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Sea Urchins: Beware the Bearers and Wearers of Spines

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By Dr. Ed Maeyens

Egg clusters of the sea urchin Paracentrotus lividusare considered a delicacy in Italy. There they are called "frutti di mare," and while the edible components of this echinoderm are harmless, their spines are not.

Sea urchin injuries are fairly common but infrequently result in dramatic sequelae (after-effects of an injury or disease). This article will clarify the spectrum of local (skin) and systemic reactions to encounters with sea urchin spines.

Structure of Sea Urchin Spines

Spines possess an indented base which fits like a ball-and-socket joint over a tubercle (protuberance) of the urchin’s spherical shell. Muscle fibers wrap around the tubercle and facilitate movement. Each spine has neural innervation. As a spine is stimulated, neighboring spines bend in concert. Most spines are solid with a blunt tip, but in some species, they are hollow with sharp tips. They contain a venom which can include a neurotoxin and/or a cardiovascular toxin. The spine surface is covered by a thin layer of tissue. The chemical composition of the spine is 94 percent mineral (calcium carbonate, magnesium carbonate and silica) and 6 percent organic matter.

Clinical Manifestations of Punctures

Injuries usually occur from inadvertent contact with the spines. Initially only minor discomfort is perceived, but within 15-30 minutes the pain crescendos and can last for several hours. Fragile remnants of broken spines either remain within the skin or are extruded spontaneously. The skin responds by becoming red and swollen around the puncture site. Spontaneous resolution usually occurs in a few weeks: residual spines can be reabsorbed by the body, or they can be extruded from the skin.

Occasionally, delayed skin reactions occur. These include papules and nodules that may appear months after the injury. They are either flesh-colored or slightly purple and are firm to the touch.

A unique complication of spine punctures to the small joints of hands and feet is called tenosynovitis, inflammation of the joint tendons and joint space lining. It is the result of some components of the spine or its covering being implanted directly into either the joint space or tendon. This process can occur immediately after the injury or several weeks later. If this type of injury is not corrected promptly, it becomes chronic and can destroy the joint space.

Tenosynovitis becomes obvious as the joint becomes swollen, red and painful. Spine fragments may infrequently be revealed on x-rays of the joint or tendon. Systemic reactions can occur, but they are rare, characterized by nausea, respiratory distress, muscle weakness, ataxia (an inability to coordinate voluntary muscular movements), syncope (fainting, lightheadedness) and paresthesia (skin tingling, prickling).

Local Tissue Reaction

The unifying reaction pattern to sea urchin spine impalement is the development of a sarcoidal granuloma (nodular, chronically inflamed tissue) at the injury site. The sarcoidal response is a soft tissue reaction that serves to dissolve any spine components left behind. It does so by creating an inflammatory response composed of various cell types. The end result is a dense, nodular collection of inflammatory cells that is evident both microscopically and clinically. If left unchecked this inflammatory process can become destructive. The stimulus for sarcoidal granuloma production is unclear, but has been suggested to be secondary to remnants of either the epithelial spine covering or associated slime, sand, surface microbes (bacteria, algae, etc.) or spine fragments.

Responses to Sea Urchin Spine Injuries

- Acute injury with local pain and swelling, followed by prompt, spontaneous resolution

- Acute injury with secondary infection

- Delayed sarcoidal granuloma formation

- Envenomation-producing systemic symptoms

- Systemic illness as a complication of late onset tenosynovitis

- Complications of small joint spine implantation resulting in swelling and joint destruction. Large join spine implantation produces inflammation and swelling without destruction.


Therapy varies with the injury. If a spine is able to be removed, do so gently and meticulously, as spines are fragile and break readily. Treat pain with analgesics; treat infection with antibiotics.

There are numerous anecdotal treatments that range from washing the site with urine, ammonia or hot mud to applying poultices and skin softeners. No scientific data supports any of these treatments.

Common sense should prevail. Avoid punctures by being aware of sea urchins and wearing protective footwear when wading in shallow waters. If a joint space has been punctured by a spine, seek medical help promptly — this can mean the difference between a temporary problem and the loss of joint function. And if a granuloma appears on a joint, seek medical evaluation.

Sarcoidal granulomas respond well to intralesional corticosteroids when limited to skin, but poorly if in joint spaces. Treatments of systemic reactions must be tailored to the individual’s signs and symptoms.

DAN Member Edgar Maeyens Jr., M.D., is a board-certified dermatologist, dermapathologist and dermatologic surgeon.

- from the March/April 2000 issue of Alert Diver