A 16-year-old boy is brought to the office due to a rash on his chin. The boy sustained a minor cut while shaving with his father's razor 4 days ago. The patient was also using a new shaving cream at the time. The bleeding stopped with minimal pressure. The surrounding skin appeared red the next day. Since then, the affected area has increased in size, become tender, and appeared "wet." This morning, the rash is "dry and crusty." The patient has a history of acne vulgaris and uses a topical retinoid and benzoyl peroxide on his forehead and cheeks. He also periodically develops "cold sores" when experiencing stress, such as before tests at school. He takes no other medications and has no known allergies. Temperature is 37 C (98.6 F). Physical examination shows a well-appearing adolescent in no distress. Skin examination reveals inflammatory acne on the cheeks and forehead. The rash on the chin is shown in the exhibit. Which of the following is the most likely diagnosis in this patient?

Question

A 16-year-old boy is brought to the office due to a rash on his chin.  The boy sustained a minor cut while shaving with his father's razor 4 days ago.  The patient was also using a new shaving cream at the time.  The bleeding stopped with minimal pressure.  The surrounding skin appeared red the next day.  Since then, the affected area has increased in size, become tender, and appeared "wet."  This morning, the rash is "dry and crusty."  The patient has a history of acne vulgaris and uses a topical retinoid and benzoyl peroxide on his forehead and cheeks.  He also periodically develops "cold sores" when experiencing stress, such as before tests at school.  He takes no other medications and has no known allergies.  Temperature is 37 C (98.6 F).  Physical examination shows a well-appearing adolescent in no distress.  Skin examination reveals inflammatory acne on the cheeks and forehead.  The rash on the chin is shown in the exhibit.  Which of the following is the most likely diagnosis in this patient?

Quizplus · Accepted Answer

Explanation: 11ec2b69_be8c_9f72_8f63_810b11d9a965_MD0005_00 Impetigo is a contagious, superficial skin infection most commonly caused by Staphylococcus aureus or Streptococcus pyogenes. Infection often develops within superficial wounds, such as in this patient with a facial cut. It can also develop from any break in the skin, such as with eczema or insect bites. Presentation includes erythematous pustules that subsequently develop a classic, thick honey-colored crusting. Lesions may be painful or pruritic. Diagnosis of impetigo is clinical. Topical antibiotics (eg, mupirocin) alone can treat isolated, small areas of infection, whereas oral antibiotics (eg, cephalexin) are warranted for extensive infection. (Choice A) Contact dermatitis presents with pruritic, painful erythema in an area exposed to an allergen or irritant. Although this patient was exposed to a new product, the slow spread of this localized rash with overlying crusting makes contact dermatitis unlikely. (Choice B) Erysipelas is also a superficial skin infection but presents with well-demarcated, bright red erythema, classically on the cheeks. This patient's rash with overlying crusting is classic for impetigo. (Choice C) Herpes simplex infection presents with clusters of painful vesicles, typically along the vermilion border of the lip. This patient's facial rash is located on the chin, is not vesicular, and has an adherent crusting characteristic of impetigo. (Choice E) Tinea barbae is a dermatophyte infection that presents in the distribution of a beard in men. Although this contagious disease can be spread via shared razors, examination reveals a scattered folliculitis with erythematous papules and pustules, not honey-colored crusting. Educational objective: Impetigo is a contagious, superficial skin infection that presents with erythematous pustules and a classic overlying honey-colored crust. References: Impetigo. (http://www.ncbi.nlm.nih.gov/pubmed/28613693)

A 16-Year-Old Boy Is Brought to the Office Due to a Rash