Scorpion Envenomation

Scorpion stings number about 1.2 million a year worldwide, with about 3000 deaths, mostly in children in tropical and subtropical regions. Only about 25 species in the family Buthidae are dangerous: Centruroides (Mexico and southwestern North America), Androctonus, Leiurus and Buthus (North Africa and the Middle East), Mesobuthus tamulus (the Indian red scorpion), Tityus (South America) and Parabuthus and Hottentotta (eastern and southern Africa).

Neurotoxic venom peptides prolong sodium channel opening and block potassium channels, causing release of acetylcholine, norepinephrine and epinephrine (an autonomic storm). Typical sequence: a cholinergic phase (salivation, sweating, bradycardia, vomiting), then a prolonged adrenergic phase (hypertension, tachycardia, myocardial injury, pulmonary edema) that may end in shock. Centruroides venom also causes neuromuscular hyperactivity in children.

Grading

• I: local pain only
• II: regional symptoms and mild systemic features
• III: moderate, with cranial nerve or neuromuscular dysfunction
• IV: severe, with cardiopulmonary failure

Most deaths occur within 24 hours, in children under 5 years. Complications are cardiogenic shock, pulmonary edema, myocarditis, arrhythmia, seizures, pancreatitis and respiratory failure.

• Immediate burning pain, hypersensitivity and tingling at the site, with little swelling
• Cholinergic features: drooling, sweating, tearing, vomiting, diarrhea, bradycardia, priapism
• Adrenergic features: agitation, tachycardia, hypertension, cold clammy extremities, arrhythmia
• Centruroides in children: abnormal jerking and roving eye movements, tongue fasciculation, dysphagia, restlessness
• Dyspnea and pulmonary edema, then hypotension and shock
• Red flags: a child under 5 years, vomiting that persists, respiratory distress, cold peripheries, and a heart rate under 50 or over 150 beats a minute

1. Clinical diagnosis from the sting, identification of the scorpion and the grade.
2. Monitoring: blood pressure, heart rate, oxygen saturation, and temperature.
3. ECG (ST-T changes, arrhythmia, conduction block), troponin, creatine kinase-MB, and echocardiography (reduced left ventricular ejection fraction).
4. Blood tests: glucose (hyperglycemia), electrolytes, amylase and lipase, creatinine, creatine kinase and blood gases.
5. Chest radiograph if dyspneic.

Differentials: organophosphate poisoning, other envenomation, anaphylaxis, myocarditis, sepsis, hyperthyroidism, tetanus.

1. Local care: clean the wound, apply cold compresses, and avoid tourniquets, incision and suction. Paracetamol 1 g orally every 6 hours (children 15 mg/kg), and lidocaine 1% 1 to 5 mL infiltrated without epinephrine or by regional block. Tetanus toxoid 0.5 mL IM if not immunized.
2. Antivenom (for grade III and IV and for children with systemic features):
   • Centruroides F(ab')2 antivenom: 3 vials IV over 10 minutes in 50 mL of saline, then 1 vial every 30 to 60 minutes if symptoms persist.
   • Androctonus, Leiurus and Buthus polyvalent antivenom: 10 mL IV (5 to 20 mL) over 30 minutes, given at the same dose in children.
   • Have epinephrine 0.5 mg IM ready for anaphylaxis, and watch for serum sickness at 7 to 14 days (prednisolone 40 mg orally daily for 5 days).
3. Prazosin (vasodilator, especially for the Indian red scorpion): 30 micrograms/kg orally (adults 1 mg) every 3 hours until the extremities are warm and blood pressure is controlled. Avoid beta blockers.
4. Agitation and neuromuscular hyperactivity: midazolam 0.05 to 0.1 mg/kg IV, repeated as needed, with airway equipment ready.
5. Cardiogenic shock and pulmonary edema: oxygen, non-invasive or invasive ventilation, dobutamine 5 to 20 micrograms/kg/min, and avoid excessive fluids. Sodium nitroprusside 0.5 to 10 micrograms/kg/min for hypertensive crisis.
6. Bradycardia and bronchorrhea: atropine 0.5 to 1 mg IV (children 0.02 mg/kg), used cautiously since it may worsen tachycardia and hypertension.
7. Observation: at least 6 hours in adults and 12 hours in children, and intensive care for grade III and IV.

Prevention: shoes should be shaken out, bedding checked, and bed nets and sealed housing used. Follow-up at 1 to 2 weeks for cardiac function after severe stings.