Tox Talks: Arizona Bark Scorpion

Phoenix is a transplant city, to be sure. Plenty of Californians, Midwesterners, and folks from all over have made their way to our city one way or another and have had to acclimate themselves to the many unique features of the Valley of the Sun. In my experience, the topic that concerns new residents more than any other isn’t the heat, but scorpions. It’s quite understandable as not many US states have venomous animals, and their claws and stinging tails certainly make them intimidating creatures. Or maybe a lot of people have lingering fears from the awful CGI of the Scorpion King from The Mummy Returns. (Seriously, who’s responsible for making Dwayne Johnson look like this: https://www.youtube.com/watch?v=RYHaarxQTFk&ab_channel=Movieclips ?) Regardless, we as future physicians should be aware of the health hazards of scorpion envenomation and be able to recognize the potentially fatal complications, especially here in the Grand Canyon State.

The most common scorpion in Arizona is, fittingly, the Arizona bark scorpion Centruroides sculpturatus.¹ This species can also be found in Texas, Nevada, California, Oklahoma, and New Mexico.² They are nocturnal creatures that generally do not attack humans unless provoked, but there are still over 10,000 reports per year of envenomations in Arizona alone, with the vast majority of envenomations occurring in residences. One unique characteristic of scorpions is that they fluoresce under a black light (likely due to the presence of riboflavin), which can make them easily spotted in the dark. Female bark scorpions are larger than males, and there is some evidence to suggest that the smaller males may have more potent venom.³

The chemical makeup of bark scorpion venom is quite complex, but the most medically pertinent component is a heat-stable and protease-resistant neurotoxin.¹ This toxin alters axonal sodium channels, leading to more rapid and sustained action potentials which cause a variety of symptoms. Increased presynaptic activity at the neuromuscular junction leads to spontaneous and uncoordinated muscle movement, increased parasympathetic activity leads to increased salivation, and increased catecholamine release leads to autonomic dysfunction. The big picture is that everything is amped up by the increased neurotransmission.

Most commonly patients complain of pain and paresthesia around the site of the sting which can move proximally up the affected limb.^4,5 More severe cases feature one or more of: motor hyperactivity, cranial nerve abnormalities, or autonomic instability. Patients may have restlessness, flailing of the extremities, or tetanus-like spasms. Cranial nerve abnormalities include opsoclonus (characteristically roving, multidirectional eye movements), blurred vision, tongue fasciculations, drooling, and occasionally stridor and respiratory arrest. Additionally, patients are often tachycardic and hypertensive, and younger patients especially may present with vomiting. Children and elderly patients develop severe symptoms more commonly than adults, despite adults being stung significantly more often. Another thing to note – the striped bark scorpion Centruroides vittatus is the more common species in states throughout the southwestern and southeastern US other than Arizona, but its envenomation is characterized more by a hypersensitivity reaction and is generally not as dangerous as C. sculpturatus.⁶

Diagnosis is largely clinical based on history and physical exam, but for severe envenomations consider obtaining serum electrolytes, liver enzymes (AST & ALT), BUN, creatinine, serum creatine kinase, and urinalysis. Rhabdomyolysis may result from muscular hyperactivity, which could be observed in those labs.

Like many envenomations, treatment is primarily supportive. Pain can be controlled with NSAIDs or opioids depending on the severity, and patients with mild cases may only require wound cleaning, fluids, and observation for at least 4 hours. However, if the patient is young or elderly, or presents with any concerning symptoms the first step should be to call poison control (800-222-1222). They can assist in guiding the next steps of care, which may include benzodiazepines or antivenom. Of course, the ABC’s always apply: if the patient has excessive secretions or cannot protect their airway, steps such as suctioning or intubation may be necessary.

Speaking of that antivenom — an FDA-approved Centruroides scorpion-specific F(ab’)2 equine antivenom has been available in Arizona since 2011; the brand name is Anascorp. Patients who receive the antivenom can see resolution of symptoms within 4 hours and may see an overall reduction in ICU admission and hospital stays.⁷ Interestingly, benzodiazepines (especially long-acting ones) may interfere with the function of the antivenom, so it’s definitely prudent to call the poison control center when formulating your treatment plan. One more thing to keep in mind: drugs.com currently lists Anascorp as $4,489.34 per vial, and 3-5 vials are usually recommended for treatment.⁸

There’s one more interesting topic I wanted to discuss that actually prompted the writing of this entire article. If you use Anki, odds are you’ve come across, rolled your eyes, and possibly chuckled at the mnemonic listing the causes of acute pancreatitis – I GET PP SMASHED. One of the causes always left me with more questions though: scorpion sting. After all, there are plenty of scorpions in our home state. Are we at risk for acute pancreatitis? The short answer is no. Well, not unless you have any trips to Trinidad and Tobago planned. 

Turns out the scorpions that most commonly cause pancreatitis belong to the genus Tityus, which has over 220 species that range from Central America and the Caribbean to South America. Tityus trinitatis in Trinidad and Tityus stigmurus in Brazil in particular seem to come up frequently in case reports of acute pancreatitis after envenomations.^9,10 These scorpions in general are more dangerous than those found in the US, and their stings can cause other organ dysfunction as well, with a higher fatality rate. 

While scorpions are still not the nicest thing to look at, the medicine behind scorpion envenomations is fascinating and we should be knowledgeable about the critters that also call our state home. If you take a blacklight outside on a cool Arizona night, who knows, maybe you’ll find The Rock. I mean a scorpion. Under a rock.

John Michael Sherman

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John Michael Sherman is a member of the UA College of Medicine - Phoenix Class of 2023. Born in Chicago, IL, he's been an Arizona resident for 15 years but is still heat-intolerant. He received a degree in Jazz Trumpet Performance from ASU and was a professional freelance musician for several years before starting medical school. He enjoys exploring new recipes in the kitchen, swing dancing with his wife, and (for some reason) riding his bike for long distances.

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