Sea urchins belong to the phylum Echinodermata and are nonaggressive, slow-moving creatures. Envenomation usually occurs after accidental contact with the organism. Long, brittle, venom-filled spines or specialized jaw-like appendages (pedicellariae) are responsible for the injury. Other echinoderms, notably the crown of thorns starfish, may also cause injury via similar mechanisms. The spines frequently break. Pedicellariae can remain attached and active for several hours. They may advance into muscle or joint spaces and cause infection or injury from the venom. The usual presentation is burning pain progressing to localized muscle aches. Erythema and edema may be present. Multiple envenomations may produce systemic symptoms including nausea, vomiting, abdominal pain, paresthesias, numbness, paralysis, hypotension, syncope, or respiratory distress. While envenomation causes a reaction that may be quite painful, deaths, though reported, are exceedingly rare.
Management and Disposition
Following envenomation, the affected area should be submersed in hot water (43°C-46°C [109°F-115°F]) for 30 to 90 minutes. Pedicellariae may be removed by applying shaving cream and gently scraping with a razor. Obvious embedded spines should be removed. An x-ray should be performed to rule out retained foreign body. In certain cases, CT, ultrasound, or magnetic resonance imaging (MRI) may be helpful. Hand wounds often require surgical debridement. Retained spines may dissolve spontaneously, but granulomas may form, producing locally destructive inflammation. Antibiotics may be useful in certain cases. Tetanus prophylaxis should be addressed.
Sea Urchin Spine on X-Ray. This is an x-ray of a patient who was reaching into a rock crevice in the ocean and experienced sudden sharp pain. Note the retained sea urchin spine in the fifth digit adjacent to the proximal phalanx. (Photo contributor: Marion Berg, MD.)
Long-Spined Sea Urchin. The majority of urchins are nonvenomous and only cause injury from puncture wounds. Their spines may break off in the victim, resulting in a high likelihood of infection. (Photo contributor: Ian D. Jones, MD.)
Sea Urchin Envenomation. Note the multiple puncture wounds on the foot of a patient who accidentally stepped on a sea urchin in shallow water. (Photo contributor: Saralyn R. Williams, MD.)
Fire Urchin. A beautiful fire urchin, found in the Indo-Pacific. (Photo contributor: Ian D. Jones, MD.)
Sea urchin envenomation involving a joint may produce severe synovitis.
Some species of sea urchin contain dye, which may give the false impression of a retained spine.
Sea urchins known to be hazardous to humans are generally found in the Indian Ocean, Pacific Ocean, and Red Sea.