Sea urchin stings are stab wounds accidentally inflicted by the spines of echinoderms of the class Echinoidea.
The vast majority of patients with sea urchin stings will present to the physician knowing where and how they got injured.
They usually display multiple puncture wounds that may be surrounded be a reddened or bluish area of skin. Additional signs of inflammation, i.e., warmth and swelling, may be observed. Patients often report pain that may manifest as a burning or stinging sensation. Bleeding may occur if the skin was perforated. In severe cases, multiple sea urchin stings may cause considerable blood loss, weakness, fatigue and eventually shock. Moreover, broken spines may be visible in the wound canal.
Systemic symptoms may be displayed by patients who suffered from venomous sea urchin stings. In these cases, local signs of inflammation and pain are usually more pronounced. Pain may last several hours if left untreated. Nausea, vomiting, paresthesias, hypotension, muscular paralysis and subsequent dyspnea have been reported in severe cases .
Mid- to long-term complications of sea urchin stings may consist in wound infection and granuloma formation due to remaining spine components. Skin coloration has been observed and may be explained by diffusion of pigments from dark-colored spines.
There is a variety of pathological conditions that may be associated with sea urchin stings if the respective anatomical structures get punctured. In this context, synovitis, intra-articular granuloma formation and subsequent arthritis have been reported after sea urchin stings with joint involvement. Tenosynovitis may also occur after sea urchin stings  . If the respective wounds become infected, inflammation progresses rapidly.
Diagnosis is most frequently based on data obtained during anamnesis.
A thorough workup may, however, be necessary to correctly assess the extent of tissue damage. Rather simple and inexpensive imaging techniques usually suffice to do so. The wound inflicted by sea urchin spines can often be visualized radiographically. Calcareous spines may be directly visible, but so is the air that is drawn into the wound while getting stung. If X-rays do not provide satisfactory information, an additional ultrasonographic examination can be carried out. This is particularly recommendable if small foreign bodies need to be visualized. Magnetic resonance imaging and computed tomography are usually not necessary.
Persistent pain or worsening conditions regarding involved tendons, joints and other organs, require renewed examination. Tissue samples should be obtained for microbiological culture to rule out infection. Surprisingly, infections are not a common complication of sea urchin stings.
The possibility of the patient suffering from additional diseases that are by no means related to the sea urchin sting should be taken into account.
Spine removal and proper wound care are indicated.
Sea urchin spines should be handled with the utmost care to avoid breaking. They mostly consist of calcium carbonate and magnesium carbonate and therefore dissolve in vinegar. It may be necessary to repeatedly soak a wound in vinegar or to apply vinegar with wound dressings. Surgical removal may be required if the spine penetrated or migrated to deeper tissue layers.
Wound care depends on the extend of the lesion. Superficial lesions, even envenomation by pedicellaria-carrying sea urchins, should be washed before a wound balm is applied. Debridement, potentially surgical debridement may be necessary to treat deeper wounds. In cases of joint and tendon injury, synovectomy and joint debridement or tenosynovectomy may become necessary to treat chronic inflammation.
Analgesics may be administered for a few days. If pain persists, the wound should be revised for infection. If infection is detected, it should be treated with antibiotics. Also, the possibility of remaining foreign material in the wound canal should be considered.
Prognosis is good. Despite their high overall incidence, serious injuries due to sea urchin stings are rare.
Sea urchin stings result from accidental contact or careless handling. The animals move very slow and do not attack humans, they actually feed on algae and periphyton. However, their spines may inflict serious injuries when people step on sea urchins while moving through water or if strong currents or waves force swimmers or divers against them. Wetsuits, neoprene gloves and shoes only provide minimal protection since they are easily perforated by sea urchin spines, even though they avoid direct contact to the stinging, venomous tips of shorter spines and pedicellaria. Some cases regarding curious individuals being stung upon handling sea urchins have been reported.
Sea urchins can be encountered in all seas worldwide and sea urchin stings occur quite frequently. Most cases are reported from subtropical and tropical climates, regions where people use to spend their holidays at the beach. Unfortunately, these are the same regions where venomous sea urchins exist. Species pertaining to the genera of Diadema, Echinothrix, Araeosoma, Asthenosoma, Phormosoma, Toxopneustes and Tripneustes may be particularly dangerous to this end and live in the Indo-Pacific area and the Caribbean. Nevertheless, serious injuries are rare. Indeed, the risk for death due to envenomation induced by sea urchin stings is considered to be low although anecdotal reports of lethal accidents exist   . There may be an increased risk for drowning after being stung by a sea urchin.
The vast majority of sea urchin stings merely causes mechanical damage that may nevertheless be serious, especially if blood vessels or nerves are punctuated or if stings occur in the face.
However, there are several species that dispose of either venomous spines or venomous pedicellaria, as has been indicated in the last section. Echinoidea rarely present both of the aforementioned defense mechanisms. Therefore, venomous sea urchins may be morphologically grouped into three categories:
Sea urchin stings generally result from accidental stepping on or being forced against sea urchins. Unfortunately, neoprene shoes or similar protective gear may easily be perforated by sea urchin spines. Therefore, it should be avoided to move through waters where sea urchins may live when visibility is poor, e.g., because the water is turbid or at night.
Some cases of sea urchin stings concern careless handling of these animals. Tourists should not have to touch these animals at all. If sea urchins need to be handled, thick gloves should be worn.
The common name of echinoderms of the class Echinoidea is sea urchins. There are almost 1,000 species of sea urchins and they are distributed all over the world. Their most striking morphological feature is their spines. They form part of their skeleton and may differ widely between distinct species in number, length and appearance. Additionally, they dispose of a jaw-like structure that presumably enables them to defend themselves, maybe also to hunt. This structure is called pedicellaria. Spines or pedicellaria may be venomous.
The majority of sea urchin stings causes mechanical damage. The human immune defense may react particularly strong to spines that break off upon contact and that remain in form of a foreign body inside the patient's tissue. Serious injuries may result from damage to blood vessels or nerves. If parts of the spine are not removed from the initial stab wound, they may migrate to deeper tissue layers and provoke the development of granuloma . Furthermore, the skin may take on a reddish or bluish tone at the site of injury. Edema may be detectable and patients sometimes experience pain or a burning sensation  .
Diagnosis is based on anamnesis. In geographic regions where venomous sea urchins exist, it may be necessary to identify the species that accounts for the respective sea urchin sting. If necessary, imaging techniques can be used to locate spines that have penetrated the skin. Spines should be removed. Complete removal usually improves the patient's condition, but may be difficult to achieve due to their fragility .
There are almost one thousand different species of sea urchins and they can be encountered in all seas of the world. However, few sea urchin species are venomous and all these species live in the Indo-Pacific seas or in the Caribbean. Venom may be applied by means of more or less long spines, but also via small, jaw-like structures called pedicellaria. Indeed, the most venomous sea urchin does not have any spines at all.
People tend to accidentally step on sea urchins when wading through water, particularly in subtropical and tropical climates where they spend their holidays at the beach. Even protective clothes such as wetsuits or neoprene shoes are not sufficient to protect oneself from sea urchin stings. The only effective measure to avoid these painful experiences is to not move through water when visibility is low.
Some sea urchin stings result from surfers, divers and other persons doing water sports being pressed against sea urchins by strong currents or waves. It is best to avoid such regions.
Careless handling of sea urchins may also result in injury. Tourists should not touch sea urchins and if animal caretakers need to handle them, they should wear thick gloves.
Sea urchin stings occur quite frequently, but luckily, the majority of cases is not severe. A burning sensation and pain at the site of injury is usually accompanied by redness, warmth and swelling.
These same symptoms occur after getting stung by a venomous sea urchin, but they may be more pronounced. Pain may last several hours. Nausea, vomiting, decreasing blood pressure and overall weakness may also be experienced. In isolated cases, people drown after getting stung by a sea urchin. Otherwise, no direct relation between sea urchin stings and death has been demonstrated.
Diagnosis is based on the patient's history. A more thorough workup may become necessary if there is the involvement of major blood vessels, nerves, tendons, joints or other important anatomical structures.
Treatment consists in spine removal and wound care. The spine should be handled with the utmost care because it breaks easily. Then, small spine components could remain in the skin and cause chronic inflammation and formation of granulomas. Superficial wounds will be washed, deeper wounds require more intensive wound cleansing. Sea urchin spines dissolve in vinegar and thus repeated application of vinegar to the wound may be helpful. Surgical interventions may become necessary if any of the above mentioned anatomic structures was compromised by the sea urchin sting.