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A review of the diagnosis and treatment of envenomations of scorpions.
This article will review the diagnosis and treatment of envenomations of scorpions. Whether an individual clinician will commonly treat scorpion envenomations depends on where they are practicing. In the United States, anti-venom for scorpion envenomations has helped reduce morbidity and mortality.
Poison control centers in the United States receive close to 17,000 reports of scorpion envenomations per year. There are over 1,700 scorpion species around the world but only 25 are lethal to humans. In the United States there are a number of different species but there are two that cause most significant envenomations. The most common is Centruroides sculpturatus, followed by Centruroides vittatus.
There has been some taxonomic confusion in the past with Centruroides sculpturatus and Centruroides exilicauda being considered the same species and the names used interchangeably in the literature. However, research has concluded they are two separate species. The Centruroides sculpturatus is also known as a bark scorpion for its ability to climb and can be found in trees, rock walls or house walls as well as under rocks or in crevices. The Centruroides vittatus is also known as the striped bark scorpion due to the marking on its back. Both species are found in Arizona, New Mexico, Texas, California, Utah, Nevada, and in adjacent areas of Mexico.[31.32] The Centruroides exilicauda is found in Mexico and is also known as the Baja California scorpion. Its venom is much less toxic to humans than the other two species.
An adult scorpion is typically two to three inches long, with a stinger on its tail which it uses to paralyze prey to make it easier to eat. It also will sting predators(and humans) when threatened. Infants and children are more sensitive to the neurotoxin than adults. Adults are stung more often than children, however children more frequently suffer from severe illness. Scorpion's venom is composed of multiple neurotoxins, an ACE inhibitor, and a component that inhibits platelet aggregation. The neurotoxins inhibit sodium channels of the peripheral nervous system, causing a prolonged membrane action potential and allowing repetitive axonal firing. Symptom onset is typically within a few minutes after the sting and progresses to its maximal effect within five hours. Patients with only localized symptoms can be safely discharged home if there is no progression of the disease after observation for those five hours. There have been no reported deaths from scorpion envenomation in Arizona since 2013.
A grading system has been developed to categorize and assist in the treatment of scorpion stings.
Grade I envenomation causes local pain and paresthesias at the sting site. The puncture wound may not be visible. The sting does not usually produce a local inflammatory reaction, making diagnosis in young children and infants difficult. The "tap test" may confirm a provider's suspicion of a sting by sculpturatus by tapping on the area of the sting, causing increased pain. This may not occur with other scorpion species. Supportive care and analgesia are all that is typically required.
Grade II envenomation causes local pain and paresthesias at the site of the sting as well as proximal to the sting site. Occasionally there may be radiation to contralateral extremities. Care includes analgesia and possibly anxiolytics if needed.
Grade III includes Grade II symptoms with added cranial nerve and bulbar dysfunction (increased oral secretions, blurry vision, rapid tongue movement, nystagmus), or skeletal neuromuscular dysfunction with flailing of the extremities, opisthotonos (tetanus-like hyperextension of the head with arching of the back), or emprosthotonus (forward flexion of the head and feet toward each other) being possible. Autonomic dysfunction may also occur and most commonly symptoms include salivation, vomiting, bronchoconstriction, diaphoresis, and tachycardia. Grade III envenomations can sometimes adversely affect a patient’s airway. In pediatric patients common findings are restlessness, writhing, opsoclonus (uncontrolled chaotic rapid eye movements), tachycardia, and hypersalivation. Patients with Grade III stings generally require analgesia and anxiolytics as well as antivenom.
Grade IV envenomations includes both cranial nerve and skeletal muscle dysfunction, which can lead to hyperthermia, rhabdomyolysis, pulmonary edema, and multiple organ failure. Antivenom will be required.
Grades I and II envenomations generally just require supportive care, ice packs, tetanus immunization if needed, analgesia and possibly anxiolytics.[29,32]
For Grades III or IV envenomation antivenom and hospital admission may be required. In 2011 Anascorp Centruroides (scorpion) immune F(AB)2 was approved by the FDA, which contains purified fragments of immunoglobulin G that bind and neutralize venom. A typical dose is three to five vials. It is made from horse serum so serum sickness, allergic reactions, and anaphylaxis may occur. Without antivenom, the average time to resolution of symptoms is approximately 30 hours. In one small study of 15 critically ill children, 100% of the antivenom treated patients had resolution of symptoms within four hours versus 14% in the placebo group. Typically, about 2% of all scorpion envenomated patients will require antivenom.
Fortunately, most of the envenomations from scorpions are not severe. However, severe systemic toxicity can occur. Deaths are rare, especially with the availability of anti-venom for scorpion envenomations. Antihistamines may help with itching and there is one anecdotal case series, not confirmed by other studies, where the author suggested that antihistamines may help with wound healing.
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