An 8-year-old boy is brought to the office due to a lower extremity skin rash for the past 3 days. The rash began as tender papules that quickly progressed to form vesicles and flaccid bullae that rupture easily. The patient has no mucosal lesions or other rashes and has never had similar symptoms before. He is up to date with recommended vaccinations and takes no medications. Skin examination findings are shown below. Which of the following is the most likely cause of this patient's skin findings?

Question

An 8-year-old boy is brought to the office due to a lower extremity skin rash for the past 3 days.  The rash began as tender papules that quickly progressed to form vesicles and flaccid bullae that rupture easily.  The patient has no mucosal lesions or other rashes and has never had similar symptoms before.  He is up to date with recommended vaccinations and takes no medications.  Skin examination findings are shown below.  Which of the following is the most likely cause of this patient's skin findings?

Quizplus · Accepted Answer

11ec160b_3905_42a3_9249_8322f5a560f1_MD0001_00 This child has a blistering skin rash with tan- to honey-colored crusts, consistent with bullous impetigo (BI). BI is a superficial infection by Staphylococcus aureus that is most common in young children. It is spread by direct contact, with the greatest incidence in warm, humid, crowded environments. Nonbullous impetigo is a similar syndrome with pustules and crusting but without significant blistering. Either form may occur in healthy skin (primary impetigo) or broken/inflamed skin (secondary impetigo). The blistering in BI is caused by production of exfoliative toxin A, a serine protease that targets desmoglein 1 in the superficial epidermis, by some strains of S aureus. Desmoglein is a cadherin component of desmosomes in epidermal cellular junctions; disruption by exfoliative toxin A causes a loss of cell adhesion and leads to formation of flaccid bullae. Exfoliative toxin A is also responsible for staphylococcal scalded skin syndrome, which presents with generalized erythema and flaccid bullae in flexural areas. (Choices A and B) Bullous pemphigoid is an autoimmune disorder associated with antibodies against hemidesmosomes and is characterized by tense, subepidermal blisters. Pemphigus vulgaris is characterized by intraepithelial cleavage and is due to autoantibodies against desmosomes (desmogleins 1 and 3); it presents with flaccid bullae, desquamation, and oral ulcerations. Both disorders cause scattered or widespread (rather than localized) lesions and are uncommon in children. (Choice D) Atopic dermatitis is associated with mutations in epidermal barrier proteins, leading to increased exposure to environmental antigens and immune hypersensitivity. It typically presents in infants and young children with erythematous papules and plaques involving the head, trunk, and extensor surfaces, and in older children and adults with lichenification in a flexural distribution (eg, neck, wrists, antecubital and popliteal fossae). (Choice E) Herpes simplex virus infection is characterized by recurrent clusters of mucocutaneous papules and vesicles that evolve into ulcerated and crusted lesions. It typically causes localized perioral or genital lesions rather than involving large regions on the extremities. Educational objective: Bullous impetigo is a superficial infection by Staphylococcus aureus that is most common in young children. It is characterized by a blistering skin rash with tan- to honey-colored crusts. The blistering in bullous impetigo is caused by exfoliative toxin A, which targets desmoglein 1 in epidermal cellular junctions and causes a loss of cell adhesion. __________ References: Exfoliative toxins of Staphylococcus aureus. (http://www.ncbi.nlm.nih.gov/pubmed/22069631) Autoimmune and infectious skin diseases that target desmogleins. (http://www.ncbi.nlm.nih.gov/pubmed/20467217)

An 8-Year-Old Boy Is Brought to the Office Due to a Lower