Don’t Miss This! Check this tropical rash

This 45-year-old female presents to your ED after returning home from her vacation to Trinidad where she spent the last 6 days. Yesterday she noticed a linear serpiginous rash on her legs and arms that was slightly painful. Today it has progressed and become somewhat darker and is now pruritic. Activities that she participated in while on vacation included swimming in the ocean, tanning (with SPF 30 sunblock) and water aerobics in the swimming pool. She reports no shortness of breath or difficulty breathing. She has no past medical history, is taking no medications and has no allergies that she knows of. She has no recent new exposures to perfumes, soaps, pets or medications.

Her vital signs are within normal limits. Examining her skin reveals the rash that is pictured. It has numerous thin linear red patches that have been excoriated in some regions due to scratching. For the most part, they are all in the same stage of development and none are raised or filled with fluid. There is no pus present and no lymphadenopathy is palpated. Otherwise, her examination is grossly unremarkable.

Discussion:                                            
It becomes readily apparent that this rash can be one of many different maladies. Numerous environmental, infectious and allergic triggers come to mind. The fact that it is linear helps you narrow down what the cause may be. While chicken pox (Varicella virus infection) can be quite pruritic and occurs all over the body, it generally does not occur in a linear pattern. It also usually follows a prodrome of fever and other URI-type symptoms that this patient did not report. Cutaneous larva migrans (CLM) may be a consideration in this patient. The rash of CLM is often linear and usually itches. Our patient also has a history of walking on sandy, wet terrain in a tropical region recently, giving credibility to this idea. However, what about the fact that this rash started off being painful? Could it then be due to a jellyfish envenomation? Jellyfish account for the most commonly reported marine envenomation. This comes as no surprise with at least one hundred species that are potentially dangerous to humans. Most injuries caused by these invertebrates are trivial, with the majority of victims not bothering to seek out professional medical attention. Envenomations can be serious, however, and for that reason emergency medicine practitioners should be familiar with the management of these injuries. The most notorious, Chironex fleckrei or the box jellyfish, has been associated with sixty-seven deaths and numerous hospitalizations. While this jellyfish is predominantly found in the waters of northern Australia, cases and syndromes related to envenomation from related species have been reported in the Americas1. With increasing ease and speed of travel and tourism, delayed presentations of these injuries could potentially arrive at almost any emergency department in the world.

What other type of rash can be linear and pruritic? A reaction to poison ivy (genus Toxicodendron) may also present in this manner. While the rash of poison ivy may start out as linear red plaques, they rapidly progress on to fluid filled bullae that eventually rupture. The presentation in the history and physical therefore make this entity an unlikely cause of our patient’s rash.

A simple allergic reaction can be considered in the differential diagnosis of our patient. Red patches on the skin progress and become more diffuse and are also quite pruritic. However, the lesions of an allergic reaction are not typically linear but rather are irregular in shape. They also usually become raised unlike the lesions seen on our patient’s extremities.

What if our patient started to develop systemic symptoms like hypotension or difficulty breathing? This presentation might more resemble an allergic reaction. However, it could also resemble a serious form of jelly fish envenomation such as the Irukandji syndrome. A number of species have been associated with the Irukandji syndrome, although Carukia barnesi has been the most firmly linked organism to this rare malady. In 2002, the deaths of two tourists in Queensland were attributed to this syndrome.

So what do we think the correct diagnosis for our patient is? The linear nature of the lesions pushes you away form urticaria or an allergic reaction. The fact that there are no fluid filled bullae strongly suggest that this is not a toxicodendron exposure. Cutaneous larva migrans typically is only found on the feet; picked up from walking on infected soil. This leaves us with the most likely diagnosis being jellyfish envenomation. The history of swimming in the ocean fits and the physical examination can definitely be consistent with a jelly fish envenomation. Occasionally the patient does not see the causative culprit, in which case the diagnosis is suggested only by the dermatologic manifestations occurring some time after swimming.

While toxicodendron leaves have to rub against the skin depositing their oils and causing a type 4 hypersensitively reaction and the worm of CLM actually borough into the skin, jelly fish need only have a piece of a tentacle brush against you. All jellyfish share a similar envenomation mechanism, the microscopic nematocyst. This tiny structure is filled with a variety of neurologic, cytolytic and enzymatic toxins. Contact with or stimulation of the nematocyst results in delivery of the toxins into the skin of the target through a barbed appendage. Millions of nematocysts are densely packed along the jellyfish tentacles at the ready to sting attackers or prey of this animal when contact is made.

Box jellyfish are a special type of cnidarian that should be discussed whenever reviewing the medical management of jelly fish envenomations. They are the most dangerous of all of the jelly fish species. Their venom contains chemicals that are potent dermatologic, cardiotoxic, hemolytic, neurotoxic, myotoxic and in some cases hepatotoxic substances. A frosted linear cross-hatched cutaneous pattern is almost pathognomonic for these envenomations. Encounters are most prevalent in the summer months, although stings have been reported year-round.

Arriving at the diagnosis of cnidarian envenomation can occasionally be challenging. Microscopic identification of the nematocysts is possible, and there are several immunologic tests against antigens of the most common jellyfish; however, these tests are primarily confined to research settings. Therefore, in the end, a good history and physical is usually all that is needed.

Remaining adherent tentacles should be inactivated and then removed to prevent further envenomation from nematocysts. Mechanical manipulation prior to inactivation can result in further elaboration of toxins. Depending on the culprit cnidarian, either vinegar (acetic acid) or baking soda slurries are effective at deactivating the nematocysts. Although traditionally promoted as efficacious, ethanol can result in further discharge and release of toxins, as can urine4 and fresh water5. Rubbing sand onto the wounds has no proven benefit either.

After inactivation, most tentacles can be rinsed off using salt water. For tenacious tentacles, some authors have described the application of shaving cream or paste, and then shaving the area. Alternatively, scraping the victim’s skin with a shell or credit card may be tried6. Thus far, none of these removal techniques have been rigorously investigated head to head. Application of ice packs may help the intense burning associated with stings and may alleviate swelling. Many patients end up requiring morphine for pain control.

After the initial management on the beach, what should be done next? Most patients with jellyfish envenomations will not need to go to a hospital at all. Of those that do, the majority can be safely discharged after several hours of observation and with improving symptoms. More seriously injured patients (e.g., persistent pain, hemodynamic instability, dysrhythmias, respiratory distress, etc.) should be admitted for continued medical management and observation.

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