A 4-year-old girl has had an exudative, encrusting skin eruption on her upper lip and both cheeks for more than a week. Her mother has applied a 0.5% hydrocortisone cream twice daily, but says the rash is getting worse. The most likely diagnosis and best treatment is:
Acne vulgaris → treat with tetracycline, 25 mg/kg every 6 hours for 7 days.
+Impetigo contagiosa → treat with benzathine penicillin.
+Bullous impetigo → treat with dicloxacillin, 50 mg/kg every 6 hours for 10 days.
+Herpes zoster → treat with oral acyclovir and initiate immunodeficiency workup.
+Nummular eczema → treat with warm compresses and a more potent topical steroid lotion, such as fluocinolone acetonide cream.
Acne does not occur in prepubescents, and tetracycline is contraindicated in children younger than 8 years. The two types of impetigo require different treatment. Impetigo contagiosa is caused by group A, beta-hemolytic Streptococcus and progresses from a small red papule to larger, honey-colored crusted lesions. Treatment should be the same as for a streptococcal infection of the throat, since some strains are nephrotoxic. Bullous impetigo is caused by phage group II staphylococci and the lesions appear as 0.5–3 cm pustular bullae without erythema. Presumptive treatment with oral antibiotics based on the clinical diagnosis is usually sufficient. Wound cleansing and topical antibiotics are also indicated in both types of impetigo. Eczema may become secondarily infected (“impetiginized”), and may be distinguished by the distribution of lesions and clinical history. Herpes zoster (shingles) is a vesicular eruption following a dermatomal pattern and does not cross the midline.