Scorpion envenomation is caused by stings from scorpions, most commonly on the extremities. In the United States, Centruroides sculpturatus (bark scorpion) is the only species associated with severe systemic envenomation. [1-2] Up to 95% of stings result in local symptoms only; severe systemic envenomation occurs in <5% of cases and is far more common in children. [1][3] The pathophysiology centers on ion-channel toxins that trigger massive catecholamine release and simultaneous sympathetic/parasympathetic excitation. [3-4]
The following figure illustrates the pathophysiological cascade from venom toxins through autonomic excitation to cardiovascular collapse and respiratory failure:
1. History
- Circumstances of sting: Location (geographic region, indoor vs. outdoor), time of day (most stings are nocturnal), activity at time of sting (reaching into shoes, crevices, woodpiles) [1][5]
- Symptom characterization: Immediate sharp pain at sting site, paresthesias (tingling, numbness), "tap test" — tapping the sting site reproduces severe pain [1][4]
- Timing and progression: Onset of local pain is immediate; systemic symptoms typically develop within 30 minutes to 4 hours [2]
- Associated symptoms: Agitation, restlessness, drooling, difficulty swallowing, slurred speech, visual changes, muscle twitching, vomiting [2][4]
- Important negatives: Absence of dysphagia, respiratory distress, abnormal eye movements, and muscle spasms helps exclude severe envenomation [1]
2. Alarm Features
- Roving/abnormal eye movements (opsoclonus) — hallmark of severe Centruroides envenomation [2]
- Loss of muscle control, uncoordinated neuromotor hyperactivity [2][6]
- Respiratory distress: Excessive secretions, airway obstruction, aberrant ventilatory effort [2]
- Hypersalivation, frothing at the mouth, dysphagia [6]
- Severe hypertension or hypotension/shock [1][4]
- Pulmonary edema (cardiogenic or noncardiogenic) [1][3]
- Seizures, altered mental status (especially in young children) [5]
- Skin mottling/marbling — independent predictor of mortality in children [5]
3. Medications
Treatments by grade
- Grade 1 (local): Oral acetaminophen, NSAIDs, opioids; topical 5% lidocaine; ice application [1][7]
- Grade 2 (systemic, mild): Parenteral analgesia; benzodiazepines (midazolam preferred) for agitation/muscle spasm; consider prazosin for hypertension [1]
- Grade 3–4 (severe): Anascorp (centruroides immune F(ab')₂) — initial dose 3 vials IV over 10 min, additional 1 vial q30–60 min as needed; IV fentanyl for analgesia; IV benzodiazepines; dobutamine for cardiogenic shock; nitroglycerin for pulmonary edema [1][4][6]
Cautions
- Anascorp is equine-derived — risk of anaphylaxis (0.2% acute reactions) and serum sickness (0.5%). Have epinephrine, corticosteroids, and diphenhydramine at bedside [6][8]
- Use benzodiazepines with caution when administering antivenom (may mask progression) [1]
- Avoid beta-blockers in autonomic storm (may worsen unopposed alpha stimulation) [4]
4. Diet
- NPO if any concern for airway compromise, excessive secretions, or potential need for intubation
- Maintain hydration — vomiting and diaphoresis can cause dehydration, especially in children
- No specific long-term dietary considerations
5. Review of Systems
- Neurologic: Paresthesias (local and remote), muscle spasms, visual changes, difficulty speaking/swallowing, seizures
- Cardiovascular: Palpitations, chest pain, dyspnea on exertion
- Respiratory: Shortness of breath, cough, excessive secretions, choking sensation
- GI: Nausea, vomiting, diarrhea, abdominal pain (pancreatitis can occur) [1]
- Autonomic: Diaphoresis, lacrimation, salivation, urinary incontinence, priapism [4]
- Constitutional: Fever, agitation, restlessness
6. Collateral History and Family History
- Collateral: Witnesses can describe the scorpion (size, color — bark scorpions are small, tan/yellow); confirm time of sting; describe progression of symptoms
- Prior stings: Previous antivenom exposure increases risk of hypersensitivity to Anascorp [6]
- Allergies: History of equine protein allergy is a relative contraindication to antivenom [6]
- Family history is generally not relevant unless there is a hereditary condition affecting autonomic function or cardiac conduction
7. Risk Factors
- Age <5 years — strongest risk factor for severe envenomation and mortality (lower body mass → higher venom-to-volume ratio) [1-2][9]
- Geographic location: Southwestern US (Arizona most common), Mexico, Middle East, North Africa, India, Brazil [3][10]
- Rural setting and delayed time-to-treatment (>2–3 hours) [5][9]
- Nocturnal stings (78% of pediatric stings in one series) [5]
- Species: Centruroides (New World), Androctonus, Leiurus, Mesobuthus (Old World) [4][10]
- Outdoor activities: Camping, hiking, working in construction or agriculture
8. Differential Diagnosis
- Black widow spider bite: Severe crampy pain, muscle rigidity, diaphoresis, hypertension — but no opsoclonus or cranial nerve findings; latrodectism has a more diffuse muscle cramping pattern [7]
- Anaphylaxis: Urticaria, angioedema, bronchospasm, hypotension — lacks neuromuscular excitation
- Organophosphate poisoning: Cholinergic toxidrome (SLUDGE) — but typically has miosis and bradycardia without the mixed sympathetic/parasympathetic picture
- Tetanus: Muscle rigidity and spasms — but trismus is characteristic and there is no sting history
- Strychnine poisoning: Opisthotonus, muscle spasms — but no autonomic storm
- Serotonin syndrome: Agitation, clonus, hyperthermia — medication history distinguishes
- Other arthropod envenomation: Hymenoptera (bee/wasp) — primarily allergic; brown recluse — local necrosis pattern
9. Past Medical History
- Prior scorpion stings and antivenom use (sensitization risk) [6]
- Cardiac disease — pre-existing cardiomyopathy increases vulnerability to catecholamine surge [3]
- Asthma/reactive airway disease — increased risk from respiratory secretions and bronchospasm
- Immunocompromised states — may affect wound healing
- Tetanus immunization status — update if not current [1]
10. Physical Exam
Vital signs
- Tachycardia, hypertension (early sympathetic phase); hypotension (late/severe — suggests cardiogenic shock) [4]
- Tachypnea, hypoxia (pulmonary edema or secretion-related obstruction)
- Hyperthermia [4]
Focused exam
- Sting site: Often difficult to visualize; local erythema, edema, fasciculations; positive "tap test" (exquisite pain on tapping) [1][4]
- Eyes: Roving eye movements, opsoclonus, nystagmus — pathognomonic for severe Centruroides envenomation [2][11]
- Oropharynx: Hypersalivation, frothing, tongue fasciculations, stridor [2][6]
- Neurologic: Uncoordinated limb movements, muscle spasms, hyperreflexia, dysarthria, ataxia [2]
- Cardiovascular: Irregular rhythm, S3 gallop (if cardiomyopathy), crackles (pulmonary edema) [4]
- Skin: Diaphoresis, piloerection, mottling (poor prognostic sign in children) [5]
11. Lab Studies
Grade 1 (local only): No labs required [4]
Grade 2–3 (systemic)
- BMP — electrolytes (hypokalemia common and correlates with severity), renal function [1][12]
- CBC — leukocytosis
- Troponin and BNP — cardiac biomarkers for myocarditis/cardiomyopathy [1][13]
- Lipase — pancreatitis is a recognized complication [1][4]
- LFTs — hepatic involvement
- CK — rhabdomyolysis [1]
- Coagulation studies (PT/INR, fibrinogen) — coagulopathy with certain Old World species [1][10]
- Urinalysis — myoglobinuria [1]
- Lactate, VBG — assess perfusion in shock
12. Imaging
- Chest X-ray: Indicated if respiratory distress, hypoxia, or suspected pulmonary edema [1]
- Echocardiography: Gold standard for assessing Takotsubo-like cardiomyopathy in severe envenomation; assess LV function, wall motion abnormalities [3-4][13]
- CT head: Only if concern for alternative diagnosis (seizures, altered mental status without clear envenomation history)
- Imaging is unnecessary for isolated Grade 1 stings
13. Special Tests
- "Tap test": Tapping the sting site reproduces severe pain — supports diagnosis of scorpion sting
- Bedside echocardiography (POCUS): Rapid assessment of cardiac function in hemodynamically unstable patients [4]
- Envenomation grading scale: Use the 3- or 4-tier grading system to guide management [1][4]
14. ECG
- Indications: All patients with Grade 2+ envenomation; any hemodynamic instability [1][4]
- Common findings: Sinus tachycardia (82% of myocarditis cases), ST-T wave changes (64.6%), T-wave inversions [4][13]
- QT prolongation — correlates with hypokalemia and severity [12]
- Other: Atrial tachycardia, ventricular extrasystoles, bundle-branch block [4]
- Dangerous patterns: ST elevation mimicking STEMI (catecholamine-induced myocardial ischemia), ventricular tachycardia/fibrillation [4][14]
15. Assessment
- >95% of stings are mild (Grade 1) and self-limited [1][3]
- Severe envenomation (<5%) is a medical emergency driven by massive catecholamine release causing a mixed autonomic excitation syndrome with simultaneous sympathetic and parasympathetic effects [3-4]
- Cardiovascular complications (Takotsubo-like cardiomyopathy, pulmonary edema, cardiogenic shock) are the primary cause of mortality, particularly with Old World species [3][13]
- Neuromuscular toxicity (opsoclonus, respiratory failure from secretions/muscle dysfunction) predominates with Centruroides species [2]
- Atypical presentations: Pancreatitis, coagulopathy (Hemiscorpius species), rhabdomyolysis, acute kidney injury [1][10]
- Mortality in confirmed scorpion-related myocarditis is approximately 7.3%; independent predictors of mortality in children include diarrhea, skin marbling, respiratory distress, and GCS 3–9 [5][13]
16. Treatment Plan
Initial stabilization (all grades)
- ABCs — assess airway for secretions, stridor
- IV access, continuous monitoring, pulse oximetry
- Local wound care, tetanus prophylaxis [1]
Grade 1
- Oral analgesia (acetaminophen, ibuprofen, opioids PRN)
- Topical 5% lidocaine or ice for local pain [7]
- Observe minimum 4 hours [1]
Grade 2
- IV midazolam 0.05–0.1 mg/kg for agitation/muscle spasm
- Parenteral analgesia (IV fentanyl 1–2 mcg/kg)
- Consider prazosin for hypertension [1]
- Contact Poison Control: 1-800-222-1222 [1]
Grade 3–4
- Anascorp: 3 vials reconstituted in NS, diluted to 50 mL, infused IV over 10 min. Additional 1 vial q30–60 min as needed until symptoms resolve [6]
- Same dose for adults and children [6]
- Mean time to symptom resolution: ~1.4 hours (pediatric ~1.3 hrs, adult ~1.9 hrs) [6]
- 100% symptom resolution within 4 hours in the pivotal RCT vs. 14.3% with placebo [6]
- IV midazolam for neuromuscular hyperactivity
- Dobutamine for cardiogenic shock [1][4]
- Nitroglycerin or prazosin for pulmonary edema/refractory hypertension [1]
- Intubation and mechanical ventilation if airway compromise [1]
- Correct hypokalemia aggressively [12]
17. Disposition
- Discharge (Grade 1): After minimum 4 hours of observation with no progression of symptoms and adequate pain control on oral medications [1]
- Observation/admission (Grade 2): Until symptoms are improving and controlled on oral agents; consider 12–24 hour observation [1]
- ICU admission (Grade 3–4): Neuromuscular dysfunction, cranial nerve findings, hemodynamic instability, respiratory compromise, or need for antivenom [1]
- Specialist consultation triggers:
- Poison Control for all Grade 2+ [1]
- Toxicology for antivenom decisions
- Cardiology if echocardiographic abnormalities or troponin elevation
- Pediatric ICU for all children with systemic symptoms [2]
18. Follow Up / Return Precautions
- Follow-up: Within 1–2 weeks after antivenom administration to monitor for delayed serum sickness (rash, fever, myalgia, arthralgia — occurs in ~0.5% of Anascorp recipients) [6]
- Return immediately for: Recurrence of muscle spasms, difficulty breathing, difficulty swallowing, excessive drooling, abnormal eye movements, chest pain, or any new neurologic symptoms
- Expected recovery: Grade 1 stings resolve within hours to days. Severe envenomation treated with antivenom typically resolves within 1–4 hours. Takotsubo-like cardiomyopathy is reversible over days to weeks [3][6]
- Patient counseling: Shake out shoes and clothing before wearing in endemic areas; use UV flashlights at night (scorpions fluoresce); seal cracks in homes; wear gloves when moving rocks/wood [1]
References
1. Arthropod Bites and Stings. — Herness J, Snyder MJ, Newman RS. American Family Physician. 2022.
2. Antivenom for Critically Ill Children with Neurotoxicity from Scorpion Stings. — Boyer LV, Theodorou AA, Berg RA, et al. The New England Journal of Medicine. 2009.
3. Scorpion Envenomation: State of the Art. — Abroug F, Ouanes-Besbes L, Tilouche N, Elatrous S. Intensive Care Medicine. 2020.
4. Scorpion Envenomation. — Isbister GK, Bawaskar HS. The New England Journal of Medicine. 2014.
5. Clinical Features and Prognosis of Severe Scorpion Envenomation in Children. — Rebahi H, Ba-M'hamed S, Still ME, et al. Pediatrics International : Official Journal of the Japan Pediatric Society. 2022.
6. FDA Drug Label. — Updated date: 2013-12-04. Food and Drug Administration.
7. 2024 American Heart Association and American Red Cross Guidelines for First Aid. — Hewett Brumberg EK, Douma MJ, Alibertis K, et al. Circulation. 2024.
8. Safety of Intravenous Equine F(ab')2: Insights Following Clinical Trials Involving 1534 Recipients of Scorpion Antivenom. — Boyer L, Degan J, Ruha AM, et al. Toxicon : Official Journal of the International Society on Toxinology. 2013.
9. Risk Factors for Fatal Scorpion Envenoming Among Brazilian Children: A Case-Control Study. — Almeida ACC, Carvalho FM, Mise YF. Transactions of the Royal Society of Tropical Medicine and Hygiene. 2021.
10. Scorpions and Scorpion Sting Envenoming (Scorpionism) in the Arab Countries of the Middle East. — Amr ZS, Abu Baker MA, Al-Saraireh M, Warrell DA. Toxicon : Official Journal of the International Society on Toxinology. 2021.
11. Scorpion Stings and Antivenom Use in Arizona. — Klotz SA, Yates S, Smith SL, et al. The American Journal of Medicine. 2021.
12. Serum Level of Scorpion Toxins, Electrolytes and Electrocardiogram Alterations in Mexican Children Envenomed by Scorpion Sting. — Osnaya-Romero N, Acosta-Saavedra LC, Goytia-Acevedo R, et al. Toxicon : Official Journal of the International Society on Toxinology. 2016.
13. Scorpion Envenomation-Associated Myocarditis: A Systematic Review. — Fereidooni R, Shirzadi S, Ayatizadeh SH, et al. PLoS Neglected Tropical Diseases. 2023.
14. Myocardial Ischemia After Severe Scorpion Envenomation: A Narrative Review. — Bahloul M, Bouchaala K, Chtara K, Kharrat S, Bouaziz M. The American Journal of Tropical Medicine and Hygiene. 2024.