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Organizations
American Academy of Dermatology
Am. Journal of Trop. Med & Hygiene
Armed Forces Pest Management Board
Blackwell Publishing
Broward Health Medical Center
Bugwood Network
Centers For Disease Control and Prevention
Centro Internacional de Entrenamiento e Investigaciones Mèdicas (CIDEIM)
Dermatology Online Journal
East Carolina University (ECU), Division of Dermatology
International Atomic Energy Agency
Massachusetts Medical Society
NYU Department of Dermatology
Oregon Health & Science University (OHSU)
Oxford University Press
Radiological Society of North America
Washington Hospital Center
Wikipedia
World Health Organization
Paederus dermatitis (PD), also known as dermatitis linearis, is a specific type of irritant contact dermatitis caused by exposure to pederin, a potent vesicant contained in the hemolymph of beetles of the genus Paederus. The condition is characterized by erythematous patches with vesiculobullous lesions that appear suddenly, often overnight, on exposed areas of skin and self-resolve over the course of 1-3 weeks.
The Paederus beetle does not sting or bite, but accidental contact with or crushing of the beetle on skin results in the release of the coelomic fluid containing the irritant pederin. Initially painless, over the course of 12-36 hours, the contact site begins to burn, sting, and itch.
Erythematous patches first appear and are followed by vesicles, which coalesce into bullae over the course of several days. Affected areas appear similar to chemical or thermal burns, but the clinical symptoms of burning and itching are relatively mild and disappear within a few days. The skin manifestations persist 1-3 weeks as vesicles, pustules, and bullae; lesions then crust, scale, and eventually desquamate without scarring. Postinflammatory hyperpigmented patches are transient but may last months. Atypical variants may present with more systemic skin involvement and symptoms of more severe burning and itching, fever, neuralgia, arthralgia, and vomiting.
PD size, shape, severity, and location are case dependent but typically involve exposed skin. Periorbital involvement is common, with unilateral periorbital edema and keratoconjuctivitis due to secondary transfer of the irritant from the hands to the face (referred to as Nairobi eye in East Africa).
Paederus beetle species are distributed worldwide, typically living in moist environments (eg, near lakes, marshes, and flood plains) and hot, tropical climates, scavenging debris and the larvae of other insects. While they are able to fly, they prefer to run, characteristically curling when disturbed. The beetles are 7-10 mm long, 0.5-1 mm wide, and are recognized by their distinct black head, red-orange abdomen, black posterior tip of abdomen, and metallic blue or green wings. Paederus beetles are nocturnal and are attracted to artificial lighting, particularly ultraviolet lights (eg, insect electrocution devices) and white lights (eg, fluorescent lights).
PD has a wake-and-see presentation, with beetle exposure occurring inadvertently overnight and skin manifestations appearing in the morning. Patients may not recall seeing any arthropods and will deny recent stings or bites. Incidence of PD is seasonal, with rates peaking during the spring and summer and dropping off significantly as ambient temperatures decrease during the fall. Risk factors include outdoor activities (eg, agriculture, gardening, or military patrols) and working at night in well-illuminated areas (eg, security guards). While the rapid appearance of vesicles and bullae can be concerning, PD often has a mild clinical course that self-resolves over several weeks. Early identification can prevent unnecessary diagnostic tests and treatments and help avoid further outbreaks.
Codes
ICD10CM: L23.89 – Allergic contact dermatitis due to other agents
SNOMEDCT: 402149002 – Dermatosis due to beetle
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Differential Diagnosis & Pitfalls
Cantharidin dermatitis (blister beetle dermatitis) – Meloidae and Oedemeridae beetle families produce cantharidin, another potent vesicant. Cantharidin dermatitis blisters within 24 hours of exposure and is distinguished by its noninflammatory vesicles and bullae compared with the intensely erythematous skin associated with PD.
Phytophotodermatitis – Linear or haphazard erythema and edema that may be accompanied by delayed blister formation. Recent plant exposure.
Thermal burns or chemical burns (chemical burns are covered individually according to chemical agent, eg, hydrogen fluoride burn) – Symptoms of burns are more severe and will have a longer clinical course. Multiple cases of PD have been mistaken for chemical weapon exposure (eg, vesicant exposure) following nighttime military exercises and patrols due to similar presentation.
Herpes zoster – Follows unilateral dermatomal pattern, preceded by a history of varicella. Tzanck smear and direct fluorescent antibody (DFA) positive.
Herpes simplex – Discrete groupings of painful vesicles. Tzanck smear and DFA positive.
Bullous impetigo – Painful red rash with fragile bullae and honey-colored crusting. Gram staining of blister fluid will reveal gram-positive cocci. It may be difficult to distinguish from PD that has become secondarily impetiginized.
Preseptal cellulitis – Periorbital swelling and redness. Patient may appear toxic and febrile and have significant leukocytosis. Eyelid is often warm to the touch.
Angioedema – Edema of the subcutaneous or submucosal tissues involving eyelids (bilaterally), lips, and tongue. Transient, with swelling in less than 24 hours.