Clinical Challenge: Painful Pustules on the Legs

Fire ants (Solenopsis invicta) originated in South America, but now are endemic in much of the southern United States. The ants form mounds and when the mound is disturbed, the ants swarm and will sting simultaneously. Initially, the stings appear...

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Fire ants (Solenopsis invicta) originated in South America, but now are endemic in much of the southern United States. The ants form mounds and when the mound is disturbed, the ants swarm and will sting simultaneously.

Initially, the stings appear as a painful wheals which progresses to painful and pruritic pustules. Topical and intralesional steroids may provide some relief and decrease inflammation. Anaphylaxis is possible in patients with severe allergy to the toxin. Such patients should carry an epinephrine autoinjector with them. 

Bedbugs (Cimex lectularius) are blood-sucking insects that infest homes, hotels, dormitories and other living quarters. Bedbugs are nocturnal, feeding at night.

Bedbug bites appear as pruritic, edematous, pink papules. The bites often appear in groups of three — the so-called “breakfast, lunch and dinner” distribution. Bedbug bites may be treated with topical corticosteroids. Eliminating the infestation often requires professional exterminators. 

The most common variant of black widow spider in North America is Lactrodectus mactans. It is a large black spider.  The females have a red hourglass mark on their abdomen. Only adult female spiders are capable of envenomation. Pain and swelling occur at the injection site. The lactrotoxin venom may then cause muscle spasms, acute abdominal pain, headache and nausea. 

The brown recluse spider (Loxosceles recluse) has a characteristic brown violin-shaped marking on the cephalothorax. The bite is often initially painless with pain developing hours later. Cutaneous necrosis may occur at the site of the bite. In severe cases, patients may develop disseminated intravascular coagulation or even shock. 

Adam Rees, MD, is a graduate of the University of California Los Angeles School of Medicine and a resident in the Department of Dermatology at Baylor College of Medicine also in Houston.

References

1. Bolognia J, Jorizzo JL, Schaffer J. “Chapter 85: Bites and Stings.” Dermatology. St. Louis, Mo.: Mosby/Elsevier, 2012.
2. James WD., Berger TG, Elston DM. “Chapter 20: Parasitic Infestations, Stings, and Bites.” Andrews’ Diseases of the Skin: Clinical Dermatology. Philadelphia: Saunder Elsevier, 2011.