A 5-year-old boy presented with three months of deeply
erythematous papules in a serpiginous arrangement on his lateral
abdomen. The lesions were painless and non-pruritic.
His parents could recall nothing being applied to the skin in
that area prior to the eruption, and no treatments had been
attempted. He was otherwise healthy and had no other close contacts
with similar skin findings.
What is the most likely diagnosis?