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10-year-old female presents with nonhealing ulcerative lesion on shin
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A 10-year-old female is referred for a nonhealing ulcerative lesion on her left anterior shin. The onset was about 1 month ago, when she woke up in bed to find a blistering lesion of the same size and shape. The parent took a picture of the blistering lesion when it was first seen, which had been covered with a Tegaderm bandage (Figure 1).
When she was taken to the first urgent care visit, the provider drained the blister, which the mother said was not stained or cultured because the fluid was clear. Over the next several weeks, she was seen and treated with two courses of oral antibiotics (cephalexin and clindamycin), along with topical mupirocin, without improvement.
Source: James H. Brien, DO
The patient’s past medical history is that of a healthy female with no prior skin problems and no history of trauma to this area of the lesion. She denies swimming or having her legs in any natural body of water in the last year, and she knows of no insect bites in this area. There are no other lesions anywhere else on her skin surface. She described the sore as being somewhat painful at the onset, but it now has only minimal pain with firm palpation.
Her examination, when you see her several weeks after the onset, reveals a linear, ulcerative lesion with no surrounding erythema or swelling, or any significant pain (Figure 2). The rest of her exam is completely within normal limits.
Laboratory tests done before the referral include a complete blood count, C-reactive protein, comprehensive metabolic panel, and erythrocyte sedimentation rate, all of which are within normal limits, and a surface culture of the lesion had grown three different organisms, including Enterobacter cloacae, Enterococcus faecalis and Corynebacterium species. These were thought to be surface contaminants. Plain radiographs of the leg are also normal.
What’s your diagnosis?
A. Mycobacterium marinum infection
B. Group A streptococcal cellulitis
C. Bullous impetigo
D. Blister beetle sore
Case Discussion
While there is no test to prove this condition, the patient history and physical examination are highly consistent with a blister beetle sore. This cutaneous injury results as a consequence of contact with a vesicant called cantharidin, which is produced by several species of blister beetles. If a skin biopsy is performed at the time of the injury, one might see acantholysis in suprabasal keratinocytes with necrosis. However, late in the course of the injury (as in this case) a biopsy may be nondiagnostic. This patient underwent a superficial punch biopsy that revealed subcutaneous fat necrosis with overlying dermal fibrosis with no evidence of infection. There is no specific treatment except to protect the lesion from further injury and allow time for it to heal. The parent was good enough to forward another picture taken with a cell phone camera showing some scar formation (Figure 3), filling in the previously noted linear ulcerative lesion. For those who keep these old columns, a different case of blister beetle dermatitis was featured in my September 1993 column.
Mycobacterium marinum is a type of nontuberculous mycobacteria that can result in a chronic, ulcerative lesion. This lesion typically begins because of a minor skin injury with coincident submersion of the site in water that is contaminated by this organism. It usually begins as a papular lesion that slowly progresses to a granulomatous lesion and ulceration over a period of weeks to months. It is typically treated with clarithromycin, often with rifampin added.
Group A streptococcal cellulitis is a common cause of minor skin infection such as impetigo. However, it is a very common cause of lymphangitis and erysipelas, and is frequently implicated in the development of necrotizing fasciitis. Often, cellulitis may produce similar-appearing blisters with clear fluid, as shown in Figure 4. However, the fundamental difference would be the surrounding erythema and possible streaking of lymphangitis (Figure 5).
Bullous impetigo is almost always caused by an epidermolytic toxin-producing strain of Staphylococcus aureus, resulting in localized blister production. Gram’s stain or culture of fluid from one of these lesions usually reveals the organism, and the lesion usually responds readily to antistaphylococcal antimicrobial therapy.
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- James H. Brien, DO, is with the department of infectious diseases at McLane Children’s Hospital, Baylor Scott & White Health, Texas A&M College of Medicine in Temple, Texas. He also is a member of the Infectious Diseases in Children Editorial Board. Brien can be reached at: jhbrien@aol.com.
Disclosure: Brien reports no relevant financial disclosures.