Sea urchins

Background

Sea urchins are marine invertebrate echinoderms
Found world wide in both shallow and deep waters
Anatomy consists of soft viscera surrounded by a hard plated body ( called a "test") with protruding venomous spines and venomous pedicellariae
Around 950 known species and some are venomous^[1]
- Nonvenomous species have blunt, rounded spines
- Venomous species have sharp, hollow, thin spines
- Some have pedicellariae with sharp jaws and venom glands

Mechanism

Nonvenomous spines cause direct trauma
Venoms are known to contain proteases, hemolysins, steroid glycosides, serotonin, cholinergic substances, and rarely neurotoxins
Pedicellariae attach to the victim and break off from the urchin, releasing venom for several hours

Clinical Features

Black sea urchins (Echinometra lucunter). Below: spinesin the feet of bathers. Right: hyperkeratotic noduleson the hands of a diver who suffered several injuries caused by black sea urchins (foreign body granuloma).

Minor to severe pain the the site of the embedded spine
- They commonly break off, causing hyperpigmentation of the skin and secondary infection^[2]
Venomous spines and pedicellariae generally cause much more severe pain and may be accompanied by systemic signs and symptoms with a significant envenomation including pruritus, nausea, vomiting, abdominal pain, respiratory distress, paresthesias, muscle weakness, and hypotension
Rarely severe envenomations can lead to death

Differential Diagnosis

Marine toxins, envenomations, and bites

Toxins
- Ciguatera
- Scombroid
- Tetrodotoxin (e.g. pufferfish)
- Shellfish poisoning
  - Amnesic shellfish poisoning
  - Diarrheal shellfish poisoning
  - Neurotoxic shellfish poisoning
  - Paralytic shellfish poisoning
Stingers
- Stingray injury
Venomous fish
- Cone shell
- Lionfish
- Sea urchins
- Crown-of-Thorns Starfish
- Stonefish
- Other: Catfish, zebrafish, scorpion fish
Nematocysts
- Coral reef
- Fire coral
- Jellyfish (Cnidaria)
  - Box jellyfish
    - Irukandji syndrome
  - Sea wasp
- Portuguese man-of-war
- Sea anemones
- Seabather's eruption
Phylum porifera (sponges)
Bites
Infections
- Vibrio species in saltwater
- Aeromonas species in freshwater

Evaluation

Clinical diagnosis
Plain films of the injured areas to locate embedded spines
- Evaluate for intraarticular spines
- Ultrasound may be useful if none are seen but radiolucent FB is suspected
- MRI can also locate spines not seen on plain film

Management

Emersion in non-scalding water up to 45°C & Local lidocaine for pain control
Prompt removal of pedicellariae
Remove spines/foreign bodies
- Attempts to remove spines are often futile due to their fragile and friable nature.
- Some areas may have an appearance of a spine due to "tattooing" of the skin^[3]
- If spines are intraarticular or near neurovascular structures they need to be carefully removed in the OR
Thorough irrigation
Update tetanus vaccination if needed
Prophylactic antibiotics for deep puncture wounds

Disposition

Depends on the extent and location of injury and degree of envenomation

Complications

Retained spines
Infection (Vibrio species)
Granuloma and cyst formation

External Links

References

↑ Auerbach P. Chapter 73. Envenomation by aquatic invertebrates. In: Auerbach P. Wilderness Medicine.
↑ Hauglid, Christopher, DO, et al. “EMERGEN-SEA MEDICINE: An Overview of Sea Urchins, Coral, Starfish, and More.” ACEP Now, vol. 40, no. 7, 2021, pp. 8–9.
↑ Hauglid, Christopher, DO, et al. “EMERGEN-SEA MEDICINE: An Overview of Sea Urchins, Coral, Starfish, and More.” ACEP Now, vol. 40, no. 7, 2021, pp. 8–9.

Authors:

[1] Auerbach P. Chapter 73. Envenomation by aquatic invertebrates. In: Auerbach P. Wilderness Medicine.

[2] Hauglid, Christopher, DO, et al. “EMERGEN-SEA MEDICINE: An Overview of Sea Urchins, Coral, Starfish, and More.” ACEP Now, vol. 40, no. 7, 2021, pp. 8–9.

[3] Hauglid, Christopher, DO, et al. “EMERGEN-SEA MEDICINE: An Overview of Sea Urchins, Coral, Starfish, and More.” ACEP Now, vol. 40, no. 7, 2021, pp. 8–9.

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