November 01, 2011
4 min read
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A 1-year-old female with blister on her left hand

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A 1-year-old female is admitted to the hospital for evaluation and treatment of a large blister on the palm of her hand. The history of the chief complaint began the day before when the patient was found to have a small pustule on her palm that was initially thought to be a possible spider bite that grew at an alarming rate. This prompted a visit to the local ED the next day, from where she was admitted.

James H. Brien, DO
James H. Brien, DO

Her past medical history was that of a previously healthy infant with no significant medical or surgical problems. Her immunizations are up-to-date, and she has had no recent travel, animal exposure or trauma. Her parents report no associated fever and no sick contacts; specifically, no contacts with any similar or other skin sores.

Her examination reveals an alert, playful infant with normal vital signs and whose exam is that of a normal baby, except for the left hand, which has a very large blister-like lesion occupying most of the palm with some surrounding erythema and minimal edema, as shown in Figure 1.

Figure 1
Figure 1: Her exam is that of a normal baby, except for the left hand, which has a very large blister-like lesion occupying most of the palm with some surrounding erythema and minimal edema.

Admitting lab tests include a complete blood count (CBC), with an elevated white blood cell (WBC) count at 19,700 cells/mcL, an erythrocyte sedimentation rate (ESR) of 38 mm/hour and a C-reactive protein (CPR) level of 4.3 mg/L. A plain radiograph just showed soft tissue swelling. The patient was empirically treated with clindamycin plus ceftriaxone on admission.

What’s Your Diagnosis?

A.Spider bite

B.Snake envenomation

C. Staphylococcus aureus abscess

D.Thermal injury

The blister was surgically drained and debrided, revealing methicillin-sensitive Staphylococcus aureus (MSSA) on culture (C). If you are a regular reader of this column, you might recall that I featured a similar case with a lesion on a child’s knee in the July issue (Figure 2) that also turned out to be caused by MSSA. Since that column was published, and I have shown the case at a couple of meetings, I have received feedback from a few of you, including my guest columnist, about similar unusual blistering lesions with cellulitis caused by S. aureus.

Figure 2
Figure 2: A lesion on a child’s knee turned out to be caused by MSSA.

Usually, when a S. aureus infection causes a localized blistering lesion, it is a strain that produces an epidermolytic toxin, causing bullous impetigo or bullous varicella. If the toxin is in the bloodstream, it may result in scalded skin syndrome. Those blisters are typically very thin and easily ruptured because the depth of injury is within the granular layer of the epidermis. The blisters featured in this case, on the other hand (no pun intended), appear to be covered with a thicker layer of skin. There’s probably nothing special about these blistering lesions, but after more than 3 decades of seeing various infections of the skin, it just seems that I would have seen something like this before now.

S. aureus infections of the skin, particularly methicillin-resistant S. aureus, seem to get confused with spider bites. Certainly, spider bites can cause a pustular lesion on the skin, as shown in Figures 3 and 4 taken 1 day apart — an adolescent who actually saw the spider after taking off his shirt. These don’t have to be “poisonous” spiders, such as the brown recluse or black widow. Some common spiders will bite if trapped between you and your clothes, as in this case. This may result in a small pustule, much like the fire ant sting (Figure 5). However, if the lesion goes on to look similar to Figures 6 and 7, with surrounding erythema, swelling and pain, think Staph.

Figure 3
Figure 3

Figure 4
Figure 4: Spider bites can cause a pustular lesion on the skin, as shown in Figures 3 and 4 taken 1 day apart.

Figure 5
Figure 5: Some common spiders will bite if trapped between you and your clothes, as in this case. This may result in a small pustule, much like the fire ant sting.

Figure 6
Figure 6

Figure 7
Figure 7: If the lesion goes on to look similar to Figures 6 and 7, with surrounding erythema, swelling and pain, think Staph.

The victim usually knows when they have been bitten by a snake, but certainly a baby could have an unwitnessed bite and present with findings consistent with an envenomation (pain, swelling, possible blistering and bleeding, depending on the species) such as that shown in Figures 8 and 9 — a patient who had a rattlesnake bite to the hand less than 24 hours earlier. The patient presented had findings more consistent with mild cellulitis surrounding a large blister, rather than massive, diffuse swelling seen in a snake envenomation.

A thermal injury can obviously cause blistering of the skin in the area burned, but the fluid is clear or straw-colored (Figure 10) and not likely to be associated with cellulitis. The patient presented had an unusual, dark blister that should be fairly easy to distinguish from a burn injury.

Figure 8
Figure 8: A baby could have an unwitnessed bite and present with findings consistent with an envenomation depending on the species, such as that shown in Figures 8 and 9.

Figure 9
Figure 9

Figure 10
Figure 10: A thermal injury can cause blistering of the skin in the area burned, but the fluid is clear or straw-colored.

With culture and sensitivity results, the baby presented had her antibiotics changed to an anti-staph penicillin IV for 7 days, followed with an additional few days of oral amoxicillin-clavulanate, with a rapid recovery. Figure 11 shows the appearance of the hand a few days after drainage and debridement, with almost complete resolution of the erythema.

Figure 11
Figure 11 shows the appearance of the hand a few days after drainage and debridement, with almost complete resolution of the erythema.

Columnist Comments

I would like to thank Dr. Maria Bernardo of San Jorge Children’s Hospital in San Juan, Puerto Rico, for contributing this case and for her help in writing this column. She received her undergraduate education at SUNY at Stony Brook, then medical school in Guadalajara, Mexico. Her pediatric residency was at San Juan City Hospital. Dr. Bernardo has been a pediatric hospitalist for the past 11 years.

Maria H. Bernardo, MD, is a pediatric hospitalist at San Jorge Children’s Hospital in San Juan, Puerto Rico. James H. Brien, DO, is Vice Chair for Education at The Children’s Hospital at Scott and White and is the Associate Professor of Pediatrics at Texas A&M University, College of Medicine, Temple, Texas. email: jhbrien@aol.com. Disclosures: Drs. Bernardo and Brien report no relevant financial disclosures.

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