What lurks below

Sometimes the answer to a puzzling presentation comes a little closer to home

Sally is a three-year-old girl who presents with a one-day history of a red, hot, tender area on her nose, surrounding what looks like a scratch or a bite.

She is otherwise healthy, the only medical history being egg allergy. Sally is diagnosed with cellulitis and treated with cephalexin. 

The next day, she presents  with further lesions on her forehead and right upper arm. These lesions are red, hot and tender and 1cm and 4cm in diameter respectively. She is afebrile and systemically well.

She is referred to the local dermatologist who feels that the diagnosis is unclear, but that the differential should include a drug reaction and atypical erythema multiforme (most commonly caused by Herpes simplex virus).

Swabs for microscopy, culture and sensitivity, as well as HSV PCR are taken, the cephalexin stopped, and a wait-and-see approach decided upon.

Two days later, Sally’s nose and