Stonefish Envenomation

Stonefish (Synanceia verrucosa and S. horrida) are the most venomous fish in the world. They live in shallow Indo-Pacific reefs, tidal flats and estuaries, including the East African coast. They are camouflaged and lie motionless on the sea floor. Thirteen dorsal spines are connected to venom glands, and the pressure of a footstep releases venom.

Venom proteins (verrucotoxin, stonustoxin and hyaluronidase) form pores in cell membranes, causing intense pain, cardiovascular depression and neuromuscular effects. This is among the most painful of all envenomations. Pain peaks in 30 to 90 minutes and can last 6 to 48 hours. Deaths are rare, from pulmonary edema, shock or arrhythmia, and fewer than 5% have systemic effects.

Complications: tissue necrosis, secondary infection (Streptococcus, Staphylococcus, Vibrio and Mycobacterium marinum), retained spine fragments, cellulitis, osteomyelitis and chronic pain.

• Immediate excruciating pain radiating up the limb, with puncture wounds
• Marked swelling of the whole limb, pallor then cyanosis around the puncture, blistering and numbness
• Nausea, vomiting, sweating, headache and delirium
• Hypotension, bradycardia or other arrhythmia, dyspnea, seizures and, rarely, paralysis
• Red flags: hypotension, arrhythmia, dyspnea, multiple punctures and a delay of over 12 hours with spreading erythema

1. Clinical diagnosis from the history of wading and the pain.
2. Radiograph or ultrasound for retained spine fragments.
3. ECG and electrolytes, and creatine kinase for muscle injury.
4. Wound culture when infected.

Differentials: scorpionfish and lionfish stings, stingray injury, sea urchin puncture, fracture, other marine envenomation.

1. First aid: remove from the water, immobilize the limb and avoid tourniquets.
2. Hot water immersion at 45 degrees Celsius (test on an unaffected limb to avoid scalding) for 30 to 90 minutes until pain is relieved. The venom is heat-labile, and this is the most effective first aid.
3. Analgesia:
   • Paracetamol 1 g orally every 6 hours.
   • Morphine 0.05 to 0.1 mg/kg IV titrated, or fentanyl 0.5 to 1 microgram/kg IV.
   • Regional block (digital or ankle) or infiltration with lidocaine 1% 5 to 10 mL without epinephrine, or bupivacaine 0.5% (maximum 2 mg/kg) for longer relief.
4. Antivenom (equine, 2000 units an ampoule): 1 ampoule for 1 to 2 punctures, 2 for 3 to 4 punctures and 3 for more than 4, given by slow IV infusion in 100 mL of saline over 15 to 30 minutes (IM if IV access is not possible), at the same dose in children. Have epinephrine 0.5 mg IM ready for anaphylaxis.
5. Wound care: irrigate, explore under regional block, remove spine fragments, debride and leave open. Tetanus toxoid 0.5 mL IM if not immunized.
6. Antibiotics for deep punctures and delayed presentation: ciprofloxacin 500 mg orally twice daily with doxycycline 100 mg orally twice daily for 5 to 7 days (children over 8 years, doxycycline 2 mg/kg twice daily, and under 8 years, co-trimoxazole 4 mg/kg of trimethoprim twice daily).
7. Systemic effects: IV crystalloid 20 mL/kg for hypotension, atropine 0.5 to 1 mg IV (children 0.02 mg/kg) for bradycardia, dopamine 5 to 20 micrograms/kg/min for persistent hypotension, and cardiac monitoring for at least 6 hours.

Observe for 6 to 12 hours, and admit patients with systemic features. Counsel on thick-soled footwear when wading and shuffling the feet in shallow water.