of 96% and a specificity of 68%.

The best result occurs when antivenin is administered as early as possible (preferably within the first 2 h after the sting) and with adequate quantities to neutralize the venom (usually 50-100 times the LD50 amount). A decrease in curative effects occurs with longer sting-serotherapy delay and administration of insufficient amounts of antivenin.

USA-APL Centruroides scorpion antivenin

Used to neutralize toxins from scorpions. Produced in Arizona (for use in Arizona only). Not approved by FDA. Use remains controversial, but many physicians recommend it in grade III and IV envenomations. Shown to produce rapid resolution of systemic symptoms but does not affect pain or paresthesias. Results in resolution of symptoms within min to 2 h after administration. Antivenin treatment is based on venom burden, not patient's size. The smaller the victim, the more important it is to administer the full dose because of the venom dose-dependent severity.

Dosing

Adult

Grade I and II: None
Grade III and IV: 1 vial (5 mL) in 50 mL saline IV over 30 min; if severe symptoms still persist after 1 h, repeat once prn

Pediatric

Administer as in adults

Interactions

None reported

Contraindications

Documented hypersensitivity; may administer in severe envenomation, despite hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Due to presence of horse serum, agents for emergency treatment of anaphylaxis should be available; premedicate with antihistamines or steroids

Antihistamines

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

Cimetidine (Tagamet)

An H2 antagonist that, when combined with an H1 type, may be useful in treating itching and flushing in anaphylaxis, pruritus, urticaria, and contact dermatitis that do not respond to H1-receptor antagonists alone. Use in addition to H1 antihistamines. Other H2 antagonists are also available.

Dosing

Adult

Patients with persistent symptoms: 300 mg IV followed by PO administration as outpatient q6h for 2 d or for as long as clinically indicated

Pediatric

25-30 mg/kg/d IV in 6 divided doses

Interactions

Can increase blood levels of theophylline, warfarin, tricyclic antidepressants, triamterene, phenytoin, quinidine, propranolol, metronidazole, procainamide, and lidocaine

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Elderly people may experience confusional states; may cause impotence and gynecomastia in young males; may increase levels of many drugs; adjust dose or discontinue treatment if changes in renal function occur

Diphenhydramine (Benadryl, Benylin, Bydramine)

Used for the symptomatic relief of allergic symptoms caused by histamine released in response to allergens.

Dosing

Adult

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

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

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

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

May exacerbate angle-closure glaucoma, hyperthyroidism, peptic ulcer, and urinary tract obstruction

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).

Diphtheria-tetanus toxoid (dT)

Used to induce active immunity against tetanus in selected patients. Tetanus and diphtheria toxoids are the immunizing agents of choice for most adults and children >7 y. Booster doses are necessary to maintain tetanus immunity throughout life because tetanus spores are ubiquitous.
In children and adults, administer into the deltoid or midlateral thigh muscles. In infants, preferred site of administration is the mid thigh laterally

Dosing

Adult

Primary immunization: 0.5 mL IM; administer 2 injections 4-8 wk apart and a third dose 6-12 m after the second injection.
Booster dose: 0.5 mL IM q10y

Pediatric

Administer as in adults

Interactions

Patients receiving immunosuppressants, including corticosteroids or radiation therapy, may remain susceptible despite immunization because of poor immune response; cimetidine may enhance or augment delayed-hypersensitivity responses to skin-test antigens; avoid concurrent use of medication with systemic chloramphenicol because it may impair amnestic response to tetanus toxoid; concurrent use of tetanus immune globulin may delay development of active immunity by several days (interaction is nevertheless clinically insignificant and does not preclude its concurrent use)

Contraindications

Documented hypersensitivity; history of any type of neurological symptoms or signs following administration of this product; FDA recommends that elective tetanus immunization be deferred during any outbreak of poliomyelitis because tetanus toxoid injections are an important cause of provocative poliomyelitis

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Do not use to treat actual tetanus infections or for immediate prophylaxis of unimmunized individuals (use tetanus antitoxin instead, preferably human tetanus immune globulin); diminished antibody response to active immunization may be observed in patients receiving immunosuppressive therapy; better to defer primary diphtheria immunization until immunosuppressive therapy discontinued; routine immunization of symptomatic and asymptomatic persons with HIV is recommended

Immune globulins

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

Tetanus immune globulin (Hyper-Tet)

Used for passive immunization of any person with a wound that might be contaminated with tetanus spores.

Dosing

Adult

Prophylaxis: 250-500 U IM in opposite extremity to tetanus toxoid lesion
Clinical tetanus: 3000-10,000 U IM

Pediatric

Prophylaxis: 250 U IM in opposite extremity as tetanus toxoid
Clinical tetanus: 3000-10,000 U IM

Interactions

None reported

Contraindications

Because antibodies in globulin preparation may interfere with immune response to vaccination, do not administer within 3 mo of live-virus immune globulin administration; may be necessary to revaccinate persons who received immune globulin shortly after live-virus vaccination

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Persons with isolated immunoglobulin A (IgA) deficiency have potential for developing antibodies to IgA and may have anaphylactic reactions to subsequent administration of blood products that contain IgA; do not perform skin testing because intradermal injection of concentrated gamma globulin may cause localized area of inflammation and can be misinterpreted, causing the medication to be withheld from a patient not allergic to this material; true allergic responses to human gamma globulin given in prescribed IM manner are extremely rare; do not admix with other medications because usually incompatible

Benzodiazepines

By increasing the action of GABA (inhibitory neurotransmitter), counteract scorpion-induced excessive motor activity and nervous system excitation.

Lorazepam (Ativan)

Sedative hypnotic with short onset of effects and relatively long half-life.
By increasing action of GABA, which is a major inhibitory neurotransmitter in the brain, may depress all levels of CNS, including limbic and reticular formation.

Dosing

Adult

1-4 mg IV over 2-5 min; may repeat dose in 10-15 min prn

Pediatric

0.05 mg/kg IV over 2-5 min; may repeat dose in 10-15 min prn

Interactions

Toxicity in CNS increases when used concurrently with alcohol, phenothiazines, barbiturates, and MAOIs

Contraindications

Documented hypersensitivity; preexisting CNS depression, hypotension, and narrow-angle glaucoma

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in renal or hepatic impairment, myasthenia gravis, organic brain syndrome, Parkinson disease, hypotension, and respiratory depression

Midazolam (Versed)

Short-acting benzodiazepine that can be administered in continuous infusion for severe nervous system excitation.

Dosing

Adult

0.1 mg/kg IV bolus then 0.1 mg/kg/h; titrate dose upward q5min until symptoms controlled

Pediatric

Administer as in adults

Interactions

Sedative effects may be antagonized by theophyllines; narcotics and erythromycin may accentuate sedative effects because of decreased clearance

Contraindications

Documented hypersensitivity; preexisting hypotension, narrow-angle glaucoma, and sensitivity to propylene glycol (the diluent)

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Caution in congestive heart failure, pulmonary disease, renal impairment, and hepatic failure; may require intubation and pressor support

Barbiturates

Used to counteract scorpion-induced hyperactivity.

Pentobarbital (Nembutal)

Short-acting barbiturate with sedative and anticonvulsant properties used to produce barbiturate coma for severe CNS hyperexcitation. Requires patient intubation prior to use.

Dosing

Adult

12 mg/kg IV bolus, then 5 mg/kg/h; titrate to symptom abatement or EEG inactivity

Pediatric

Administer as in adults

Interactions

Concomitant use with alcohol may produce additive CNS effects and death; chloramphenicol may inhibit metabolism; may enhance chloramphenicol metabolism; MAOIs may enhance sedative effects of barbiturates; valproic acid appears to decrease barbiturate metabolism, increasing toxicity; barbiturates can decrease effects of anticoagulants (patients may require dosage adjustments if barbiturates are added to or withdrawn from regimen); decreased contraceptive effect may occur due to induction of microsomal enzymes (alternate form of birth control is suggested); barbiturates may decrease corticosteroid and digitoxin effects through induction of hepatic microsomal enzymes that increase metabolism; barbiturates decrease theophylline levels and may decrease effects; may decrease verapamil bioavailability

Contraindications

Documented hypersensitivity; liver failure; porphyria

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Patient may become tolerant to hypnotic effects; caution in patients with hypovolemic shock, respiratory dysfunction, hypotension, renal dysfunction, congestive heart failure, previous addiction to sedative hypnotics, and congestive heart failure

Local anesthetics

Tend to be more effective than opiates to control paresthesia and pain at the sting site.

Bupivacaine (Marcaine)

May reduce pain by slowing nerve impulse propagation and reducing action potential, which, in turn, prevents initiation and conduction of nerve impulses.

Dosing

Adult

1.25 mg/kg/dose intralesionally until pain subsides; not to exceed 3-4 mg/kg

Pediatric

Administer as in adults

Interactions

May enhance effects of CNS depressants; coadministration may increase toxicity of MAOIs, TCAs, beta-blockers, vasopressors, and phenothiazines

Contraindications

Documented hypersensitivity; septicemia, spinal deformities, severe hypertension, and existing neurologic disease

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Test a dose and monitor for CNS toxicity, cardiovascular toxicity, and signs of unintended intrathecal administration; caution with inflammation or sepsis in region of proposed injection; monitor patient's state of consciousness after each injection; caution in hypertension, cerebral vascular insufficiency, peripheral vascular disease or heart block, hypoxia, hypovolemia, and arteriosclerotic heart disease

Adrenergic blocking agents and vasodilators

Used to counteract the scorpion-induced adrenergic cardiovascular effect.

Labetalol (Normodyne, Trandate)

Blocks beta1-adrenergic, alpha-adrenergic, and beta2-adrenergic receptor sites, decreasing blood pressure.

Dosing

Adult

20 mg IV then 40 mg IV repeated q10-15min until BP controlled or until the maximum accumulative dose of 300 mg is reached

Pediatric

Not established
Suggested: 0.1 mg/kg IV; repeat q15-20min as last resort

Interactions

Decreases effect of diuretics and increases toxicity of methotrexate, lithium, and salicylates; may diminish reflex tachycardia resulting from nitroglycerin use without interfering with hypotensive effects; cimetidine may increase blood levels; glutethimide may decrease effects by inducing microsomal enzymes

Contraindications

Documented hypersensitivity; cardiogenic shock, pulmonary edema, bradycardia, atrioventricular block, uncompensated congestive heart failure, reactive airway disease, and severe bradycardia

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Caution in impaired hepatic function; discontinue therapy if signs of liver dysfunction occur; in elderly patients, a lower response rate and higher incidence of toxicity may be observed; caution with concomitant beta-blockers; beware of continued hypertension despite decreasing heart rate due to insufficient alpha blockade

Prazosin (Minipress)

Counteracts scorpion-induced adrenergic cardiovascular effects. May improve pulmonary edema through vasodilatory effects.

Dosing

Adult

1 mg PO bid/tid; not to exceed 5 mg/dose

Pediatric

Not established

Interactions

Acute postural hypotensive reaction from beta-blockers may worsen; indomethacin may decrease antihypertensive activity; verapamil may increase serum levels and may increase patient's sensitivity to prazosin-induced postural hypotension; may decrease antihypertensive effects of clonidine

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Caution in renal insufficiency and hypotension

Hydralazine (Apresoline)

Decreases systemic resistance through direct vasodilation of arterioles

Dosing

Adult

10-20 mg IV q4-6h

Pediatric

Not established

Interactions

MAOIs and beta-blockers may increase toxicity

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

May cause hydralazine-induced tachycardia, SLE-type syndrome, and peripheral neuritis

Anticholinergics

Used to counteract scorpion-induced cholinergic symptoms. 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.

Atropine (Atropair)

Used to increase heart rate through vagolytic effects, causing an increase in cardiac output. Also treats bronchorrhea associated with scorpion envenomations. Atropine causes a reversible blockade of muscarinic receptors with subsequent anticholinergic effects. Has been used to reverse vagally induced symptomatic bradycardias, which may be associated with scorpion envenomation. Its use for dry secretions is debated. Will not reverse the somatic or other cranial nerve symptoms.

Dosing

Adult

0.5-1 mg IV q15min until desired effect (Note: for vagolytic cardiac effects, there is a 3-mg limit)

Pediatric

0.01 mg/kg IV q15min until desired effect (Note: For cardiac vagolytic effects, there is a 3-mg limit)

Interactions

Coadministration with other anticholinergics (eg, pramlintide) has additive effects; pharmacologic effects of atenolol and digoxin may increase; antipsychotic effects of phenothiazines may decrease; TCAs with anticholinergic activity may increase effects

Contraindications

Documented hypersensitivity; thyrotoxicosis, narrow-angle glaucoma, and tachycardia

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Avoid in Down syndrome and/or children with brain damage to prevent hyperreactive response; also avoid in patients with coronary heart disease, tachycardia, congestive heart failure, cardiac arrhythmias, and hypertension; cardiac monitoring is mandatory; care must be used to detect marked tachycardia, which may be present with scorpion envenomation; caution in patients with peritonitis, ulcerative colitis, hepatic disease, and hiatal hernia with reflux esophagitis; in patients with prostatic hypertrophy, prostatism may cause dysuria and may require catheterization; monitor patients for anticholinergic effects (eg, hyperthermia, dilated pupils, dry mucous membrane, tachycardia)

Vasopressors/inotropics

Used to combat hypotension refractory to IV fluid therapy.

Norepinephrine (Levophed)

Indicated for persistent hypotension not responsive to judicious fluid loading and sodium bicarbonate.

Dosing

Adult

0.05-0.15 mcg/kg/min IV infusion; titrate to effect

Pediatric

0.1-1 mcg/kg/min IV infusion; titrate to effect

Interactions

Chlorpromazine enhances pressor response by blocking reflex bradycardia caused by norepinephrine

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus

Precautions

Administer into a large vein because extravasation may cause severe tissue necrosis; caution in occlusive vascular disease

Dobutamine (Dobutrex)

Sympathomimetic amine with stronger beta than alpha effects. Increases inotropic state with afterload reduction.

Dosing

Adult

5-20 mcg/kg/min IV continuous infusion, titrate to desired response; not to exceed 40 mcg/kg/min

Pediatric

Administer as in adults

Interactions

Beta-blockers antagonize effects

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals

Precautions

Higher dosages may cause increase in heart rate and exacerbate hypotension

Milrinone (Primacor)

Positive inotropic agent and vasodilator with little chronotropic activity.

Dosing

Adult

50 mcg/kg loading dose IV over 10 min, followed by 0.375-0.75 mcg/kg/min continuous IV infusion

Pediatric

Administer as in adults because has been used in the pediatric ICUs, although safety and efficacy not well established

Interactions

May precipitate if infused in the same IV line as furosemide

Contraindications

Documented hypersensitivity

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Slow or stop infusion in patients showing excessive decreases in blood pressure

Follow-up

Further Inpatient Care

• Inpatient care is dictated by the severity of the envenomation and consists of stabilizing the patient, neutralizing the venom, providing supportive therapies, and preventing complications. 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.  
• Treat all patients with severe systemic symptoms in an intensive care unit (ICU) setting because of the unpredictability of the symptomology, the risks associated with antivenin administration, and the need for airway or blood pressure support.
• Young children do worse than adults. Young children may not recover as quickly as adults after scorpion envenomation and are more likely to require observation.

Further Outpatient Care

• Patients displaying local nonascending reactions to the venom may be discharged after 6 hours of observation, with close follow-up. If the patient was treated with a pressure bandage, the symptoms may be delayed and inpatient observation is warranted.
  • 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.
• If an antivenin is administered, monitor the patient for serum sickness over next the few weeks.
• Inform the patient about the possibility of persistent pain or paresthesia at the sting site.
• Instruct patient regarding progression. Discuss symptoms of delayed serum sickness with patients treated with antivenom.

Inpatient & Outpatient Medications

• Give steroids and antihistamines if serum sickness develops.

Transfer

• Transfer is appropriate if antivenin administration or ICU treatments are not available at the institution where the patient initially presents.

Deterrence/Prevention

• Protective clothing, such as shoes or gloves, may prevent some scorpion envenomations. Check shoes, gloves, clothing, and backpacks for scorpions prior to use.
• Keep yards free of debris, which can serve as a place for scorpions to hide.
• Make sure windows and doors fit tightly to prevent scorpions from entering the house.
• Avoid walking barefoot, especially at night when scorpions are active.
• Use a Wood lamp at night because the cuticle of the Centruroides species is fluorescent under ultraviolet light.
• Methods of biological control of scorpions include introducing chickens, ducks, and owls to the area.
• Methods of chemical control of scorpions include using organophosphates, pyrethrins, and chlorinated hydrocarbons.

Complications

• Dilated cardiomyopathy
• Ankylosis of small joints if the sting occurs at a joint
• Rhabdomyolysis
• Persistent paresthesia
• Antivenin anaphylaxis and serum sickness
• Iatrogenic, high-dose, sedative-hypnotic respiratory arrest
• Respiratory arrest
• Cardiac arrest
• Shock
• Seizures
• Rhabdomyolysis
• Death
• Defibrination after M 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.
• Symptoms generally persist for 10-48 hours. If the victim survives the first few hours without severe cardiorespiratory or neurologic symptoms, the prognosis is usually good. Furthermore, surviving the first 24 hours after a scorpion sting also carries a good prognosis.
• A worse prognosis can be expected with the presence of systemic symptoms such as cardiovascular collapse, respiratory failure, seizures, and coma.

Patient Education

• Educate all patients about methods to avoid scorpions (see Deterrence/Prevention).

Miscellaneous

Medicolegal Pitfalls

• Failure to stabilize the airway and vital signs prior to any specific intervention against the venom
• Failure to adequately treat the patient because of underestimation of the envenomation effects
• Failure to admit the patient for systemic symptoms
• Failure to use ICU monitoring for patients who are severely envenomated
• Failure to warn the patient of potential complications and to arrange a follow-up evaluation
• Failure to obtain informed consent before antivenin administration
• Heavy combination use of barbiturates and narcotics for the hyperdynamic state, leading to concurrent respiratory arrest, especially in pediatric patients
  • 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.
• 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.
• Atropine has been used to decrease respiratory secretions but, dangerously, may potentiate the sympathetic overdrive symptoms. However, it should be used in symptomatic bradycardia.

Multimedia

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

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.

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.

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Keywords

scorpion sting, scorpion envenomation, scorpion venom, arthropod sting, insect sting, arachnid sting, venom, antivenom, antivenin, Buthidae, Scorpionidae, Ischnuridae, Buthus, Parabuthus, Mesobuthus, Tityus, Leiurus, Androctonus, Centruroides, Centruroides exilicauda, Centruroides sculpturatus, C sculpturatus, neurotoxin, cardiotoxin, nephrotoxin, toxin, wildlife emergency, envenomation, severe local skin reaction, neurologic collapse, respiratory collapse, cardiovascular collapse, respiratory failure, cardiovascular failure, Buthus, Mesobuthus, Buthotus, Buthus tamulus, Hottentotta, Leiurus, Leiurus quinquestriatus, Leiurus quinquestriatus, Androctonus, Androctonus australis, Hemiscorpius, Hemiscorpius lepturus

Contributor Information and Disclosures

Author

David Cheng, MD, Assistant Professor of Emergency Medicine, Associate Emergency Medicine Residency Director, Associate Medical Director of Emergency Services, University of Arkansas Medical Sciences
David Cheng, MD is a member of the following medical societies: American College of Emergency Physicians, American Heart Association, Council of Emergency Medicine Residency Directors, International Society for Mountain Medicine, National Association of EMS Physicians, Society for Academic Emergency Medicine, Society of Critical Care Medicine, and Wilderness Medical Society
Disclosure: Nothing to disclose.

Coauthor(s)

Judith A Dattaro, MD, FACEP, Assistant Professor of Emergency Medicine in Surgery, Cornell University Medical College; Consulting Staff, Department of Emergency Medicine, Weill-Cornell University Medical Center, New York Presbyterian Hospital
Judith A Dattaro, MD, FACEP is a member of the following medical societies: American Association of Women Emergency Physicians, American College of Emergency Physicians, American Medical Association, Chicago Medical Society, Illinois State Medical Society, and Society for Academic Emergency Medicine
Disclosure: Nothing to disclose.

Ramy Yakobi, MD, MBA, Medical Director of Emergency Department, Beth Israel/Kings Highway Division; Lecturer, Physician Assistant School, Cornell School of Medicine; Lecturer, Pre-hospital Management of Patient, Cornell/New York Presbyterian Hospital; Director of Emergency Department, New York Community Hospital
Ramy Yakobi, MD, MBA is a member of the following medical societies: American Academy of Emergency Medicine and American College of Emergency Physicians
Disclosure: Nothing to disclose.

Medical Editor

Lisa Kirkland, MD, FACP, CNSP, MSHA, Assistant Professor, Department of Internal Medicine, Division of Hospital Medicine, Mayo Clinic; ANW Intensivists, Abbott Northwestern Hospital
Lisa Kirkland, MD, FACP, CNSP, MSHA is a member of the following medical societies: American College of Physicians, Society of Critical Care Medicine, and Society of Hospital Medicine
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Om Prakash Sharma, MD, FRCP, FCCP, DTM&H, Professor, Department of Medicine, Division of Pulmonary and Critical Care Medicine, University of Southern California Keck School of Medicine
Om Prakash Sharma, MD, FRCP, FCCP, DTM&H is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American College of Chest Physicians, American College of Physicians, American Federation for Medical Research, American Osler Society, American Thoracic Society, New York Academy of Medicine, and Royal Society of Medicine
Disclosure: Keck School of Medicine, USC None None

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Timothy D Rice, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Physicians
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Jonathan Adler, MD, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital; Division of Emergency Medicine, Harvard Medical School
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