Page 125 - Journal of Special Operations Medicine - Spring 2015

knowledge, reference medical texts, online resources, or Staphylinidae (rove beetles) effecting humans most sig­
other electronic consultation, one can then proceed with nificantly. Narrowing the focus to insects indigenous
4
developing a working diagnosis and treatment plan. to the East Africa, the likely diagnosis in this case was
Having knowledge of flora and fauna in the AO can Paederus dermatitis.
assist in identifying a potential source and in fine­tuning
the treatment plan. Paederus dermatitis (also referred to as dermatitis lin­
earis and, incorrectly, as “blister beetle dermatitis”) is a
As the differential diagnosis of blistering skin lesions contact irritant dermatitis that is caused by exposure to
can be extensive, the patient’s history and physical ex­ pederin, a vesicating chemical found in the genus Paede-
amination help significantly narrow possible etiologies. rus (Staphylinidae). More than 600 species are found in
5
In this patient, the lesions were localized to a very spe­ temperate and tropical environments; most are are slen­
cific area, making blistering diagnoses with a general­ der, approximately 1cm long, with black heads, orange
ized distribution (i.e., Steven­Johnson syndrome, toxic bodies, and black abdominal tips (Figure 3). Known by
epidermal necrolysis, staphylococcal scalded­skin syn­ common names such as rove beetle, acid bug, Nairobi
drome) unlikely. Similarly, lesions located specifically fly, Kenya fly, and a variety of other names around the
on the posterior aspect of the knee made diagnoses like world, Paederus beetles do not bite, sting, or secrete
dyshidrotic eczema, dermatophytosis, scabies (seen on pederin as a defensive secretion. Chemical exposure oc­
6
the hands and feet), and herpes simplex virus infection curs when the beetle is crushed or brushed away while
unlikely. A history of acute onset in a patient with no on the skin. If the chemical remains on the skin, the
5,7
past medical history nor previous episodes made sev­ characteristic vesicular rash will generally appear in 12–
eral other blistering disorders (e.g., miliaria crystallina, 24 hours, with itching and burning commonly experi­
linear immunoglobulin A bullous dermatosis, bullous enced prior to rash developing. In addition, the pederin
8
systemic lupus erythematosus) also unlikely. can also contaminate other areas of skin through direct
contact. This can be seen across joints as mirror image
Narrowing the differential diagnosis of blistering le­ or “kissing” lesions, when contaminated skin comes
sions further, sunburn and other photodistributed erup­ into contact with uncontaminated skin during range of
tions were unlikely, as the lesions were isolated to a very motion (Figure 4). This can give the impression that the
specific area. Furthermore, there had been no change rash is spreading or that multiple exposures have oc­
in washing detergents, soaps, or use of lotions, and no curred. When contaminated hands transfer the pederin
known exposure to plants, making an allergy or con­ near the eye or area around the eye (or if a beetle lands
tact dermatitis unlikely. The patient did have a history in that area), the resulting painful and swollen eye is
of chicken pox as a child, making herpes zoster a pos­ commonly known as “Nairobi eye” in East Africa. 9
sible etiology. However, the lesions were noted to be on
the medial aspect of the posterior knee, which would Figure 3 Paederus beetle (“Nairobi Fly”).
suggest the scenario of two dermatomes affected (S1
and S2) in a very specific area, without further lesions
in either dermatome. The lack of prodromal pain, acute
onset, and lack of wider distribution along the derma­
tomes made herpes zoster possible but unlikely.

Examining the patient’s history, it was noted that he felt
“a bug” crawling on him in the area prior to the onset
of the pain and rash. While the offender was not seen, a
bite or sting is the most likely diagnosis. As there are a
variety of arthropods worldwide that can cause a spec­
trum of dermatologic manifestations, a working knowl­
edge of the AO’s fauna is critical.

Case Diagnosis

Many of concerning diagnoses have been effectively Treatment
eliminated from the differential, and the likely etiology
of bug bite or sting is apparent. There are a variety of While Paederus dermatitis is generally not considered a
insects that can cause such a presentation with pain, life­threatening condition, it can have significant mor­
erythema, blisters/ vesicles, with beetles in the Meloidae bidity with negative effect on individuals and potentially
(blister beetles), Oedemeridae (false blister beetles), and the mission. Lesions can be painful and irritating, which

A Painful Rash in an Austere Environment 115