Scorpion Toxicity

Article Author:
Zafar Shamoon
Article Author (Archived):
Ryan Peterfy
Article Editor:
Babak Khazaeni
Updated:
7/31/2019 9:58:50 AM
PubMed Link:
Scorpion Toxicity

Introduction

Scorpions are a common arthropod found all over the world, including every continent except Antartica. If threatened, a scorpion may use its long, flexible tail to sting a potential predator. Frequently, people unknowingly come into contact with these species and experience the painful sensation of envenomation. When a victim of a scorpion sting presents to the emergency department, there are a few things to keep in mind to safely disposition the patient.[1][2][3][4]

Etiology

While there are thought to be about 1750 species of scorpions in the world, only 25 are considered to be lethal to humans. In most cases, the sting of a scorpion causes pain but is relatively harmless to a healthy adult. Species found in Asia, Africa, and South America may need medical attention due to the potential toxic effects of their venom. Rather than just causing a local skin reaction, these species are capable of producing systemic symptoms including hemolysis, hemorrhage, and neuromuscular dysfunction. Scorpions may sting many times, but their venom is depleted with each sting.

Epidemiology

The effect of the scorpion sting is highly dependent on the species. While species like Centruroides and Parabuthus cause neuromuscular issues, Buthus, Mesobuthus, and Androctonus exhibit life-threatening cardiovascular effects. These worrisome effects are mostly seen in the elderly and even more so in infants and young children.

Pathophysiology

In Mexico and the United States, many scorpion stings occur each year; however, only a few cause systemic effects. When serious symptoms do occur, they are usually due to the Centruroides species. Because of this, a classification scale has been created to grade each envenomation by a Centruroides scorpion.[5][6][7]

Grade 1: Local pain and paresthesias at the sting site. The puncture wound may not be noticeable in this grade. The "tap test" may confirm a provider's suspicion by distracting the patient and tapping on the area of the sting, causing increased pain. This does not occur with other species. Care is limited to analgesia.

Grade 2: Local pain and paresthesias at the sting site as well as proximally. Recommended care again includes analgesia with optional anxiolytics if needed.

Grade 3: Grade 2 with added cranial nerve (increased oral secretions, blurry vision, rapid tongue movement, nystagmus) or skeletal neuromuscular dysfunction (flailing of the extremities and tetanus-like arching of the back). These patients require analgesia and anxiolytics as well as antivenom.

Grade 4: Unlike grade 3 envenomations where the patient will experience either cranial nerve or skeletal muscle dysfunction, grade 4 envenomations include both. This can cause hyperthermia, rhabdomyolysis, pulmonary edema, and multiple organ failures. Again, antivenom is critical in this situation.

Toxicokinetics

Although less than 10% of scorpion stings cause systemic symptoms, those that do can be serious. Neurotoxins are the mainstay of symptomatology in envenomations. The venom of some species can cause prolonged depolarization by causing incomplete inactivation of sodium channels resulting in a slow influx of sodium. This then leads to membrane hyperexcitability and unregulated axon firing.

History and Physical

Most scorpion stings cause a local inflammatory reaction and pain. When the venom affects the sodium channels, this may manifest as seizure-like activity in the patient and obscure the clinical picture, especially when the child or infant is unable to relay an accurate history. Intubation may be required in these patients, as motor hyperactivity of the pharyngeal muscles and uncontrolled diaphragmatic and intercostal neuromuscular activity may be seen. These symptoms may progress quickly, causing impending airway collapse. In the select species causing cardiopulmonary effects, tachycardia, pulmonary edema, and more importantly, cardiogenic shock may be seen. While uncommon, local tissue necrosis days to weeks after the initial sting has also been documented.

Evaluation

History and physical most commonly diagnose scorpion stings. Usually, the patient can visualize the scorpion, and the practitioner will observe an erythematous area on the skin with local inflammation. Numbness and weakness at the site may also be seen. If concern for systemic organ involvement, basic laboratory studies are recommended, including a complete blood count, a comprehensive metabolic panel, PT/INR, PTT, and lipase. Laboratory studies are usually reserved for patients with severe (grade 3 to 4) envenomations. Scorpion stings are known to be an uncommon but real cause of pancreatitis.[8][9][10]

Treatment / Management

Most stings only require supportive therapy including ibuprofen, cleaning of the sting area, and tetanus prophylaxis. Patients should be observed for at least 4 hours, but the onset of life-threatening symptoms occurs much quicker in children, with an average of 14 minutes. In patients with severe envenomation displaying symptoms such as hypersalivation, clonus, rapid eye movements, or restlessness, immediate intervention is critical. These patients may need endotracheal intubation due to the possibility of rapid onset of severe pulmonary edema. As cardiogenic shock can complicate this, administration of dobutamine has been shown to be helpful. Intravenous benzodiazepines may be used if the patient displays muscle spasticity. Antivenom is reserved for patients displaying skeletal muscle or cranial nerve dysfunction who are stung by Centruroides scorpions. It is available in the United States, under the name Anascorp, which is intravenous scorpion-specific F(ab’)2 equine antivenom. It has been shown to reduce the duration of clinical symptoms if given within 4 hours of the sting. The recommended dose is three vials, followed by an additional two if symptoms continue. Complications are low and comprise mostly serum sickness (0.5%). Anascorp is considered much safer than the previous antivenom, which was marketed in 1965 and taken off shelves in 2001 due to its high rates of anaphylaxis (3.4%). No cases of anaphylaxis have been reported in patients administered Anascorp. Although effective, Anascorp can be quite expensive, with some hospitals charging upward of $40,000 per vial. If a patient is observed for 4 hours and is determined to have a mild sting, is tolerating oral intake, and has adequate pain control, the patient may be safely discharged home with return precautions.

Enhancing Healthcare Team Outcomes

Scorpion stings are best managed by a multidisciplnary team that includes poison control center and emergency room nurses. Most patients only require supportive treatment with pain control. In rare cases, the patient may need longer observation in the ICU.  When a grade 3 or 4 envenomation is suspected, the provider should always contact the closest poison control center for assistance and further recommendations. Although most scorpion stings are mild and not life-threatening, scorpion stings can cause significant harm to the patient, especially in very young or elderly patients. In these patients, securing the airway is critical if they are unresponsive to antivenom and other medical interventions as mentioned above.



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